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An Introduction for the SoutheastW W W . C R A W L S P A C E S . O R G

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CLOSED CRAWL SPACESAn Introduction to Design, Construction and Performance

by Advanced Energy

Advanced Energy, 909 Capability Drive, Suite 2100, Raleigh, NC 27606, Phone: 1-919-857-9000, Fax: 1-919-832-2696, www.advancedenergy.org

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H I G H - P E R F O R M A N C E H O M E S

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ACKNOWLEDGMENTSThis document is the result of many hours ofcollaboration with and guidance from the individualsand organizations listed below. It has been createdfrom or improved by their thoughtful contributions.However, their review or contribution does notconstitute or imply an endorsement of the contentsof this document.

Greg Baumann, National Pest ManagementAssociation

Brian Coble, Advanced Energy

Francis Conlin, mSolve

Skye Dunning, Building Performance Specialists

Steve Elder, Elder Enterprises, Inc.

Carl Falco, NC Department of Agriculture

Buddy Holliday, Hazard Mitigation Contractors, Inc.

Ed Gerhardt, Sure-Lock Homes

Arnie Katz, Advanced Energy

Marshall Knight, Marshall Knight Builder

Steve McLeod, Indoor Environmental Systems

Dan Preisach, Myers-Preisach, Inc.

James Earl Rich, Rich’s Heating & Air

William Rose, University of Illinois Urbana-Champaign

Isaac Savage, Home Energy Partners

Tim Sellers, Healthy Home Environment

Colby Swanson, Advanced Energy

Billy Tesh, Pest Management, Inc.

Dan Tingen, Tingen Construction

Jeff Tooley, The Healthy Building Company

John Tooley, Advanced Energy

AUTHORSProject Manager Cyrus Dastur,

Advanced Energy

Project Director Bruce Davis, Advanced Energy

Project Consultant Bill Warren, Bill Warren Energy Services

Advanced Energy is a Raleigh, N.C., based, privatenon-profit corporation that serves as a state andnational resource to help utility, industrial andresidential customers improve the return on theirenergy investment. Its mission is to create economicand environmental benefits through innovativeapproaches to energy. Advanced Energy wasestablished in 1980 by the N.C. UtilitiesCommission.

COPYRIGHT© 2005 Advanced Energy

This document was written with support of the U.S.Department of Energy under Contract No. DE-FC26-00NT40995. The Government reserves for itself andothers acting on its behalf a royalty-free,nonexclusive, irrevocable, worldwide license forGovernmental purposes to publish, distribute,translate, duplicate, exhibit and present thiscopyrighted document.

DISCLAIMERNeither Advanced Energy nor any person acting onits behalf: (1) makes any warranty or representation,express or implied, with respect to the accuracy,completeness or usefulness of the information inthis document, or that the use of any information,apparatus, method or process disclosed in thisreport may not infringe privately upon rights; or (2)assumes any liability with respect to the use of, orfor damages resulting from the use of, anyinformation, apparatus, method or processdisclosed in this document.

This document was prepared as an account of worksponsored by the U.S. Department of Energy (DOE)under Contract No. DE-FC26-00NT40995. However,any opinions, findings, conclusions, orrecommendations expressed herein are those of theauthor(s) and do not necessarily reflect the views ofthe DOE.

This document was prepared as an account of worksponsored by an agency of the United StatesGovernment. Neither the United States Governmentnor any agency thereof, nor any of their employees,makes any warranty, express or implied, or assumesany legal liability or responsibility for the accuracy,completeness, or usefulness of any information,apparatus, product, or process disclosed, orrepresents that its use would not infringe privatelyowned rights. References herein to any specificcommercial product, process, or service by tradename, trademark, manufacturer, or otherwise doesnot necessarily constitute or imply its endorsement,recommendation, or favoring by the United StatesGovernment or any agency thereof. The views andopinions of the authors expressed herein do notnecessarily state or reflect those of the United StatesGovernment or any agency thereof.


T A B L E O F C O N T E N T S iii

Table of Contents

Introduction . . . . . . . . . . . . .1Background . . . . . . . . . . . . . . . . . . . .2Audience . . . . . . . . . . . . . . . . . . . . . .2Using this Guide . . . . . . . . . . . . . . . .3The Ventilation Myth . . . . . . . . . . . . . .4

Section 1 . . . . . . . . . . . . . . .7Recommended Design Components

Overview . . . . . . . . . . . . . . . . . . . . . .7Moisture Management . . . . . . . . . . . .7

Blocking Sources . . . . . . . . . . . . . .8Facilitating Removal . . . . . . . . . . .12

Pest Control . . . . . . . . . . . . . . . . . . .13Combustion Safety . . . . . . . . . . . . . .15Thermal Insulation . . . . . . . . . . . . . .16Fire Safety . . . . . . . . . . . . . . . . . . . .16Radon Safety . . . . . . . . . . . . . . . . . .17Summary . . . . . . . . . . . . . . . . . . . .17

Section 2 . . . . . . . . . . . . . . .19Implementing a Closed Crawl Space

Overview . . . . . . . . . . . . . . . . . . . . .19Defining the Design . . . . . . . . . . . . .19Working With Code Officials . . . . . . .20Overcoming Conventional Wisdom . . .20Managing Labor . . . . . . . . . . . . . . . .20Managing Job-Site Logistics . . . . . . .20Providing Quality Assurance . . . . . . .22Establishing a Contract and Pricing . . .23Summary . . . . . . . . . . . . . . . . . . . .23

Section 3 . . . . . . . . . . . . . .25Sample Designs and ConstructionProcessSample designs for closed crawl spaces areprovided as architectural section drawings withdetails called out. These drawings may becopied and used as components of permitapplications or project specifications,depending on local requirements.

Overview . . . . . . . . . . . . . . . . . . . . .25Recommended Humidity

Control Methods . . . . . . . . . . . . . . .25Sample Design: Supply Air and

Floor Insulation . . . . . . . . . . . . . . .28Sample Design: Supply Air and

Wall Insulation . . . . . . . . . . . . . . . .30Sample Design: Dehumidifier and

Floor Insulation . . . . . . . . . . . . . . .32Sample Design: Dehumidifier and

Wall Insulation . . . . . . . . . . . . . . . .34Sample Closed Crawl Space

Construction Sequence . . . . . . . . . .36

Section 4 . . . . . . . . . . . . . . .39Building CodesA brief history of crawl space regulation, recentrevisions to the North Carolina residentialcode, and recommendations related to the newcode language.

Historic Origins . . . . . . . . . . . . . . . .39Revising the North Carolina

Residential Code . . . . . . . . . . . . . .39Requirements of the New North

Carolina Residential Code . . . . . . . .40Other North Carolina Residential

Code Issues . . . . . . . . . . . . . . . . . .42

Section 5 . . . . . . . . . . . . . . .45Improving Wall-vented Crawl SpacesTopics related to improving a wall-vented crawlspace and converting a wall-vented crawlspace to a closed crawl space. Retrofitting anexisting crawl space presents a variety ofcomplications that are not usually present innew construction.

Overview . . . . . . . . . . . . . . . . . . . . .45Steps for Improving a Wall-vented

Crawl Space . . . . . . . . . . . . . . . . . .45Basic Maintenance for Crawl Spaces. . 48

Section 6 . . . . . . . . . . . . . . .49 Research ResultsPresents results from Advanced Energyresearch, including detailed results comparingthe performance of closed crawl spaces to wall-vented crawl spaces in a multi-year controlledexperiment in eastern North Carolina.

Overview . . . . . . . . . . . . . . . . . . . . .49Quantifying Existing Crawl Spaces . . .49Field Study Experimental Setup . . . . .50Instrumentation and Data Collection . .51Moisture Performance . . . . . . . . . . . .52Temperature Conditions . . . . . . . . . .54Energy Performance . . . . . . . . . . . . .54Radon Measurements . . . . . . . . . . . .56Mold Sampling Results . . . . . . . . . . .56Research Implications . . . . . . . . . . .57

Continued on next page

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Section 7 . . . . . . . . . . . . . . .59Common Questions About MoldPresents basic answers to common questions aboutmold. This guide does not provide thorough orcomplete guidance with regard to the identificationand cleanup of mold, but offers some basicinformation and several references.

What Is Mold? . . . . . . . . . . . . . . . . .59Should I Test for Mold? . . . . . . . . . . .60Should I Clean Up Existing Mold . . . .60

in My Crawl Space?Does Mold Make People Sick? . . . . . .62

Section 8 . . . . . . . . . . . . . . .63 Resources and ReferencesLists sources of supply for materials and monitoringequipment used in Advanced Energy’s closed crawlspace projects as well as references to serviceproviders and more detailed sources of information.

Products and Services . . . . . . . . . . . .63Online Resources . . . . . . . . . . . . . . .63Technical References . . . . . . . . . . . .64Other Resources . . . . . . . . . . . . . . . .64

Appendices . . . . . . . . . . . . .65 A. Quick Overview of Duct Sealing . . .65B. Simplified Psychrometic Chart . . . .66C. Wood Moisture Content at

Different Temperatures and Relative Humidities . . . . . . . . . . .67

D. Glossary of Acronyms and Abbreviations . . . . . . . . . . . .68

Index . . . . . . . . . . . . . . . . .69


I N T R O D U C T I O N 1

INTRODUCTIONThis guide is an introduction to the designcomponents, field implementation, coderequirements, and measured performance ofcrawl space construction in central and easternNorth Carolina. While a short section describessteps that builders or property owners can taketo improve traditional wall-vented crawlspaces, the majority of this guide focuses on anew design: closed crawl spaces that are notventilated with outside air.

Many of the guidelines and much of thebackground information presented in thisguide comes from the results of an ongoingAdvanced Energy research project, started inthe eastern North Carolina town of Princevillein 2001. The Princeville research projectcompares the performance of wall-vented andclosed crawl space foundations in a controlledstudy. Additional recommendations come fromother Advanced Energy research projects,including investigations of crawl spacefailures, and from collaboration with closedcrawl space installers across North Carolina.

The Princeville research project has shown thatclosed crawl spaces do a much better job ofcontrolling crawl space moisture levels than dowell-built wall-vented crawl spaces. Whilerelative humidity in the wall-vented crawlspaces exceeds 80% for the majority of thespring and summer months, the Princevilleclosed crawl space designs control relative

humidity below 65% during the same period.The research also shows that the homes builton closed crawl spaces save up to 15% onannual energy usage for heating and coolingwhen compared to the homes built on wall-vented crawl space foundations.

The Princeville project findings supported a2004 revision of the North Carolina residentialcode that governs crawl space construction.The new code language is currently availablefor use and will be enforced with the next print

release of the North Carolina code in 2006.Design guidelines that are based on therequirements of this new code language arehighlighted in the guide.

Visit www.crawlspaces.org for completeresearch reports, short videos on key concepts,article links, or to obtain an electronic copy ofthis document. When online versions of codelanguage related to closed crawl spaces areavailable, they will also be linked.

Why is the new design called a“closed” crawl space?

This guide uses the term “closed” to describe thealternative to a wall-vented crawl space design, butseveral other terms are commonly used. The term“closed” is used in the North Carolina building code.Here is a brief background on why “closed” waschosen over other options:

“Unvented”In fact, several closed crawl space designs arevented, just not with outside air. Two commontechniques are ventilation with conditioned air from aduct system and ventilation with conditioned air fromthe living space.

“Sealed”The North Carolina residential code does not define aclosed crawl space as requiring a sealed vaporretarder, which Advanced Energy recommends.Installers can differentiate this improved design fromother closed crawl space designs by calling it “closedwith a sealed liner.” Furthermore, it is impractical toperfectly air-seal a crawl space. The term “sealedcrawl space” suggests an extreme level of air sealing

and implies that any small, unsealed air leakage pathprovides grounds for failing an inspection. InAdvanced Energy’s experience, it is inappropriate torequire code officials to use such a stringent, yetvague, standard for enforcement.

“Conditioned”Not all closed crawl spaces are conditioned. A closedcrawl space that is truly conditioned must haveinsulation located at the perimeter wall and a thermalbarrier covering any foam plastic insulation. Unlessspecifically designed to do so, closed crawl spacesgenerally will not maintain the minimum 68° F (20°C) winter temperature required to qualify as a“conditioned area” as defined in the North Carolina(and International) residential code.

The words “closed,” “sealed,” “unvented” or“conditioned” will likely continue to be usedinterchangeably to refer to a variety of crawl spacedesigns that do not have ventilation with outside air.Designers, installers, and code officials will need to makesure that the chosen specifications and requirements areclearly understood, whichever name is used.

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I N T R O D U C T I O N2

Background

Crawl space foundations are widely used inbuilding construction throughout the UnitedStates, with approximately 250,000 new homesbuilt on crawl spaces every year and anestimated 26 million such homes already inexistence. They are especially common in thesoutheast, where they are found in over 9million existing homes and around 70,000 newhomes per year.

Crawl spaces are inexpensive to build,functional in terms of providing a levelfoundation for flooring on sloping sites, andconvenient spaces in which to locateplumbing, electrical lines, and ductwork forheating and air conditioning systems.Unfortunately, traditional wall-vented crawlspaces can also host a variety of seriousmoisture and insulation problems.

It is an all too common experience in thebuilding professions to enter a wall-ventedcrawl space in the spring or summer and findbeads of moisture in floor insulation, highwood moisture content, visible mold growingon surfaces, condensation on truss plates,plumbing pipes, air conditioning equipment orducts, and in some cases, rot in the woodframing. Homeowners complain of highhumidity, musty odors, buckled hardwoodfloors, and mold damage in the home above.Builders, mechanical contractors andinsulation contractors routinely bear the bruntof these complaints.

Since the 1940s, residential building codesand conventional wisdom have prescribedpassive ventilation with outside air as themeans for providing crawl space moisturecontrol. However, in the humid southeasternU.S., this prescription typically contributes tothe moisture problems listed above instead ofpreventing them.

The expense of moisture repairs and theincrease in complaints and legal action relatedto mold growth in homes have madehomeowners, property managers, tenants, andthe construction industry much more aware ofthe need to control moisture in homes. Thisawareness is helping to drive demand from agrowing number of consumers and builders toinvest the additional effort to incorporateclosed crawl space systems in both new andexisting homes. The moisture control providedby a properly closed crawl space candramatically reduce the risk and associatedliability of mold and moisture damage in thesoutheastern climate.

As a performance goal, crawl spacefoundations should certainly be free of rot.Ideally they should also minimize theconditions that lead to condensation and moldgrowth. While well built wall-vented crawlspaces may be able to control rot in thesoutheast, they cannot maintain relativehumidity below the 70% threshold thatsupports mold growth and they routinelyexperience condensation on a variety ofsurfaces in the crawl space. Closed crawlspaces can maintain relative humidity below

the 70% target and dramatically reduce thepotential for condensation on surfaces in thecrawl space.

The key components of a closed crawl spacesystem work in tandem to control the variety ofwater sources that affect crawl spaces:

• Exterior water management preventsintrusion of liquid water

• Air sealed walls minimize the entry of humidoutside air

• Vapor retarders minimize the evaporation ofwater from the ground or perimeter wall

• Mechanical drying systems provideongoing, active removal of water vapor

• Drains or pumps remove water coming fromplumbing leaks or floods

Audience

This guide is intended to provide usefulinformation to a broad range of stakeholders inthe residential construction industry.

For builders and closed crawl space installers,we hope this reference provides effectiveguidance towards good design andimplementation of closed crawl spaces, withtips about pitfalls to avoid and availablealternatives. The background information oncode development and field research is offeredto help you gain acceptance of your closedcrawl space designs by code officials and sub-contractors.



For code officials, we hope that the discussionon the development and components of theNorth Carolina residential code provides aresource for understanding the newly availablecode language. Outside of North Carolina, weoffer this information as a resource for thedevelopment and adoption of similar codelanguage to meet the needs of other regions.

For property owners and private homeinspectors, we hope that this guide providesknowledge for assessing existing wall-ventedor closed crawl spaces as well as tools forspecifying and purchasing new closed crawl spaces.

Using this Guide

The closed crawl space designs and processespresented in this guide are not the only onesthat are acceptable. They are simply examplesthat have performed successfully in AdvancedEnergy field testing or in projects byprofessional installers in North Carolina. Thereare many other closed crawl space designs thatcan perform acceptably and that meet therequirements of the North Carolina residentialbuilding code. As we verify the performance ofadditional designs and techniques we hope toadd them to this reference, along with updatedinformation gained from long-term monitoring.

It is important to keep in mind that the designsand techniques presented in this guide are notdefinitive specifications. If you are a builder,

property owner, or other contractor planning toinstall closed crawl spaces, we invite you toadjust these designs and processes to yourlocal site conditions, code requirements, homedesign, construction processes and occupantneeds to ensure success. Remember thatclosed crawl spaces share the samevulnerability of other foundation types orresidential water control components: Just likebasements, slabs, window and roof flashings,foundation waterproofing or plumbing, aclosed crawl space that is installed improperlycan do more harm than good.

Please note that the sample designs andprocesses discussed here have been tested

primarily in low-volume construction of closedcrawl spaces in small homes with simplefoundation plans. Builders of the morecomplex homes typically found in mainstreamresidential construction will likely need toadjust the sample construction process,especially if they build in high volume. FutureAdvanced Energy research will focusspecifically on the delivery of closed crawlspaces in the production builder environment.

We anticipate that the performanceimprovements seen in closed crawl spaces inthe Princeville project will translate very well tosimilar homes throughout the southeasternU.S. Future Advanced Energy research will also

A view of the homes in the Princeville research project. Six homes are located on each side ofthe same street.

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I N T R O D U C T I O N4

confirm whether closed crawl spaces deliversimilar improvements for moisture control andenergy use in homes of different geometry indifferent climates.

The Ventilation Myth

Why doesn’t ventilation with outside summerair dry out a southeastern crawl space? Thetraditional method of controlling moisture incrawl spaces is to provide passive ventilationwith outside air. However, wall-vented crawlspaces routinely experience moisture problemslike condensation, surface mold growth, highwood moisture content, or wood rot. Thetypical “cure” for such problems has been toadd more ventilation, either in the form ofadditional ventilation openings to the outsideor by installing a fan or multiple fans tointentionally move more outside air throughthe crawl space. Advanced Energy research hasconfirmed over the long term what we andother building scientists have measuredrepeatedly in previous short-terminvestigations of crawl space failure: theoutside air contains more water vapor than theair in the crawl space during the warmseasons, and has no potential to dry the crawlspace. Instead, the outside air ends upcontributing water vapor to the crawl space.

To understand why, first we need to definethree properties of air: temperature, relativehumidity, and dew point temperature.Temperature is the most familiar property, and

is simply a measure of the heat in the air. Butwhat exactly is relative humidity?

At any moment, the air around you contains acertain amount of water vapor. At the currenttemperature, there is also a limit to how muchwater vapor that air can contain before thewater vapor condenses into liquid water…better known to us as “condensation” or “rain”.Relative humidity is the ratio of actual watervapor in the air to the maximum amount ofwater vapor that the air can possibly hold atthe current temperature. So, the relativehumidity changes if either the amount of watervapor in the air changes or the temperature ofthe air changes. If the relative humidity in onelocation is 90% and the relative humidity inanother location is 40%, you can’t tell whichlocation has more water vapor unless you alsoknow the air temperatures. Cold air can holdless water vapor than warm air, so if air getscooler without losing water vapor, its relative humidity increases.

Dew point temperature, often just called “dewpoint,” is a more direct indication of how muchwater vapor is in the air. If you change thetemperature of air without adding or removingwater vapor, the dew point stays the same. Ifyou remove water vapor, the dew point goesdown whether or not the air temperaturechanges. If you add water vapor, the dew pointgoes up whether or not the air temperaturechanges. As you might guess, the dew pointmeasurement tells you the temperature atwhich the water vapor in the air will condenseinto liquid water, either because the air cools

down to the dew point temperature, or becausethe air comes into contact with a surface that iscooler than its dew point temperature.

Psychrometric charts and slide rules allow youto calculate the unknown third property of air ifyou know the other two, for example, calculatingdew point when the air temperature and relativehumidity are known. They can calculate thechange in one property if another property ischanged. You can generally obtain apsychrometric chart or slide rule frommanufacturers of air conditioning ordehumidification equipment, and there areseveral on-line psychrometric calculators on theInternet. We have provided a simplified versionof the ACCA (Air Conditioning Contractors ofAmerica) psychrometric chart in Appendix B.

As an example, let’s look at the properties of airon a mild summer day in North Carolina. Let’ssay it’s 85° F (29° C) outside and the relativehumidity is 60%. Conventional wisdom tells usthat this air is warm and dry, so it should be greatfor ventilating a crawl space. Using a slide rule orchart, we determine that the dew point of this airis 70° F (21° C), which is relatively drycompared to typical conditions. Now let’s assumethat air goes into the crawl space. A typicalsummertime temperature in a wall-vented crawlspace is 73° F (23° C), so the outside air coolsdown. No water vapor has been removed, so thedew point stays at 70° F. The temperature hasdropped, so we need to use the psychrometricchart to find the new relative humidity… and nowit’s a whopping 90%! Furthermore, thetemperature of the ductwork, plumbing, andbottom side of the insulation are below 70° F, so



the water vapor will condense on those surfaces.It may even condense on the crawl space floor oron the wood framing! It turns out that ventilatingwith the outside air adds moisture to the crawlspace, it does not dry it out.

Summer moisture conditions in central andeastern North Carolina are often much wetter thanthe example. In the record-setting droughtsummer of 2002, the outside air dew pointexceeded 70° F 44% of the time at AdvancedEnergy’s Princeville research site. In the record-setting rainfall year of 2003, the outside air dewpoint exceeded 70° F 72% of the summer andwas higher than the temperature inside the crawlspace almost 20% of the summer.

Outside Air Dew Point and Vented Crawlspace Temperature

72

74

76

78

Aug 8 '03 12 AM Aug 8 '03 12 PM Aug 9 '03 12 AM Aug 9 '03 12 PM Aug 10 '03 12 AM

22

23

24

25

Outside Dew Point Vented Crawlspace Temperature

Tem

pera

ture

(°F)

Tem

pera

ture

(°C)

This data from the Princeville site shows thatfor most of a very humid 48-hour period, theoutside dew point exceeds 74° F (24° C) and ishigher than the temperature inside the crawlspace. If this outside air enters the crawlspace, the water vapor will condense onsurfaces inside. Note that this was not aperiod of very rainy weather; records indicateonly 0.2 inches of rainfall over this entire 48-hour period.

After noticing light mold growth on floorjoists in a wall-vented crawl space, acontractor recommended installation of apowered crawl space ventilation fan to “dry”the crawl space.

After installation of a powered crawl spaceventilation fan, so much water condensedon the floor joists that rot set in anddestroyed the lower portion of the joists.

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R E C O M M E N D E D D E S I G N C O M P O N E N T S 7

Section 1

RECOMMENDEDDESIGNCOMPONENTSOverview

This section presents a variety of designcomponents that meet or exceed the minimumrequirements for closed crawl spaces, asspecified by the North Carolina residentialcode discussed in Section 4.

The recommended design componentspresented here are not the only ones that areacceptable. They are simply examples thatperformed successfully in the field testingdetailed in Section 6, in other AdvancedEnergy research projects or by professionalinstallers in a variety of locations in NorthCarolina. There are many other closed crawlspace designs that can perform acceptably andthat meet the requirements of the NorthCarolina residential building code.

The design components presented here are notdefinitive specifications. If you are a builder,property owner, or other contractor planning toinstall closed crawl spaces, you will need toadjust these design components to your localsite conditions, code requirements, homedesign, construction processes and occupantneeds to ensure success.

The dozens of individual components thatmake up a complete and effective closed crawlspace system fall into six general categories offunction:

• Moisture management

• Pest control

• Combustion safety

• Thermal insulation

• Fire safety

• Radon safety

This section discusses each category withbackground information and then specificcomponents. The list of categories follows theorder of requirements in the North Carolinaresidential code. Several specific items, likefoundation drainage or foam plastic fire safety,are not in the crawl space code section but areincluded here in the interest of completeness.

This section uses three symbols to indicatedifferent levels of components:

A red check mark indicates a componentthat is required by the North Carolinaresidential code

A green plus sign indicates a componentthat is recommended by Advanced Energy

A gold star indicates an optionalcomponent that will provide an extra levelof performance or safety

Moisture Management

Moisture management of the finished crawlspace is the primary goal of any closed crawlspace system, and it involves components bothoutside and inside the crawl space. Moisturemanagement, for both liquid water and watervapor, uses two basic strategies:

1. Blocking sources2. Facilitating removal

Note that moisture management during theconstruction process involves severaladditional measures which are described in thesample construction sequence in Section 3.We have chosen not to present the componentsof moisture management in the order used bythe North Carolina residential code. Instead, wepresent them in order of components locatedoutside the crawl space to components locatedinside the crawl space, since this follows themodel of first blocking sources and thenfacilitating removal.✔

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R E C O M M E N D E D D E S I G N C O M P O N E N T S8

Moisture Management:Blocking Sources

Roof runoffUse a system to direct roof runoff awayfrom the house and prevent the runofffrom entering the crawl space. This isoften a gutter system, but could also be asystem of foundation waterproofing,perimeter gravel bed and a drain. Anotheroption is foundation “flashing,” forexample, a layer of impermeable materiallike EPDM rubber that extends down andaway from the foundation wall belowgrade for approximately 6 feet.

If sub-surface drain pipes or gutterleaders are used to manage roof runoff,they must not be connected to the crawlspace drain. This eliminates the chancethat blockages or heavy rains will causeroof runoff to enter the crawl space.

Exterior ground and surface water

Provide site grading around the perimeter

of the house with a minimum of 6 inches(152 mm) of fall over 10 feet (3048 mm) ofrun to direct ground surface water awayfrom the house. Swales or drains may beused if lot lines, slopes, walls, or otherbarriers prohibit the required grading.

Ensure that landscapers or propertyowners do not install flower beds, treemounds, mulch piles or other landscapingfeatures that prevent drainage away fromthe house. In-ground irrigation systems oryard sprinklers require special attentionbecause they can easily cause a waterproblem in an adjacent crawl space. Makesure these systems do not put water ontothe crawl space walls.

Provide a foundation drain system wheneverthe exterior grade is 12 inches (305 mm) ormore above interior crawl space grade. Keepfoundation drain systems separate fromcrawl space drain systems.

Provide foundation damp-proofing orwater-proofing when the exterior grade is

above the interior crawl space grade toprevent the flow of water through the wallby capillary action or “wicking.”

Raise the crawl space grade above the exteriorgrade to eliminate the need for a foundationdrain, damp-proofing or water-proofing.

Protect exterior crawl space access door(s)from roof runoff. For example, if there isno roof runoff system, locate the accessdoor on a gable end wall. Wheneverpossible, build the bottom of the access atleast 4 inches (102 mm) higher than theexterior grade. If raised access is notpossible, provide a dam or gravel drain toprevent water entry. Use non-corrodingaccess doors, especially in coastalcommunities, to prevent deterioration.

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The entrance to this closed crawl space is elevated well above exterior grade, reducing the likelihoodof water entry in heavy rains or minor flooding. Photo credit: Indoor Environmental Systems.



Humid Air

Seal all gaps between foundation wall andsill plate, sill plate and band joist, andband joist and subfloor. Seal penetrationsthrough the crawl space wall for waterservice, electrical service, plumbingfixtures, ductwork, etc. Use solid blockingand sealants to seal gaps between theexterior wall opening and ductwork foroutdoor packaged-unit heating andcooling equipment, if present.

Seal connections from the crawl space toareas under attached porches or decks,which are common sites of liquid waterintrusion or entry of humid outside air.

Houses in an area prone to flooding ordesignated as a Special Flood Hazard Area(SFHA) by the Federal EmergencyManagement Agency (FEMA) or theNational Flood Insurance Program (NFIP)must have FEMA/NFIP-compliant floodvents in the crawl space perimeter wall.See the “Flood Vents” sidebar for moreinformation.

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This foundation wall has an effective gasket between the sill and the masonry wall, butsmall gaps between the sill plate and the band joist or between the band joist and thesubfloor add up to large leak areas. Close these joints with gaskets or sealants as well. Photo credit: Building Performance Specialists.

When you see packaged unitequipment on the outside of thecrawl space… Photo credit: Healthy Home Environment.

… there are typically large gapsin the perimeter wall aroundand between the supply andreturn ducts. These gaps requiresolid backing materials andsealants for proper air-sealing.Remove any rubble underneaththe opening to reduce the risk ofdamage to the ground vaporretarder. Photo credit: Healthy Home Environment.

Seal all penetrations in theperimeter wall. Photo credit: Indoor Environmental Systems.

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When required, choose flood vents thatminimize stand-by air leakage.

Build hollow-block masonry foundationwalls with either a continuous top course

of solid masonry or the top course ofmasonry grouted solid to prevent passageof air from the interior of the wall into thecrawl space.

Evaporation from the ground andperimeter walls

Cover all crawl space ground with aminimum 6-mil polyethylene vaporretarder. Lap seams at least 12 inches(305 mm).

Cover the masonry perimeter walls withminimum 6-mil polyethylene vaporretarder, leaving at least 3 inches (76 mm)of exposed masonry at the top of the wall.Mechanically attach the vapor retardermaterial and seal it to the wall with ductmastic. Common strategies for mechanicalattachment include powder-driven nails,pins or masonry screws that hold thevapor retarder up behind a furring strip orwall insulation.

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Flood Vents

Flood vents are openings in a foundationwall that automatically allow the freepassage of flood water into and out of afoundation in order to equalize hydrostaticforces on the foundation walls. Whenrequired in a closed crawl space, choose aflood vent model that reduces standby airleakage as much as possible.

The Federal Emergency Management Agencyand the National Flood Insurance Programspecify the design requirements for floodvents as well as the guidelines for where theymust be implemented. The 2000 (and later)International Codes meet these requirements.

To determine if a property is located in aSpecial Flood Hazard Area (SFHA) and willbe required to have flood vents installed,contact your local building inspectionsdepartment or governing authority. Aproperty survey and elevation certificate maybe required before a final determination can be made.

Non-compliance with flood vent requirementscan jeopardize a community’s ability to

participate in the NFIP or to receive a widerange of federal funds for emergencyassistance, construction, property loans, andmore. For the individual homeowner,insurance premiums may go up significantlywhen insurance policies are renewed or whena house is sold if the house does not complywith flood vent requirements.

For additional information, refer to TechnicalBulletin 1-93, Openings in Foundation Walls,available from FEMA (www.fema.gov, or 800-480-2520) or contact your state’sdivision of emergency management orfloodplain management.

This flood vent has a weather strip toreduce stand-by air infiltration and thecentral panel is insulated with foam. Photo credit: Hazard Mitigation Contractors, Inc.

Do not leave any exposed earth in thecrawl space! Photo credit: Bill Warren.



Seal the ground vapor retarder to interiorcolumns at least 4 inches (102 mm) abovethe crawl space floor.

Install the ground and wall vapor retardersas a sealed liner by sealing all seams andconnections to masonry with fiberglassmesh tape embedded in duct mastic. If youchoose to use a tape product to sealseams, ensure that all surfaces are cleanbefore applying the tape and do not subjecttape joints to mechanical stress. Both ofthese situations have caused tape joints tofail in Advanced Energy research houses.

If you use unreinforced 6-mil polyethylene(the material most commonly available athome improvement retail stores), protect itwith an additional layer of durable material(for example, artificial turf, vinyl runners,or other carpet material) in storage areasor traffic areas, like a service path tomechanical equipment. Consider usingthicker, reinforced vapor retarder materialsfor improved durability and punctureresistance, and to eliminate the need foradditional protective coverings.

The ground vapor retarder must besecured to resist movement or tears.

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One way to mechanically attach a wallvapor retarder: secure it behind apreservative-treated plywood furring stripattached to the masonry with nails driventhrough washers. Photo credit: Bill Warren.

This heavy-duty vapor retarder material ismechanically supported by metal pins withcap washers and sealed to the masonrywith fiberglass mesh tape and duct mastic.Photo credit: Indoor Environmental Systems.

Vapor retarder material is attached with afurring strip three inches (76 mm) below thetop of the masonry wall and sealed to the wallwith mastic. The wall vapor retarder material issealed to the ground vapor retarder to form acontinuous liner. Penetrations, like the dryervent in the photo, are completely air sealed.The top of the masonry wall and the front edgeof the sill plate have been painted white withmastic to improve inspectability by pestmanagement professionals.

Overlap seams in the vapor retarder material to reduce thechance that liquid water running downhill from the wall or groundwill collect against the underside of the sealed seams. Lap theground vapor retarder on top of the wall vapor retarder (A) andlap downhill sections of vapor retarder over uphill sections ofvapor retarder (B).

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Secure the ground vapor retarder materialas necessary to resist movement due toanticipated traffic. Anchor 6-milpolyethylene with sod staples or

galvanized spikes through washers ornailing tins on approximately 12 foot(3658 mm) centers. Use additional staplesor spikes to secure the vapor retarder insteeply sloped areas or in heavy trafficareas like the crawl space entrance orservice paths. Heavier vapor retardermaterials in small crawl spaces or in largecrawl spaces with intermediate piers maynot need any staples or spikes.

Moisture Management:Facilitating Removal

Please remember that moisture still gets into aproperly closed crawl space. Ground moisturecan wick up through masonry walls or supportcolumns and evaporate into the crawl space.Rain can wick through the perimeter masonrywall or sill plate and evaporate into the crawlspace. Wind, duct leakage or other buildingpressures will inevitably force some amount ofhumid air through the perimeter wall, since it’simpossible to do a perfect air-sealing job.Plumbing failures or floods put liquid water inthe crawl space.

For all these reasons, a closed crawl spaceneeds components that remove both liquidwater and water vapor. Duct leakage anddiffusion of water vapor to the house abovemay provide some drying potential for a closedcrawl space, but an intentional dryingmechanism is required to ensure adequatemoisture management.

Some installers and researchers have theorizedthat the moisture control improvements ofclosed crawl spaces allow the mechanicalcontractor to down-size the installed heatingand cooling equipment. However, there are fewcommonly available tools at the time of thiswriting to calculate the impact of a closedcrawl space on the sizing of mechanicalequipment for the home.

Grade the floor of the crawl space to one ormore low points. Provide a drain or sumppump at each low point to remove liquidwater from the crawl space in case of aplumbing leak or other flooding event.

Use a backflow valve in crawl space drainsand a check valve in sump pump out-flowpipes to prevent reverse flow of outsidewater into the crawl space and to reducethe chance of vermin entry. Floor drainswith p-traps that connect to the whole-house plumbing waste drain or to amunicipal sewer system may allow entryof sewer gases if (when) the trap dries outand pose a risk of sewage backup.

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Why does Advanced Energyrecommend installing the vaporretarder as a sealed liner?

Advanced Energy recommends the use of asealed vapor retarder covering the walls andground because we have field tested thisdesign as part of a system that providedeffective crawl space moisture management.Sealing the seams of the vapor retardermaterial reduces the risk of damage whenpeople move around in the crawl space, andmakes it more likely that a water failure like aplumbing leak will be discovered. The sealedliner is not designed to prevent intrusion ofliquid water from the ground, but it will makeit less likely. Another unintended benefit maybe improved resistance to the movement ofsoil gases into the crawl space.

Choosing to not use a vapor retarder on theperimeter walls will typically result in moremoisture entering the crawl space duringwarm weather. Choosing not to seal theseams of the ground vapor retarderincreases the chance that ground will beexposed. Such a system can still performacceptably if the installed drying mechanismis capable of removing the resultingadditional moisture load.

This crawl space drain and backflow valveassembly is ready for installation. Photo credit: Indoor Environmental Systems.



Terminate crawl space drains or sumppump discharges in ways that reduce therisk of damage or blockage. For example,surround the termination with gravel orshrubbery to reduce the risk of soilblockage or damage from lawn equipment.

Provide a mechanical drying system toremove water vapor. Six methods areallowed under the NC residential codediscussed in Section 4. See the next itemfor recommended strategies.

Use conditioned air from the supply-sideductwork or stand-alone dehumidifiers tomeet the requirement for a mechanicaldrying system. Advanced Energy has fieldtested both of these methods. See Section3, Sample Designs and ConstructionProcess, for a detailed description of thesetwo drying mechanisms and discussion ofadvantages and disadvantages for each.

Terminate appliance water discharge pipes(for example, water heatertemperature/pressure relief valves, airconditioner or dehumidifier condensatedrains, or water softener discharges) tooutside, to an interior pump, or to a crawlspace drain.

Drain appliance discharge pipes directly tooutside or to an interior pump, not tocrawl space drains. If the backflow valve inthe crawl space drain is installed out oflevel or if there is water in the drain pipeexerting pressure on the backflow valve,appliance discharges may build up

significantly inside the crawl space beforethey can drain out.

Include relative humidity monitors orliquid water detectors in the design toinform occupants of the performance ofthe system.

Install auxiliary condensate drain panswith float kill-switches under air handlersor dehumidifiers in a closed crawl spacefor added security against overflows dueto blockage in the condensate line.

Terminate clothes dryer exhaust vents to outside.

Terminate all kitchen and bathroomexhaust vents to outside.

Pest Control

Two important goals of a closed crawl spacedesign are to

1. Avoid increasing the risk of damage fromsubterranean termites or other insect pests

2. Provide the ability for pest managementprofessionals to inspect the structure andprovide treatment, when necessary.

Under North Carolina structural pest controlregulations, pest management professionalsare not liable for infestations or damagealready present in hidden or obstructed areas

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The finished ground vapor retarder issealed directly to the drain opening. Photo credit: Indoor Environmental Systems.

Use sump pumps if desired or when gravitydrains are not feasible. This model includesa cap for the housing and an optional liquidwater alarm to detect a failure of the sumppump system. Photo credit: Indoor Environmental Systems.

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when they perform inspections for real estatetransactions if the professional identifies suchareas on the inspection report. The definitionof “hidden or obstructed” includes areas of thebuilding that would require disassembly withtools or removal of pieces or parts of thebuilding to allow for inspection.

For properties under a service contract orwarranty, the pest management contractor maybe held responsible for any and all damagethat occurs to the property after the date oftheir treatment. This discourages them fromcontracting on properties with hidden orobstructed areas. In new construction projects,pest management contractors may be reluctantto provide soil pre-treatment, wood pre-treatment, or an alternative pre-constructiontreatment unless they have sufficientinformation about the closed crawl spacedesign to believe that they will have adequateaccess for the pre-treatment or for futureinspections or treatments.

Closed crawl space designs must payparticular attention to materials applied on theperimeter walls, since this is a common pathfor wood-destroying insects from the ground tothe structure. It is not acceptable to drapeinsulation or vapor retarder materials from theband joist or sill plate to the crawl space floorbecause this prevents inspection.

Provide a termite inspection gap of atleast 3 inches between the top of any wallvapor retarder material and/or perimeterwall insulation and the top of theperimeter masonry wall. Vapor retarder orinsulation materials must not contact anywood framing.

Provide a clearance or wicking gap of atleast 3 inches between the bottom of anyperimeter wall insulation and the crawlspace floor surface.

When the perimeter wall of a closed crawlspace is insulated, the band joist mustalso be insulated.

❍ The use of rigid foam on the bandjoist will seriously impair visual orphysical inspection (“probing” or“sounding”) of the band by a pestmanagement professional, because thefoam may be damaged in the processor impossible to replace in its originalcondition. Foam insulations with low(< 1 perm) permeability to water vaporwill reduce the ability of the band todry to the crawl space, but would alsoreduce the potential for condensationon the band when the band is cold.

❍ Insulating the band joist with facedbatt insulation, with the vapor retarderfacing towards the inside of the crawlspace, facilitates inspection ortreatment by a pest managementprofessional since it is more easilyremoved and replaced withoutdamage. This strategy allows somedrying of the band joist to the crawlspace during the cooling season, butmay increase the chance ofcondensation on the band when theband is cold. The facing material mayneed to be fire-rated for direct exposure.

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This crawl space under construction hascareful detailing at all beam pockets tomaintain the termite inspection gap at everyinterface of masonry and wood. Photo credit: Building Performance Specialists.



Combustion Safety

Gas- or oil-fired appliances, such as furnaces,water heaters, or boilers, need combustion air.Without sufficient combustion air, theappliance can produce carbon monoxide or failto draft properly. Advanced Energy hasdocumented numerous cases in whichcombustion equipment in wall-vented crawl spaces

1. did not have sufficient combustion airvolume or openings to the outside permechanical code requirements,

2. generated unacceptably high levels ofcarbon monoxide, or

3. did not draft acceptably due to air pressurescreated by duct leakage or stack effect.

A properly air-sealed closed crawl space ismuch tighter than a wall vented crawl space andcan even be tighter than the house above. As aresult, Advanced Energy recommends that:

Atmospheric or“natural” draftappliances shouldnot be installed in aclosed crawl space.

Fuel-burning appliances located in aclosed crawl space shall obtaincombustion air from outdoors per theNorth Carolina Mechanical Code. Notethat the use of passive combustion air

openings is not acceptable because itviolates the air-sealing requirements forthe perimeter wall around and the floorabove the closed crawl space.

Specify direct-vent (“two-pipe”) models toensure adequate combustion air whenfuel-fired appliances are used. All air forcombustion should be piped directly fromoutside into the appliance and allcombustion exhaust gases should bepiped directly from the appliance tooutside. Some manufacturers haveseparate cabinets or enclosures that canbe used to convert non-direct-ventappliances to direct-vent operation.

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The two large PVC pipes entering thisdirect-vent furnace bring combustion airfrom outside and take exhaust gases tooutside to ensure that the furnace will notbackdraft or burn inefficiently in thepresence of negative building pressures.Photo credit: Bill Warren.

General Combustion Safety

Regardless of whether or not a home hasa closed crawl space foundation,combustion safety is a serious issue.Over 200 people die every year in theU.S. from carbon monoxide (CO)poisoning due to faulty combustionappliances in the home. Thousands ofpeople require emergency room treatmentfor exposure to high levels of CO, andresearchers are still working tounderstand the potentially serious effectsof chronic low-level exposure to CO.

Advanced Energy recommends theuse of carbon monoxide low-levelmonitors or alarms in any home(including homes with slab orbasement foundations) that has anattached garage or any fuel-firedcook stove, furnace, boiler, waterheater, fireplace, or other appliance.

For additional protection, considerusing a fuel-gas alarm when thereare gas-fired appliances or gas linesin a home. These alarms can detectleaks of propane or natural gas andalert occupants to the problem.

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Thermal Insulation

The North Carolina residential code allowsinsulation in a closed crawl space to be locatedat the sub-floor or at the perimeter wall. Thisconflicts with the 2004 Supplement to theInternational Residential Code, which requiresinsulation in an “unvented” crawl space to belocated at the perimeter wall only. The researchresults in Section 6 showed that closed crawlspaces with either floor or wall insulationsimilarly outperform wall-vented crawl spaceswith floor insulation in central North Carolina.

Perimeter wall insulation may be locatedon any combination of the interior surface,exterior surface or inside of the perimeterwall, or the perimeter wall itself mayprovide the required R-value.

If the perimeter wall is insulated, theninsulation must be installed on the bandjoist. See “Pest Control” above for noteson options for band joist insulation.

Perimeter walls that are partially masonryand partially wood framed (the woodframed portion is commonly referred to as a “pony wall”) do not require insulation on masonry wall heights of 9inches or less.

Use non-porous insulation (for example, aclosed-cell foam insulation) if the insideof the perimeter wall is insulated. Thisreduces the risk of contamination or other

damage to the insulation if there is a waterleak or flood.

Install insulation at the sub-floor withoutgaps or compression and in full contactwith the sub-floor to achieve the nominalR-value. Insulating open-web floor truss systems with batt insulation isdiscouraged due to the difficulty ininsulating the openings in the trussstructure. Better options for insulatingopen-web floor truss systems includeusing spray foam or netting the bottom of the trusses and completely filling thecavity with blown insulation. Thesestrategies would likely also improveinsulation performance in wooden I-beam floor structures.

Fire Safety

A key element in residential fire safety isfireblocking between different levels in a home.Fireblocking requirements already exist in theresidential building code, but allow the use ofporous materials like fiberglass or rock woolinsulation. North Carolina has improved theserequirements to require the use of non-porousmaterials for fireblocking in crawl spaces.

Foam plastic insulation receives specialscrutiny in residential building codes becausesome foam insulations have the potential torelease toxic or flammable gases when heated,or they can accelerate the spread of a fire if

they ignite. To reduce these risks, most codesrequire a thermal barrier (typically 1/2 inch [13 mm] gypsum board or equivalent) or anignition barrier (typically 3/8 inch [10 mm]gypsum board or equivalent) over foaminsulation. However, several foam insulationproducts have been designed and tested toreduce or eliminate those risks. Such productscan be installed without a thermal barrier orignition barrier with the appropriatedocumentation.

Seal all plumbing, electrical, duct,plenum, gas line and other wiringpenetrations through the subfloor with non-porous materials. Rock wool or fiberglass insulation alone is not sufficient.

Provide documentation of product fire-ratings (in the International Code CouncilNational Evaluation Report (ICC NER) forthe product) to allow installation ofexposed foam insulation without a thermalbarrier or an ignition barrier, if applicable

Provide documentation of fire-rating toallow installation of exposed facingmaterials on batt insulation in the bandjoist or pony walls, if applicable

Do not use a crawl space to storegasoline, solvents, or any tools ormaterials that present a fire hazard.

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Radon Safety

Radon is an odorless, colorless gas that is thesecond most common cause of lung cancer inthe United States, resulting in over 20,000deaths per year. An estimated 1 in 15 U.S.homes has a high level of radon. For thesereasons, the U.S. Surgeon General and theEnvironmental Protection Agency (EPA)recommend that all homes be tested for radon.

For jurisdictions where radon-resistantconstruction is required, radon controlmethods are specified in Appendix F of theInternational Residential Code. Table AF101(1)lists the counties identified by theEnvironmental Protection Agency (EPA) asHigh Radon Potential (Zone 1) counties. TheHigh Radon Potential designation indicatesareas with expected radon concentrations of 4pCi/L (picocuries per liter) or greater, where itis likely that radon-resistant construction willbe required.

The EPA recommends that all homes withradon concentrations of 4 pCi/L and greater bemitigated. The EPA also recommends that thecounty listing be supplemented with otheravailable state and local data, for example, datafrom state radon offices, public health agenciesor cooperative extension services, to furtherunderstand the radon potential of Zone 1 areas.

When radon mitigation is required, therequirements for floor sealing, duct sealing,ground vapor retarder, access door air sealing,and damp proofing of a closed crawl space

system are compatible with the requirements ofAppendix F. Sub-slab or sub-membranedepressurization systems may be utilized in aclosed crawl space in the same manner as in aslab, basement or wall-vented crawl spacefoundation. Local jurisdictions may requireadditional measures for the ground substrate,foundation wall, concrete joints, condensatedrains, or sump pits in wall-vented or closedcrawl spaces.

Summary

The dozens of individual components thatmake up a complete and effective closed crawlspace system fall into six general categories offunction:

• Moisture management

• Pest control

• Combustion safety

• Thermal insulation

• Fire safety

• Radon safety

You might be wondering “Do I really need tofollow all of the recommendations in thissection to have a closed crawl space thatworks?” The short answer is “no.” There areother designs that will perform successfully.The key for acceptable moisture managementis that the rate of moisture removal from thecrawl space must be at least as much as the

rate of moisture entry. So for example, if youchoose not to install a wall vapor retarder, thenyou need to ensure that the drying mechanismyou install is sufficient to provide the desiredmoisture management despite the extramoisture load of the exposed perimeter walls.This may require a trial and error approachsince there are no readily available tools toaccurately predict such moisture loads and sizethe drying mechanism.

Altogether, these recommendations representclosed crawl space components that haveproven their performance in real-world fieldtests. They perform as a system, and althoughit’s obvious that some components, likepreventing water intrusion, are critical, we havenot experimented to determine which of theother components could be sacrificed withoutcompromising the system as a whole.

It is important to keep in mind that thesesample design elements were tested in smallhomes with very simple foundation plans. Toensure success, builders of the more complexhomes typically found in mainstreamresidential construction will likely need toadjust the designs to accommodate local siteconditions, code requirements, home design,construction processes and occupant needs.

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18


I M P L E M E N T I N G A C L O S E D C R A W L S P A C E 19

Section 2

IMPLEMENTING ACLOSED CRAWLSPACEOverview

It would be wonderful if simply having a gooddesign guaranteed a closed crawl space thatcontrols moisture and saves energy. But in thereal world the end result also depends on thematerials, process and workmanship that putthe good design into practice.

There is no trade association or industry-accepted set of standards for implementingclosed crawl space systems beyond therequirements of the residential building code.The residential building code specifiesminimum requirements for what must be done,not necessarily the process for how it must bedone. Therefore, the implementation guidelinesAdvanced Energy recommends in this sectionare not legal requirements, but are likely to becritical to the successful implementation of aclosed crawl space.

Property owners, general contractors, or otherscan adapt the design and implementationrecommendations in this guide to their specificcircumstances to create a closed crawl spaceor they can seek a professional installer to do

the work. In some regions, owners andbuilders may have to do the work themselvesdue to a lack of local experienced installers.

Advanced Energy divides implementationguidelines into six broad topics:

• Defining the design

• Working with code officials

• Overcoming conventional wisdom

• Managing labor

• Managing job site logistics

• Quality assurance

A seventh topic applies when you hire an installer:

• Establishing a clear contract and pricing.

Defining the Design

You or your installer may prefer one closedcrawl space design to others, but should alsobe able to customize the choice of materials ordrying mechanism to suit the needs of thehouse design or local residential coderequirements. Factors like site conditions,

Finding a Quality Installer

More and more businesses are offering theservice of closing crawl spaces. Currently, youcould purchase a closed crawl space in centralNorth Carolina from:

• Home performance contractors

• Pest management contractors

• General contractors

• Professional engineers

• Mechanical (HVAC) contractors

• Insulation contractors

• Foundation repair/waterproofing contractors

Although hiring an installer to provide a closedcrawl space may be more expensive up front thandoing it yourself, the knowledge and experience

of a quality installer can be well worth theadditional expense.

Finding a quality installer typically requiresidentifying providers of closed crawl spaces inyour area and then getting proposals from severalproviders for the specific job at hand to make anapples-to-apples comparison. Ideally you wouldlook at previous work and talk with previousclients to assess the provider’s performance.Assess the knowledge, experience and integrity ofthe provider with regard to the sevenimplementation topics described in this section.The potential benefits and risks of installing aclosed crawl space demand that the work isperformed the right way at the right time.Advanced Energy recommends that you think ofthe closed crawl space installer as a partner inmoisture management, not as just another “sub”on the project.

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I M P L E M E N T I N G A C L O S E D C R A W L S P A C E20

occupant requirements, or cost will alsoinfluence the design. For example, ahomeowner with severe allergies may choose adehumidifier to dry the crawl space instead of asupply air strategy. A home on a steeply slopedsite may require such a large amount of wallinsulation that it is financially advantageous touse a floor-insulated design.

Working with CodeOfficials

You or your installer will need to work withyour local code officials to ensure that yourclosed crawl space design is acceptable andeither meets or exceeds all code requirements.Coming to agreement early and avoidingsurprises during construction are keystrategies for preventing any delay in theissuance of a certificate of occupancy at theend of construction. In some cases, local codeofficials may require or accept a stamped letterof approval from a registered professionalengineer as an alternate path for permitting and inspection.

Note that software programs for energyanalysis may not accurately predict the energysavings associated with a closed crawl space.If the home is required to meet a particularModel Energy Code or International EnergyConservation Code standard, the softwaremight require additional efficiency measures inthe house. Arguably, these measures are not

necessary and this may require negotiation toavoid installing the additional efficiency measures.

If you are hiring an installer, ask candidateshow they ensure acceptance of their work bycode officials.

OvercomingConventional Wisdom

At some point in the process, you or yourinstaller may need to overcome theconventional wisdom of constructionprofessionals who still believe that crawlspaces need ventilation with outside air, or whodo not recognize the potential risks of wall-vented crawl spaces. For example, a pestmanagement professional may refuse to treator provide a warranty on a home with a closedcrawl space. In some cases you may be able touse the information in this guide or otherresources to convince the professional of theacceptability and benefits of closed crawlspaces, but in other cases you may need toswitch to another service provider to keep theproject on schedule.

Managing Labor

You or your installer need to ensure thatemployees are trained in the use of thematerials and processes required to install a

closed crawl space system. Naturally, crawlspace work is difficult due to the confinednature of the space. It may also presentrespiratory hazards. Advanced Energy has nottested mold levels in new closed crawl spacesduring construction, but given the high levelsof airborne mold spores measured in our crawlspace research projects whenever settled dustis disturbed in finished crawl spaces,Advanced Energy recommends that workerswear respiratory protection in both new andexisting crawl spaces. We recommendcombined High-Efficiency ParticulateArrestance (HEPA) and activated carbon filtersat a minimum. Those with beards shouldconsider using full-face powered air-purifyingrespirators. Workers may need to be tested forrespirator fit and lung function according toapplicable Occupational Safety and HealthAdministration (OSHA) regulations.

Managing Job-SiteLogistics

You or your installer will need a process forcoordinating with the other building trades toensure proper scheduling and to reduce therisk of damage to the closed crawl spacesystem during construction or after the houseis turned over to a customer. Contractors youmay need to coordinate with include the:

• Site grading and preparation contractor

• Foundation or masonry contractor


I M P L E M E N T I N G A C L O S E D C R A W L S P A C E 21

• Pest management company

• Framer

• Plumber

• Electrician

• Insulator

• Mechanical contractor

• Gutter installation contractor

• Landscaping and/or irrigation contractors

• Cable TV, security system, or computernetwork wiring contractors

In particular, you or your installer mustcoordinate as soon as possible with the pestmanagement professional to ensure that theclosed crawl space system does not interferewith their treatment or affect their warranty, ifapplicable. For properties under a servicecontract or warranty, the pest managementcontractor may be held responsible for any andall damage that occurs to the property after thedate of their treatment. This discourages themfrom contracting on properties with hidden orobstructed areas. In new construction projects,pest management contractors may be reluctantto provide soil pre-treatment, wood pre-treatment, or an alternative pre-constructiontreatment unless they have sufficientinformation about the closed crawl spacedesign to believe that they will have adequateaccess for the pre-treatment or for futureinspections or treatments.

Managing moisture during the process ofconstruction is critical, because all crawlspaces, including closed crawl spaces, can

become ideal environments for growing moldas soon as the sub-flooring is installed. Moldcan grow on all surfaces in the crawl space,but it is most readily noticed when it grows onthe wood framing or subfloor. When excesshumidity drives up the wood moisture contentto 19% or more, conditions are right forsurface mold to appear. In some cases,dramatic mold blooms can grow in as little as48 hours. Seeing surface mold on the crawlspace wood in the past was seldom an issuewith homebuyers, but now public concerns

about mold can slow or prevent a home sale.Mortgage providers may even require a moldtest prior to a home purchase.

Often, the processing, transport and job-sitestorage of wood framing and subfloor materialsexposes them to rain for long periods of time.The materials may arrive on the job site alreadycontaminated with mold growth or wet enoughto foster germination of the mold spores thatthey will inevitably be exposed to. Using wetmoldy lumber defeats the purpose of anyrecommended moisture management practices.

Beware of Long Construction Schedules

Volunteer-built homes and large homes,particularly large custom homes, often have longconstruction periods before they are dried in. Thismakes it even more likely that the crawl space willbe wet before the house is dried in. Building overlong time periods requires a process that includesearly rain water management, ground cover anddehumidification to successfully avoid moldcontamination.

Another strategy could be to build such homeswith a temporary ground vapor retarder andfoundation vents and leave the vents open prior todry-in, at which time you could begin theconversion to a closed crawl space. This approachmight provide enough drying potential to avoidmold growth during the dry times of the year or indry climates, but likely won’t when constructionoccurs primarily in spring or summer.

In some cases, the only feasible strategy forimplementing a closed crawl space may be to justbuild the house with a traditional wall-ventedcrawl space, and either perform some moldcontrol or cleanup activities during construction,or to wait until the house is complete and thenconvert the wall-vented crawl space to a closedcrawl space, with any desired cleanup. . In thesecases, it may be possible to suppress moldgrowth in the floor structure prior to the crawlspace being closed by using pre-treated woodproducts or applying fungicidal coatings tountreated wood products.

If feasible, provide a waterproof covering, securedto resist wind damage, to prevent rain fromentering the crawl space when construction willstop for a prolonged period. In such cases, adehumidifier may also be needed to prevent mold growth.

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I M P L E M E N T I N G A C L O S E D C R A W L S P A C E22

Even when you install dry materials, once thesubfloor is installed the crawl space becomesan enclosed space that can trap moisture. Thesubfloor prevents excess water from dryingwith sunlight, and there is much less potentialfor liquid water or water vapor to leave thespace. The crawl space is vulnerable to majorrain or snow entry until the house is dried-inby installing the roof, wall sheathing, windows,and exterior doors.

The sample implementation process listed in Section 3 includes steps designed toprevent moisture problems during theconstruction process.

Providing QualityAssurance

Quality builders and installers care about thelong-term performance of their closed crawlspace system and will usually offer one or moreof the following quality assurance options:

• A monitoring system to inform thehomeowner of relative humidity levels in thecrawl space

• A water alarm to inform the homeowner of abuildup of liquid water in the crawl space

• A posted sign or signs identifying thedifferent components of the system andinforming anyone entering the crawl spaceof the importance of maintaining theintegrity of the system.

• A repair kit for fixing small areas of damageto the liner after the house is occupied

• An annual monitoring service to replacebatteries in monitoring systems and checkthat the crawl space system is in goodworking order. This may includemeasurements of wood moisture content orair tightness, or a download and analysis of

data logging equipment

• A guarantee or warranty that relative humiditywill be maintained below an agreed-upontarget (for example, a guarantee for relativehumidity not to exceed 70% at a specifiedmonitoring point for more than 7 consecutivedays) with exceptions for water leaks orintrusion outside the installer’s control

Basic Maintenance for Crawl Spaces

Most people don’t like to go into crawlspaces, but periodic inspection of any crawlspace helps to ensure that any problems arecaught before they cause damage. Propertyowners can perform these inspections andbasic maintenance checks themselves orhire a private home inspector or othercontractor to do it for them.

Property owners should:

• Ensure that access doors are closed,especially during warm weather.

• Ensure that drains or sump pumps arefunctioning properly

• Ensure that dehumidifiers are maintainedper the manufacturer’s instructions and arein proper working order

• Ensure that there are no solvents, gasolineor other potentially hazardous materials inthe crawl space.

• Inspect the crawl space regularly to:

❍ Identify vapor retarder damage or waterproblems. Note that small water leaksin a crawl space may not be indicatedby relative humidity sensors.

❍ Ensure that no damage occurs whenany contractors work in the crawlspace.

❍ Check and replace batteries as neededin sensors or alarms.

• Ensure that any water intrusion, especiallyflooding, is quickly drained or pumpedout of the crawl space.

One of these items doesn’t belong in acrawl space… Photo credit: Indoor Environmental Systems.


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• A guarantee or warranty against growth ofvisible mold for a specified period of time,with exceptions for water leaks or intrusionoutside the installer’s control

• References for quality assurance inspectionsby independent third parties

• Guidelines for basic maintenance of thecrawl space system (see sidebar on page 22)

Establishing a Contractand Pricing

If you choose to hire an installer to implementa closed crawl space, the installer should havea contract or plan that clearly spells out whatthey are responsible for, and what the builderor other contractors are responsible for.Responsibilities for other contractors mightinclude foundation waterproofing, foundationdrains, grading, and/or installation of thedrying mechanism if it requires a licensedelectrician or mechanical contractor and thecrawl space installer is not licensed.

Contracts may also specify financial incentivesor penalties geared towards ensuring anefficient installation. For example, there may bea trip charge assessed when the builder callsthe installer to the site but has not completedthe work necessary for the installer to proceed,or a back charge assessed if the builder orother trades damage the crawl space system tothe point that it requires repair or replacementof any component.

Currently in North Carolina, pricing fromcontractors providing closed crawl spacesystems to general contractors for newconstruction ranges from $1.00 to $3.50 persquare foot of crawl space floor area for avariety of installations. Some factors that affectpricing are the number of piers in a crawlspace, height above or below grade, height ofperimeter walls, or the complexity of thefoundation footprint. These sample installationcosts do not take into account the costreductions that the builder may realize from nothaving to install features like insulation ordrainage, since they may be included in thepricing of the closed crawl space system.

Initial costs associated with building closedcrawl spaces will generally be more than fortraditional wall vented construction. As newconstruction methods are evaluated both bybuilders and researchers, it will be important tofactor in the value of reduced callbacks due tomoisture and mold issues, the perception ofenhanced value by the consumer, and potentialfor increased sales price and reduced legalexposure. Reduced maintenance, a reduction incostly, long-term repairs, and significantenergy savings enhance the value of closedcrawl space construction to the consumer,appraisers and realtors. The future might eveninclude insurance premium reductions forhouses built on closed crawl spaces.

Summary

Successful implementation, whether by aproperty owner, builder, or professional closedcrawl space installer, must address six maintopics:

• Defining the design of the closed crawl space

• Working with code officials to ensureacceptance of the design

• Overcoming the conventional wisdom thatfavors venting with outside air

• Managing labor, including training and safety

• Managing job site logistics, especiallymoisture management and coordination withother trades

• Providing quality assurance

Finally, if you hire a professional installer,make sure to establish a well-defined plan anda contract that clearly specifies responsibilitiesand pricing.

I M P L E M E N T I N G A C L O S E D C R A W L S P A C E

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S A M P L E D E S I G N S A N D C O N S T R U C T I O N P R O C E S S 25

Section 3

SAMPLEDESIGNS ANDCONSTRUCTIONPROCESSOverview

Advanced Energy has field tested severalclosed crawl space designs. This sectioncontains drawings for the designs that provedeffective for moisture control and that meet theminimum requirements of the North Carolinaresidential building code described in Section4. The numbered callouts refer to notes foreach of the specific components in thedrawing. This section also includesbackground information, advantages anddisadvantages for the two humidity controlstrategies used in the sample designs, as wellas a sample construction sequence based onprocesses Advanced Energy uses to haveclosed crawl spaces built in occupied homesfor field research projects.

The designs presented here are not the onlyclosed crawl space designs that are acceptable.They are simply examples that performedsuccessfully in the field testing detailed inSection 6. These designs have been utilized in

other Advanced Energy research projects andby professional installers in a variety oflocations in North Carolina. There are manyother designs that can perform acceptably andthat meet the requirements of the NorthCarolina residential building code.

The sample designs and process presentedhere are not definitive specifications. If you area builder, property owner, or other contractorplanning to install closed crawl spaces, you willneed to adjust these designs and processes toyour local site conditions, code requirements,home design, construction processes andoccupant needs to ensure success.

Recommended HumidityControl Methods

Some installers and researchers have theorizedthat the moisture control improvements ofclosed crawl spaces allow the mechanicalcontractor to down-size heating and coolingequipment. However, there are few commonlyavailable tools at the time of this writing tocalculate the impact of a closed crawl space onthe sizing of mechanical equipment for the home,and Advanced Energy research projects have notinvestigated this aspect of performance.

Recommendation 1Control humidity in the closed crawl spacewith dry air from the supply-side ductwork ofthe house air-conditioning system. Provide a

backflow damper (for example, a gravity-operated butterfly damper) and either abalancing damper or constant airflow regulatorto provide nominal airflow of 1 cubic foot perminute (0.5 liters per second) per 30 square feet(4.6 square meters). Traditional balancingdampers are adjustable over a range of flows.Constant airflow regulators provide a calibratedamount of flow without any need for adjustment.Multiple supply vents may be used to achievethe desired airflow and/or desired distribution ofair. If necessary, adjust the airflow to controlrelative humidity in the crawl space to thedesired level, typically 70% relative humidity orlower. Flow can be measured with a simple bag-fill method (for an example, see the Resourcesand References section under Canada Mortgageand Housing Corporation) an anemometer/digital air flow meter, a powered flow hood, or apassive flow hood. No return air vent is allowedwith this method.

Metal strapping holds this 4 inch (102 mm)diameter supply duct horizontal to ensureproper operation of the butterfly backdraftdamper. The balancing damper is visiblebehind the butterfly damper. The connectionto the supply trunk duct is sealed with mastic.

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S A M P L E D E S I G N S A N D C O N S T R U C T I O N P R O C E S S26

AdvantagesThis system is inexpensive, simple to install,fully adjustable, and has no need formaintenance beyond a periodic inspection. It isunlikely to be affected by the operation of otherexhaust fans in the house, including largeexhausts like clothes dryers. If the central airconditioner fails, the homeowner is likely torepair it, thus guaranteeing operation of thedrying mechanism for the closed crawl space.The lack of return duct or passive transfer grillfrom the crawl space to the house reduces thechance that the crawl space will affect theindoor air quality of the living space above.

DisadvantagesRelative humidity control appears to be lesseffective in the spring and fall when air-

conditioner use is lower. If the air conditioner isnot providing adequate dehumidification for theliving space, then it may not provide adequatedehumidification for the crawl space. Over-sizing the air conditioner or setting the systemfan to run after the air conditioner compressorhas stopped are bad strategies because theycan reduce the air conditioner’s ability todehumidify. Occupants can prevent the airconditioner from controlling humidity bygenerating excessive humidity in the house,choosing not to run the air conditioner, runningthe air handler fan continuously, and/or keepingwindows and doors open to outside duringhumid weather. The lack of return duct orpassive transfer grill from the crawl space to thehouse does not meet the requirements for an“unvented” crawl space specified in the 2004Supplement to the International Codes. SeeSection 4 for more details.

What about Pressure Effects?Theoretically, in a very tightly air-sealed house,operating the supply duct to the closed crawlspace with no return to the house could createa small negative pressure in the house withreference to outside or to the crawl space.Some of the air supplied to the crawl spacemight then return to the living space. InAdvanced Energy field tests, the small crawlspace airflow causes a negligible pressureeffect that is far exceeded by the effects of ductleakage, stack pressure or wind-inducedpressures in the building. Sealing floorpenetrations reduces the risk of crawl space airentering the living space. To help eliminate the

possibility of negative pressure, an outside airintake can be properly sized and installed inthe return side of the HVAC duct system. Insuch a system, the ventilation air slightlypressurizes the living space and then exitsthrough the building envelope. The crawl spacesupply makes use of some of the exiting

This 4 inch (102 mm) diameter constantairflow regulator (CAR) uses a pressure-modulated, flexible bladder to deliver aconstant rate of airflow over a wide range ofduct system pressures. The model showndelivers 30 cubic feet per minute (15 litersper second). Operation is completelypassive, with no electronic controls.

Schematic representation of crawl space duct systemwith integrated outside air intake and crawl spacesupply duct. Drawing provided by Indoor Environmental Systems, ©2005.

This outside air intake replaces a standard-size concrete masonry unit (CMU) block orfoundation vent and houses a washable filter.Photo credit: Indoor Environmental Systems.



ventilation air by using it to dry the crawlspace before it leaves the building. Section 6has details on how this system wasimplemented in Advanced Energy’s Princevilleresearch project.

Recommendation 2Control water vapor in the crawl space withone or more permanently installeddehumidifiers, each with a minimum 15 pint-per-day capacity. Adjust as needed to controlrelative humidity in the crawl space to desiredlevel, typically 70% or lower. Pipe condensateper local code requirement to outdoors or to aninterior pump that discharges to outdoors.Provide a dedicated, non-switched, GFCI-protected electrical outlet for the dehumidifier.

AdvantagesDehumidifiers are capable of rapidly removinglarge amounts of water vapor and areindependent of the house conditioning system.They can maintain lower relative humiditylevels than air conditioning equipment. Low-profile or horizontal-mount units are availableto accommodate short crawl spaces.

DisadvantagesDehumidifiers require periodic maintenanceand may not be noticed when they fail. Someunits must be re-activated manually after poweroutages. High-quality models can be

expensive. Condensate drains require periodicinspection and, if they fail, can allow liquidwater in the crawl space. There is currently nostandard protocol for calculating the requireddehumidifier capacity; manufacturers providegeneral sizing guidelines. Dehumidifier capacitydecreases as ambient temperature decreases, soperformance must be verified if dehumidificationis needed in the winter months.

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Sample Design: Supply Air andFloor Insulation

1. Seal exterior wall penetrations and matingsurfaces at top and bottom of sill plate andat top and bottom of band joist. Crawl space access panel(s) or door(s) must beair-sealed.

2. No open foundation vents are allowed inexterior walls. Openings to ventilated porchfoundations must be air-sealed with anaccess panel or permanent materials. Install flood vents per local residential codewhere required.

3. Slope finished grade away from building perlocal residential code or for 6 in. drop over10 ft. Provide a method to transport roofrunoff away from the house. Gutters anddownspouts are one such method.

4. Dampproof or waterproof the exterior wallsurface when the crawl space floor is belowexterior grade.

5. It is not necessary to provide a capillarybreak (mortar admixture or physical barrier)between the footings and foundation wallsor interior columns, but this may provideadditional moisture control.

6. Provide foundation drain to daylight perlocal residential code requirements.

7. Seal all plumbing, electrical, duct, cable,and other penetrations through the sub-floor with fire-stop materials and sealants.Fiberglass or rock wool insulation aloneare not sufficient.

8. Insulate floor joist cavities. Placeinsulation in full contact with the sub-floorand ensure that it is secured in place. UseR-value required by local residential code.

9. Leave a minimum 3” termite inspectiongap between the top of the wall vaporretarder and the top of the masonry wall.Seal the top of the vapor retarder to thewall with duct mastic or equivalent sealant.Optionally, apply a light colored paint orcoating over the inspection gap to improveinspectability by pest controlprofessionals.

10. Air seal all heating and cooling ductworkwith a duct mastic system. Install allductwork located in the crawl space withR-value per local code requirement.

11. Control moisture vapor in the crawl spacewith supply air from the house air-conditioning system. Set supply air volumeper local residential code requirement.Adjust as needed to control relativehumidity in crawl space to desired level.Provide a backflow damper and either abalancing damper or constant airflowregulator to control airflow. Multiple supplyvents may be used to achieve the desiredairflow and/or desired distribution of air. Noreturn air vent is allowed in the crawl space.

12. Terminate water heater drains,temperature/pressure relief pipes, and A/Ccondensate drains to outdoors or to aninterior pump that discharges to outdoors.Terminate all kitchen, bathroom andclothes dryer vents to outdoors.

13. Any fuel-fired furnaces, water heaters, orother appliance in a closed crawl spaceshould be of a “direct vent” or “two-pipe”design, meaning that all air for combustionis piped directly from outside to theappliance and all combustion exhaustgases are piped directly from the applianceto outside.

14. Cover 100% of the crawl space floor witha minimum 6-mil vapor retarder.Mechanically fasten and seal the vaporretarder material to the inside wallsurfaces, leaving the required termiteinspection gap at the top of the wall.Extend the vapor retarder up the interiorcolumns at least 4 inches above the crawlspace floor. Seal all seams and edges withfiberglass mesh tape and duct mastic orequivalent. Mechanically secure theground vapor retarder as necessary.

15. Grade the crawl space floor to one or morelow points. Provide crawl space drain(s) orsump pump(s) at lowest point(s). Slopedrains to daylight and include anaccessible backflow valve and 1/4-inchrodent screening. Gutter drains andfoundation drains (interior or exterior) mustnot be connected to the crawl space drain.



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Supply Trunk Duct

Advanced Energy Sample Design: A Closed Crawl Space With Supply Air and Floor Insulation

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Sample Design: Supply Air and Wall Insulation

1. Seal exterior wall penetrations and mating surfacesat top and bottom of sill plate and at top andbottom of band joist. Crawl space access panel(s)or door(s) must be air-sealed.

2. No open foundation vents are allowed in exteriorwalls. Openings to ventilated porch foundationsmust be air-sealed with an access panel orpermanent materials. Install flood vents per localresidential code where required.

3. Slope finished grade away from building per localresidential code or for 6 in. drop over 10 ft.Provide a method to transport roof runoff awayfrom the house. Gutters and downspouts are onesuch method.

4. Dampproof or waterproof the exterior wall surfacewhen the crawl space floor is below exterior grade.

5. It is not necessary to provide a capillary break(mortar admixture or physical barrier) between thefootings and foundation walls or interior columns,but this may provide additional moisture control.

6. Provide foundation drain to daylight per localresidential code requirements.

7. Seal all plumbing, electrical, duct, cable, and otherpenetrations through the sub-floor with fire-stopmaterials and sealants. Fiberglass or rock woolinsulation alone are not sufficient.

8. Insulate the crawl space wall over the wall vaporretarder material with rigid foam or other non-porous insulation material. Leave a minimum 3”termite inspection gap between the top of the wallinsulation and the top of the masonry wall. Leavea minimum 3” wicking gap between the bottomof the wall insulation and the crawl space floorsurface. Obtain R-value from local residentialcode. Ensure that the insulation complies withlocal residential code requirements forinstallation without a thermal barrier or ignitionbarrier. Insulate the band joist with batt insulationto facilitate removal and reinsertion during pestcontrol inspections. Ensure that batt facingscomply with local fire requirements.

9. Leave a minimum 3” termite inspection gapbetween the top of the wall vapor retarder and thetop of the masonry wall. Seal the top of the vaporretarder to the wall with duct mastic or equivalentsealant. Optionally, apply a light colored paint orcoating over the inspection gap to improveinspectability by pest control professionals.

10. Air seal all heating and cooling ductwork with aduct mastic system. Install all ductwork located inthe crawl space with R-value per local coderequirement.

11. Control moisture vapor in the crawl space withsupply air from the house air-conditioningsystem. Set supply air volume per localresidential code requirement. Adjust as needed tocontrol relative humidity in crawl space to desiredlevel. Provide a backflow damper and either abalancing damper or constant airflow regulator tocontrol airflow. Multiple supply vents may be

used to achieve the desired airflow and/or desireddistribution of air. No return air vent is allowed inthe crawl space.

12. Terminate water heater drains,temperature/pressure relief pipes, and A/Ccondensate drains to outdoors, or to an interiorpump that discharges to outdoors. Terminate allkitchen, bathroom and clothes dryer vents tooutdoors.

13. Any fuel-fired furnaces, water heaters, or otherappliance in a closed crawl space should be of a“direct vent” or “two-pipe” design, meaning thatall air for combustion is piped directly fromoutside to the appliance and all combustionexhaust gases are piped directly from theappliance to outside.

14. Cover 100% of the crawl space floor with aminimum 6-mil vapor retarder. Mechanicallyfasten and seal the vapor retarder material to theinside wall surfaces, leaving the required termiteinspection gap at the top of the wall. Extend thevapor retarder up the interior columns at least 4 inches above the crawl space floor. Seal allseams and edges with fiberglass mesh tape andduct mastic or equivalent. Mechanically securethe ground vapor retarder as necessary.

15. Grade the crawl space floor to one or more lowpoints. Provide crawl space drain(s) or sumppump(s) at lowest point(s). Slope drains todaylight and include an accessible backflow valveand 1/4-inch rodent screening. Gutter drains andfoundation drains (interior or exterior) must notbe connected to the crawl space drain.



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Sample Design: Dehumidifierand Floor Insulation

1. Seal exterior wall penetrations and matingsurfaces at top and bottom of sill plate andat top and bottom of band joist. Crawl space access panel(s) or door(s) must be air-sealed.

2. No open foundation vents are allowed inexterior walls. Openings to ventilated porchfoundations must be air-sealed with anaccess panel or permanent materials. Install flood vents per local residential codewhere required.

3. Slope finished grade away from building perlocal residential code or for 6 in. drop over10 ft. Provide a method to transport roofrunoff away from the house. Gutters anddownspouts are one such method.

4. Dampproof or waterproof the exterior wallsurface when the crawl space floor is belowexterior grade.

5. It is not necessary to provide a capillarybreak (mortar admixture or physical barrier)between the footings and foundation wallsor interior columns, but this may provideadditional moisture control.

6. Provide foundation drain to daylight perlocal residential code requirements.

7. Seal all plumbing, electrical, duct, cable,and other penetrations through the sub-floor

with fire-stop materials and sealants.Fiberglass or rock wool insulation aloneare not sufficient.

8. Insulate floor joist cavities. Placeinsulation in full contact with the sub-floorand ensure that it is secured in place. UseR-value required by local residential code.

9. Leave a minimum 3” termite inspectiongap between the top of the wall vaporretarder and the top of the masonry wall.Seal the top of the vapor retarder to the wallwith duct mastic or equivalent sealant.Optionally, apply a light colored paint orcoating over the inspection gap to improveinspectability by pest control professionals.

10. Air seal all heating and cooling ductworkwith a duct mastic system. Install allductwork located in the crawl space with R-value per local code requirement.

11. Control humidity in the crawl space withone or more permanently installeddehumidifiers, each with a minimum 15pint-per-day capacity. Adjust as needed tocontrol relative humidity in the crawl spaceto desired level. Pipe condensate per localcode requirement to outdoors or to aninterior pump that discharges to a drain oroutdoors. Provide a dedicated, non-switched, GFCI-protected electrical outletfor the dehumidifier.

12. Terminate water heater drains,temperature/pressure relief pipes, and A/C

condensate drains to outdoors or to aninterior pump that discharges to outdoors.Terminate all kitchen, bathroom andclothes dryer vents to outdoors.

13. Any fuel-fired furnaces, water heaters, orother appliance in a closed crawl spaceshould be of a “direct vent” or “two-pipe”design, meaning that all air for combustionis piped directly from outside to theappliance and all combustion exhaustgases are piped directly from the applianceto outside.

14. Cover 100% of the crawl space floor with aminimum 6-mil vapor retarder.Mechanically fasten and seal the vaporretarder material to the inside wallsurfaces, leaving the required termiteinspection gap at the top of the wall.Extend the vapor retarder up the interiorcolumns at least 4 inches above the crawlspace floor. Seal all seams and edges withfiberglass mesh tape and duct mastic orequivalent. Mechanically secure the groundvapor retarder as necessary.

15.Grade the crawl space floor to one or morelow points. Provide crawl space drain(s) orsump pump(s) at lowest point(s). Slopedrains to daylight and include an accessiblebackflow valve and 1/4-inch rodentscreening. Gutter drains and foundationdrains (interior or exterior) must not beconnected to the crawl space drain.



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Sample Design: Dehumidifier andWall Insulation

1. Seal exterior wall penetrations and matingsurfaces at top and bottom of sill plate and attop and bottom of band joist. Crawl spaceaccess panel(s) or door(s) must be air-sealed.

2. No open foundation vents are allowed in exteriorwalls. Openings to ventilated porch foundationsmust be air-sealed with an access panel orpermanent materials. Install flood vents per localresidential code where required.

3. Slope finished grade away from building perlocal residential code or for 6 in. drop over 10 ft.Provide a method to transport roof runoff awayfrom the house. Gutters and downspouts are onesuch method.

4. Dampproof or waterproof the exterior wall surfacewhen the crawl space floor is below exterior grade.

5. It is not necessary to provide a capillary break(mortar admixture or physical barrier) betweenthe footings and foundation walls or interiorcolumns, but this may provide additionalmoisture control.

6. Provide foundation drain to daylight per localresidential code requirements.

7. Seal all plumbing, electrical, duct, cable, andother penetrations through the sub-floor withfire-stop materials and sealants. Fiberglass orrock wool insulation alone are not sufficient.

8. Insulate the crawl space wall over the wall vaporretarder material with rigid foam or other non-porous insulation material. Leave a minimum 3”

termite inspection gap between the top of thewall insulation and the top of the masonrywall. Leave a minimum 3” wicking gapbetween the bottom of the wall insulation andthe crawl space floor surface. Obtain R-valuefrom local residential code. Ensure that theinsulation complies with local residential coderequirements for installation without a thermalbarrier or ignition barrier. Insulate the bandjoist with batt insulation to facilitate removaland reinsertion during pest controlinspections. Ensure that batt facings complywith local fire requirements.

9. Leave a minimum 3” termite inspection gapbetween the top of the wall vapor retarder andthe top of the masonry wall. Seal the top of thevapor retarder to the wall with duct mastic orequivalent sealant. Optionally, apply a lightcolored paint or coating over the inspection gapto improve inspectability by pest controlprofessionals.

10. Air seal all heating and cooling ductwork with aduct mastic system. Install all ductwork locatedin the crawl space with R-value per local coderequirement.

11. Control humidity in the crawl space with one ormore permanently installed dehumidifiers, eachwith a minimum 15 pint-per-day capacity.Adjust as needed to control relative humidity inthe crawl space to desired level. Pipecondensate per local code requirement tooutdoors or to an interior pump that dischargesto a drain or outdoors. Provide a dedicated,non-switched, GFCI-protected electrical outletfor the dehumidifier.

12. Terminate water heater drains,temperature/pressure relief pipes, and A/Ccondensate drains to outdoors or to an interiorpump that discharges to outdoors. Terminateall kitchen, bathroom and clothes dryer ventsto outdoors.

13. Any fuel-fired furnaces, water heaters, or otherappliance in a closed crawl space should be ofa “direct vent” or “two-pipe” design, meaningthat all air for combustion is piped directlyfrom outside to the appliance and allcombustion exhaust gases are piped directlyfrom the appliance to outside.

14. Cover 100% of the crawl space floor with aminimum 6-mil vapor retarder. Mechanicallyfasten and seal the vapor retarder material tothe inside wall surfaces, leaving the requiredtermite inspection gap at the top of the wall.Extend the vapor retarder up the interiorcolumns at least 4 inches above the crawlspace floor. Seal all seams and edges withfiberglass mesh tape and duct mastic orequivalent. Mechanically secure the groundvapor retarder as necessary.

15. Grade the crawl space floor to one or more lowpoints. Provide crawl space drain(s) or sumppump(s) at lowest point(s). Slope drains todaylight and include an accessible backflowvalve and 1/4-inch rodent screening. Gutterdrains and foundation drains (interior orexterior) must not be connected to the crawlspace drain.



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Sample Closed CrawlSpace ConstructionSequence

The sample process presented here is not adefinitive specification; it is based onrecommendations from professional installersas well as processes used by Advanced Energyto have installers construct effective closedcrawl spaces for several research projects. Ifyou are a builder, property owner, or othercontractor planning to install closed crawlspaces, you will need to adjust these designsand processes to your local site conditions,code requirements, home design, constructionprocesses and occupant needs to ensuresuccess. More specifically, this sampleprocess is geared towards low-volumeconstruction of closed crawl spaces in smallhomes with simple foundation plans. Builders of the more complex homes typicallyfound in mainstream residential constructionwill likely need to make significant changes tothis process, especially if they build in high volume.

Remember that long construction schedulesmake it much more difficult to managemoisture prior to the crawl space and housebeing dried in. Refer to the sidebar on longconstruction schedules in Section 2 foralternative strategies to implement a closedcrawl space in such cases.

This process covers steps directly related tothe crawl space installation. It does not attemptto cover other requirements like foundationreinforcement, framing anchors, or masonryspecifications.

Steps that are designed specifically toprovide moisture management during theconstruction process are indicated by theblue water drop.

Foundation Phase

1. Locate footings.

2. Locate crawl space drain(s) or sumppump(s).

3. Locate crawl space access(es).

4. Pour footings and build foundation wall,installing crawl space drain pipe(s) through wall.

5. For hollow masonry walls, either fill thecores of the top course of block with mortaror use solid cap block for the top course.

6. Whenever possible, make the interiorfinished grade equal to or higher than theexterior finished grade.

7. Grade the crawl space ground to slope todrain(s) or sump(s) location.

When using drain(s),

a. Install crawl space floor drain andbackflow valve.

b. Extend exterior portion of crawl spacefloor drain pipe to daylight andterminate with 1/4” rodent screening.

When using sump pump(s),

a. Excavate sump locations and protectfrom collapse.

8. Install exterior foundation drain system,separate from crawl space drain system.Extend foundation drain pipe to daylight.

9. Ensure that all penetrations in thefoundation wall are water tight. Applydamp-proofing or water-proofing onexterior of foundation wall, if applicable.

10. Place backfill against the foundationwall and grade to slope away from thefoundation as soon as possible.

11. Air seal all penetrations in the foundationperimeter wall.

12. Attach and seal wall vapor retarder materialto the perimeter wall with required termiteinspection gap. Extend the wall vaporretarder material approximately 12 incheshorizontally onto the ground. (Alternately,wall vapor retarder can be installed whenthe finished ground vapor retarder materialis installed.)



13. Attach and seal vapor retarder materialaround each of the interior piers, extendingup at least 4 inches above the crawl spacefloor. Extend the pier vapor retardermaterial at least 12 inches horizontallyonto the ground. (Alternately, this could bedone when the finished ground vaporretarder material is installed.)

14. Install wall insulation, if applicable, withrequired termite inspection gap at top andwicking gap at bottom.

15. Ensure that the top of the foundation wall issolid or can be air sealed.

Floor Platform Phase

16. Apply gasket or sealant between sill plateand top of foundation wall.

17. Build first floor platform. Apply sealant orgasket between band joist and sill plate.Apply sealant or gasket between band joistand subfloor.

18. Cover holes in subfloor that can leakwater into the crawl space.

19. Install temporary layer of minimum 4-mil polyethylene on crawl space ground assoon as possible. Puncture holes in thistemporary ground vapor retarder to allowstanding water to drain into the ground.Note that it may not be feasible to installthe temporary ground cover until after thehome is dried-in.

Main Construction Phase

20. Install and close the crawl spaceaccess door(s). Spring-loaded hingesand/or a locked latch can help to ensurethat the door stays closed. Ensure thatsomeone on site is responsible for keepingthe door closed as much as possibleduring the day and for locking the door atthe end of every day.

21. Ensure that roof runoff does not enterthe crawl space.

22. If drains are installed, ensure thatdrains remain clear. If sump pits areinstalled, remove water with temporarypumps if needed.

23. Install and run a temporary dehumidifierto maintain targets of <70% relative humidityor <15% wood moisture content. Thedehumidifier condensate must be drained orpumped to outside. Ensure that someone onsite is responsible for providing power to thedehumidifier and making sure thedehumidifier is safe from theft.

24. Finish all plumbing work in the crawlspace, including sump pumps anddehumidifier drain, if applicable.

25. Finish all electrical work in the crawlspace, including at least one permanentlywired, non-switched GFCI-protected outletto accommodate at least one permanent ortemporary dehumidifier.

26. Install crawl space supply air duct, ifapplicable.

27. Finish all other mechanical work in thecrawl space, including duct sealing andinstallation of outside air intake, ifapplicable. Ensure that vapor retardermaterial is installed under the air handlerunit(s) if the unit is to be installed in thecrawl space.

28. Ensure that clothes dryer vent, kitchenexhaust, bathroom exhaust, condensatedrains, and water heatertemperature/pressure relief all terminateoutside the crawl space.

29. Air seal all penetrations in the subfloor andband joist.

30. Install insulation in subfloor, if applicable.

After ALL CCrawl Space Work IsComplete

31. Remove temporary ground vapor retarderand all construction debris, wood forms, ororganic matter from the crawl space.

32. Install permanent ground vapor retardermaterial, overlapping the horizontal flap ofthe wall vapor retarder and any otherseams by at least 12 inches.

33. Secure the ground vapor retarder as desired.

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34. Seal all seams in the vapor retardermaterial with fiberglass mesh tape and duct mastic.

35. Confirm proper installation and operationof the crawl space drain.

36. Attach the permanent ground vapor retardermaterial to the crawl space drain(s) orsump pump(s).

37. If 6-mil unreinforced polyethylene is usedfor the ground vapor retarder, providereinforcing material along the paths to theair handler unit and any other equipmentthat will be serviced.

38. Install permanent dehumidifier, ifapplicable.

39. Confirm that the access door is weather-stripped, fits well, and can be latched.

40. Install a laminated sign inside the crawlspace access door to remind people tokeep the crawl space access door closedand maintain the integrity of the vaporretarder. The sign should also list thecomponents of the closed crawl spacesystem, any maintenance the componentsneed, and a phone number for questions.

41. Obtain Certificate of Occupancy andpermanent power connection.

42. Remove temporary dehumidifier, ifapplicable.

43. Activate permanent dehumidifier(s), ifapplicable.

44. Activate sump pump(s), if applicable.

45. Activate HVAC system, then set supply airflow rate, if applicable.

Post-Occupancy

Provide documentation of the intended level ofrelative humidity control to the property ownersand provide crawl space maintenanceguidelines as desired. See Section 2 for asample list of maintenance guidelines. If arelative humidity and/or liquid watermonitoring system is installed in the crawlspace, specify the conditions under which theproperty owner should contact the crawl spaceinstaller or builder for service or inspection.

At a later date, verify proper performance of allsystem components and adjust the supply airflow rate or dehumidifier setting, if necessary, tomaintain the intended relative humidity in thecrawl space. Some installers may want to re-inspect the system within a few weeks ofactivation. This inspection (or an additionalinspection) may be scheduled several monthsafter activation to verify performance in the humidspring or summer months. The inspection couldoccur as part of a contract installer’s qualityassurance program, part of a builder’s warrantyinspection processes, or as a response to theproperty owner’s monitoring of the system.


B U I L D I N G C O D E S 39

Section 4

BUILDING CODES

Historic Origins

Construction guidelines from agencies like theNational Bureau of Standards (1923) and theFederal Housing Administration (1935) containthe earliest known recommendations that crawlspaces be ventilated with outside air. Despitedocumented failure in such crawl spaces in the1930s and a lack of technical justification, theFHA turned these guidelines into requirementsin the early 1940s. Since then, buildingregulations across the United States haverequired ventilation of crawl spaces withoutside air. This history is documented byWilliam Rose (Davis, Warren and Rose, 2002)and shows that there is no scientific basis forcurrent crawl space ventilation requirements.

Building research from the 1970s onward hasdocumented that this ventilation may cause orcontribute to moisture problems instead ofpreventing them, and more recent buildingcodes like the 2000 and 2003 versions of theInternational Residential Code (IRC) haveincluded language to allow the construction ofcrawl spaces without ventilation openings tothe outside. Unfortunately, these more recentcodes still require ventilation with outside airas the default, and allow crawl spaces to beapproved without any ground vapor retarder.

The exceptions that allow closed crawl spacesare vague or incomplete and as a result arenearly impossible to follow or enforceconsistently. For example, IRC Section R408.2Exception 5 allows a closed crawl space ifthere is a ground vapor retarder, perimeter wallinsulation, and conditioned air, but it gives noguidance on how much conditioned air shouldbe supplied or acceptable methods forinjecting the air.

Other sections of the code are problematic fortechnical reasons. Exception 5 requires that theperimeter wall insulation be installed inaccordance with Section N1102.1.7. SectionN1102.1.7 requires the perimeter wallinsulation to extend downward from thesubfloor to the finished grade level and thenvertically and/or horizontally for at least anadditional 24 inches (61 cm). This is oftenreferred to as the “L-shaped” method ofinstalling insulation. This method is not viablein the Southeast for two reasons:

• First, the risk of insect pest damage is toohigh in the Southeast to deprive the pestmanagement industry of an inspection gapat the top of the masonry foundation walland convenient access to the sill plate forinspection or treatment whenever possible.Insulation in ground contact can increasethe risk of termite infestation.

• Second, the “L-shaped” installation methodis extremely impractical in terms of real lifeconstruction sequences, access, inspections,and potential pest treatments given currentlyavailable insulation materials.

The 2004 Supplement to the InternationalCodes retains the problematic insulationrequirement in the IRC (now sectionN1102.2.8) and in the International EnergyConservation Code (Section 402.2.8).However, the Supplement has significantlychanged Section R408 Under Floor Spaces inthe IRC. The exceptions noted above in SectionR408.2 have been deleted. A new section,R408.3 Unvented Crawl Space, has beenadded. This new section allows construction ofa crawl space with no ventilation openings tothe outside if (1) there is a sealed groundvapor retarder, (2) the perimeter walls areinsulated in accordance with SectionN1102.2.8, and (3) the crawl space is designedas a plenum or it is designed with either anexhaust ventilation system with an air pathwayto the common area or a conditioned airsupply with a return air pathway to thecommon area. There is no apparentcompliance pathway for a closed crawl spacethat is isolated from the living space or thatutilizes only floor insulation.

Revising the NorthCarolina Residential Code

The inconsistencies and omissions of thecurrent code demanded a substantial revisionin order to create a compliance path that canbe consistently followed and enforced for avariety of acceptable closed crawl spaces. Abroad group of stakeholders including code

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officials, pest management professionals,builders, building scientists, installers of closedcrawl spaces, and product manufacturers,worked with the North Carolina Building CodeCouncil and the code enforcement staff at theNorth Carolina Department of Insurance forover two years to craft this sorely-needed coderevision. The end result was an updated Section408 that governs wall-vented crawl spaces, anda completely new Section 409 that governsclosed crawl spaces. Requirements or optionswere added to the code when research or fielddata indicated that they perform as intended,and existing requirements were left in placeunless there was research or field data thatshowed they do not perform as intended.

The North Carolina Building Code Counciladopted the new crawl space code language inSeptember 2004 and the state of North Carolinaapproved it in November of 2004. This newcode was made available for reference as ofDecember 1, 2004 as an alternate to theexisting printed code, and the new code will beenforced in 2006 with the release of theupdated North Carolina Residential Code inprint. In some cases, local code officials mayrequire or accept a stamped letter of approvalfrom a registered professional engineer as analternate path for permitting and inspection.

Requirements of the New North CarolinaResidential Code This section provides a general overview of therequirements of the new code language for bothwall-vented and closed crawl spaces. Thissection is not a direct copy of the official codelanguage, and compliance with the items listedhere does not guarantee compliance with theresidential building code. Where there is anydifference between the items listed here and theresidential building code, the code languagetakes precedence. For links to online NorthCarolina code information, refer towww.crawlspaces.org.

All Crawl Spaces

Water drains (e.g. pressure relief,condensate lines, drain pans, etc.) shallterminate outdoors, to a crawl space floordrain, or to an interior pump and shall notintentionally discharge in the crawl space.

Dryer vents shall terminate outdoors.

The crawl space shall be separated fromadjoining basements, porches, andgarages by permanent walls. All utilitypenetrations shall be sealed.

Latched and weather-stripped doors oraccess panels shall provide accessbetween the crawl space and adjoiningbasements, porches, and garages.

A minimum 6-mil polyethylene vaporretarder or equivalent shall cover 100% ofexposed earth in the crawl space, withjoints lapped at least 12 inches (305 mm).

The floor of the crawl space shall begraded to one or more low spots, and adrain to daylight or a sump pump installedat each low spot.

Crawl space drains shall be separate fromroof gutter drain systems and foundationperimeter drains.

Where the outside grade is higher than theinside grade, the exterior walls shall bedampproofed from the top of the footing tothe finished grade as per section R406.1.

The building site shall be graded to drainwater away from the foundation per section R401.3.

All penetrations through the subfloor shall besealed with non-porous materials, caulks orsealants. The use of rock wool or fiberglassinsulation is prohibited as an air sealant.

All heating and cooling ductwork in thecrawl space shall be sealed with ductmastic or other industry approved ductclosure systems.

All organic material, vegetation, woodforms for placing concrete and otherconstruction materials shall be removedbefore the building is occupied or used forany purpose.

Buildings in flood-prone areas shall beprovided with flood openings in the crawlspace perimeter wall per section R327.2.2.

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Wall-vented Crawl Spaces

Minimum net area of ventilation openingsshall be 1 sq. foot (0.0929 sq. meter) per150 sq. feet (13.9 sq. meters) of crawlspace floor area. Minimum net area maybe reduced to 1/1,500 of the crawl spaceground area where the openings areplaced so as to provide cross-ventilation.

One vent shall be within 3 feet (914 mm)of each corner of the building. When thecrawl space is on a sloped site, the uphillfoundation walls may be constructed without wall vent openings to prevententry of rainwater.

Vent dams, to prevent entry of groundsurface water, shall be provided wheneverthe bottom of the foundation vent openingis less than 4 inches (102 mm) above thefinished exterior grade.

Insulation must be installed in the floor structure.

Closed Crawl Spaces

The crawl space perimeter wall shall be air-sealed.

Access panels or doors shall be tight-fitting, have a latch mechanism, and beinsulated to at least R-2

The minimum 6-mil polyethylene ground

vapor retarder may optionally be installedas a full interior liner by sealing the edgesto the walls and beam columns andsealing the seams. The top edge of such aliner shall terminate at least 3 inchesbelow the top edge of the masonryfoundation wall. The top edge of the linershall be brought up the interior columns aminimum of 4 inches above the crawlspace floor.

The ground vapor retarder may optionallybe protected against ripping anddisplacement by pouring a minimum 2inch thick, unreinforced concrete surfaceover the vapor retarder. Floor grading anddrain or sump pump requirements stillapply.

At least one of the following methods ofspace moisture vapor control shall beprovided, and combinations of multiplemethods are allowed:

Dehumidifier. A permanently installeddehumidifier shall be provided in thecrawl space. The minimum rated capacityper day is 15 pints (7.1 Liters).Condensate discharge shall be drained todaylight or interior condensate pump.Permanently installed dehumidifier shallbe provided with an electrical outlet.

Supply air. Supply air from the dwellingair conditioning system shall be ductedinto the crawl space at the rate of 1 cubicfoot per minute (0.5 L/s) per 30 squarefeet (4.6 sq. meters) of crawl space floor

area. No return air duct from the crawlspace to the dwelling air conditioningsystem is allowed. The crawl spacesupply air duct shall be fitted with abackflow damper to prevent the entry ofcrawl space air into the supply ductsystem when the system fan is notoperating. An air relief vent to theoutdoors may be installed. Crawl spaceswith moisture vapor control installed inaccordance with this section are not to beconsidered plenums.

House air. House air shall be blown intothe crawl space with a fan at the rate of 1cubic foot per minute (0.5 L/s) per 50 sq.feet (4.6 sq. meters) of crawl space floorarea. The fan motor shall be rated forcontinuous duty. No return air duct from thecrawl space back to the dwelling airconditioning system is allowed. An air reliefvent to the outdoors may be installed. Crawlspaces with moisture vapor control installedin accordance with this section are not to beconsidered plenums.

Exhaust fan. Crawl space air shall beexhausted to outside with a fan at the rateof 1 cubic foot per minute (0.5 L/s) per 50square feet (4.6 m2) of crawl space floorarea. The fan motor shall be rated forcontinuous duty. There is no requirementfor make-up air.

Conditioned space. The crawl spaceshall be designed as a heated and/orcooled, conditioned space with insulationon the perimeter wall. Intentionally

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returning air from the crawl space tospace conditioning equipment that servesthe dwelling shall be allowed. Foamplastic insulation located in a conditionedcrawl space shall be protected againstignition by an approved thermal barrier.

Closed crawl spaces used as supply orreturn air plenums for distribution ofheated or cooled air shall comply with therequirements of the N.C. MechanicalCode. Crawl space plenums shall notcontain plumbing cleanouts, gas lines orother prohibited components. Foamplastic insulation located in a crawl spaceplenum shall be protected against ignitionby an approved thermal barrier.

Fuel burning appliances located in thecrawl space such as furnaces and waterheaters shall obtain combustion air fromoutdoors as per the N.C. Mechanical Code.

The thermal insulation in a closed crawlspace may be located in the floor systemor at the exterior walls, with the exceptionthat insulation shall be placed at the wallswhen the closed crawl space is designedto be an intentionally heated or cooled, conditioned space.

Where the floor above a closed crawlspace is not insulated, the walls shall beinsulated. Wall insulation can be locatedon any combination of the exterior andinterior surfaces and within the structuralcavities or materials of the exterior crawlspace walls. Wall insulation systemsrequire that the band joist area of the floor

frame be insulated. Wall insulation shallbegin 3 inches below the top of themasonry foundation wall and shall extenddown to 3 inches above the top of thefooting or concrete floor, 3 inches abovethe interior ground surface or 24-inchesbelow the outside finished ground level,whichever is less. No insulation shall berequired on masonry walls of 9 inchesheight or less.

Other North CarolinaResidential Code Issues

Unregulated Specifications

The new code language does not specifyrequirements for every crawl space designelement. Such items will need to be specifiedby the designer.

Some examples are:

• Pitch of grade for the crawl space ground

• Size of crawl space drains

• Mechanical fastener schedules for wall vaporretarder or wall insulation

• Sump pump ratings

• Maximum air flow for the supply air drying method

• Methods of securing the ground vapor retarder

Fire Ratings for Foam Plastic Insulation

Changes awaiting adoption by the N.C. BuildingCode Council at the time of this writing willremove ASTM E84 as a stand-alone test toallow installation of foam plastic insulation incrawl spaces without a thermal barrier orignition barrier. The following methods ofcompliance will still be accepted: FM 4880, UL1040, ASTM E 152, UL 1715, or other testsrelated to actual end use configurations.

Pressure relief

The code language allows an air relief vent tothe outdoors when either house air orconditioned supply air is utilized to meet themoisture control requirement. Installing such arelief vent is not recommended by AdvancedEnergy, but if one is installed it shouldincorporate a backdraft damper to preventoutside air from flowing into the crawl space.

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Exhaust Fan Strategies Require Careful Design

The N.C. residential code allows the use of anexhaust fan to take air from the crawl spaceand reject it to the outside as an acceptedmethod for providing the required water vaporcontrol, with the assumption that the makeupair comes from the conditioned volume of thehouse above.

This method presents some risks. First, toavoid the risk of backdrafting any combustionappliances, don’t consider using exhaust fansin the crawl space unless all combustionappliances in the crawl space are direct vent(“two-pipe”) models, with all combustion airpiped directly from outside to the applianceand all combustion gases piped directly fromthe appliance to outside.

Second, there is no guarantee that the make-upair for the fan will come from the house asopposed to outside. The floor air sealing(which the code also requires) reduces the flowof makeup air from the house. House exhaustfans and “stack effect” – the natural action ofwarm air rising up and out of a home – canreduce air pressure in the house such that airwill not flow to the crawl space. When thishappens, the air removed from the crawl spaceby the exhaust fan is more likely be replacedby air from outside – exactly the situation theclosed crawl space is designed to avoid.

There are several scenarios which may requireyou to exhaust air from the crawl space,especially in existing homes. For example, youmay need to remove radon or other harmful soilgases, ensure isolation of crawl space air fromthe living space when there are environmentalhazards like mold or asbestos present, orsimply prevent objectionable crawl space odorsfrom entering the home. In these cases, providea designed source of makeup air (one examplecould be a second fan that injects house airinto the crawl space) to ensure that the crawlspace exhaust fan won’t create a combustionhazard or water vapor load.

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I M P R O V I N G W A L L - V E N T E D C R A W L S P A C E S 45

Section 5

IMPROVINGWALL-VENTEDCRAWL SPACESOverviewImproving a wall vented crawl space orconverting it to a closed crawl space canpresent choices and challenges that are notfound in new construction. This sectionfocuses on those challenges and does notrepeat the general design informationdiscussed in Section 1.

Converting a crawl space is much more than just closing the vents!

Cutting off the flow of outside air into the crawlspace is one of the key components of aproperly closed crawl space, but all the designelements from Section 1 are needed forsuccess. Simply closing the vents in anexisting crawl space will likely cause moisturelevels to increase and cause damage,particularly if there is exposed ground withouta vapor retarder. Just closing the vents can bedownright hazardous if there is combustionequipment located in the crawl space.Does thatmean there’s no middle ground between a wall-vented crawl space and a fully closed crawlspace with a sealed vapor retarder? No.

In existing homes, it can be acceptable toimprove the crawl space in steps. Besidesmoisture control and combustion safety,another reason to proceed carefully with aconversion is to avoid cosmetic damage in theliving area that can occur if the house is driedtoo quickly or if lack of attention during thedrying process results in more drying than isnecessary. For example, it is unlikely that woodframing ever needs to be dried below 12%moisture content, but unattended dehumidifierscould dry the wood well below this level andcause damage. However, if the home hasexperienced wet conditions for a long time, thematerials in the home will have stabilized at ahigh moisture content and some damage maybe unavoidable. As the crawl space is drieddown to acceptable levels, gaps may open inhardwood floors, wood trim carpentry, drywallsurfaces, or cabinetry in the living area. On theother hand, swollen or cupped wooden flooringmay flatten out again. Once installed, closedcrawl spaces stay drier than wall-vented crawlspaces in the summer and more humid in thewinter (see the Research Results for details),which will tend to reduce the range ofshrinkage and expansion of those materialsover time.

Steps for Improving aWall-vented Crawl Space

Step 1: Protect the crawl spacefrom water sources

At a minimum, wall vented crawl spaces need aground vapor retarder on 100% of the crawlspace ground, including steep-sloped earthenwalls. There should be no plumbing leaks, nointrusion of ground water, and no intrusion ofwater from outside. This may require:

• Adding a system to manage rain water,

• fixing leaking irrigation or sprinkler systems,

• blocking off low crawl space vents that allowrainwater to enter,

• reducing flooding potential by altering theexterior grade,

• sealing off below-grade holes,

• adding or repairing a foundation drainagesystem,

• adding or repairing foundationwaterproofing,

• fixing plumbing leaks,

• draining standing water, or

• adding an internal drain system or sump pump.

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Replace damaged or dirty, incomplete groundvapor retarders with a new vapor retarder thatcovers all soil and is secured to preventfuture movement or damage. All kitchen,bathroom, and clothes dryer vents mustterminate outside the crawl space. All airconditioner or dehumidifier condensate drainlines and water heater drains must terminateoutside the crawl space.

Step 2: Repair structural damage or rot

Eliminating all the sources of water listed inStep 1 will help to prevent rot from occurringin the future. If rot has occurred in the past oris ongoing, you may need to replace or repairstructurally damaged framing or flooring inconjunction with completion of Step 1. Ineither case, Step 1 must be completed toeliminate all the sources of liquid water thatcaused the rot in the first place.

At this point, cleaning up surface mold in thecrawl space is not worthwhile, since the airentering through the crawl space vents inspring and summer will make it possible formold to grow. If you continue to Step 5 andconvert the wall-vented crawl space to a closeddesign, then cleanup of surface mold growthcan be effective. See “Should I clean up themold?” in Section 7 for more details.

Step 3: Monitor for waterintrusion

Periodically inspect the improved wall-ventedcrawl space to ensure that all liquid waterproblems were successfully repaired in Step 1 and to ensure that no new problemshave occurred.

Even if all the water problems were properlyrepaired, you may still encounter smallpuddles of liquid water on the top of the newvapor retarder. Where ground water is notpresent, the ground vapor retarder can bepunctured to allow small puddles to drain intothe soil. This is acceptable because a smallhole lets liquid water drain out but only lets anegligible amount of water vapor diffuse intothe crawl space.

You might be wondering, “Where would thesesmall puddles come from after all the waterintrusion was fixed?” At this point, thefoundation vents that remain open will allowoutdoor air to enter the crawl space in thespring and summer, and the water vapor in thatair will condense on ductwork, water pipes, orother cool surfaces, drip down, and collect inpockets or low areas in the ground vaporretarder. (Refer to the Introduction for anexplanation of why this condensationhappens.) Note that operating the house at lowindoor temperatures in the summer acceleratesthis problem, especially when the ductwork isin the crawl space, by creating more coldsurfaces where condensation can occur. “Lowindoor temperatures” means thermostat

settings of less than 72° F/22° C in centralNorth Carolina, but could include warmersettings in extremely humid conditions likethose found in coastal environments.

Step 4: Isolate the crawl spacefrom the house

To reduce the chance that a damp crawl spacewill impact the living space above, sealpenetrations in the subfloor with fire-blockingmaterials and seal ductwork in conjunctionwith an overall assessment of air leakage andcombustion safety in the home by a qualifiedbuilding performance contractor. Sealingductwork also reduces the leakage of cold airinto the crawl space during air-conditioningperiods, which reduces the amount of coldsurface area that may experiencecondensation. For reference, see the appendix on duct sealing.

Step 5: Convert the wall-ventedcrawl space to a closed design

Once steps 1 and 2 are addressed, the crawlspace can be closed using the design andimplementation guidelines from Sections 1 and2, with these additional steps:

• Clean out debris. Remove any materials (e.g.cardboard, paper, etc.) that provide a foodsource for mold. Ensure that you remove any


I M P R O V I N G W A L L - V E N T E D C R A W L S P A C E S 47

existing vapor retarder before new materialis installed to avoid trapping water anddebris that will allow obnoxious molds orother organisms to grow. Remove rubble toprovide a smoother surface that is less likelyto damage the new vapor retarder material.Ensure that any hazardous contents (e.g.asbestos, gasoline, household chemicals,etc.) are properly handled and removed.Remove any other objects that will interferewith installation of the ground vapor retarder.Abandoned heating equipment and ductworkare common finds, but everything from oldtires and other trash to broken lawnequipment and children’s toys are found incrawl spaces.

• Replace damaged or contaminatedinsulation. Porous insulation that has beenwetted will likely not recover its rated R-value, even after it dries thoroughly. Supportsagging batt insulation in the floor structurewith tension wires (sometimes referred to as“tiger teeth”) so that the batts are incontinuous contact with the subfloor but isnot overly compressed. If there is so muchdamage that you want to replace all theinsulation, use either floor or perimeter wallinsulation as desired. If you chooseperimeter wall insulation, consult with yourpest management contractor to ensure thattreatments can continue and that the newinsulation will not void your insect pestwarranty or bond, if applicable.

• Provide a mechanism to control or detectliquid water problems. It may not be feasibleto correct interior grading or install gravitydrains in retrofit situations, like when thecrawl space or exterior grade is flat or in alow spot. In these situations, sump pumpsor liquid water alarm systems arealternatives.

• Provide adequate combustion air for gas- oroil-fired furnaces, water heaters or boilers.Without sufficient combustion air, theappliance can produce carbon monoxide orback draft.

A crawl space withatmospheric or “natural”draft equipment shouldnot be closed.

Ideally, any fuel-fired furnaces or waterheaters in a closed crawl space should beof a “direct vent” (often called “two-pipe”)design, meaning that all air for combustionis piped directly from outside into theappliance and all combustion exhaust gasesare piped directly from the appliance tooutside. Induced-draft combustion systemsmay be able to operate safely in a closedcrawl space with the installation of acombustion air injection system by aprofessional mechanical contractor. Thesystem must ensure adequate combustionair for the appliance, and installation shouldinclude pressure testing to verify properdraft in the combustion vent pipe andproper pressure in the combustionappliance zone with reference to outside.

• Be aware that objectionable odors maydevelop. Advanced Energy has received fivereports of strong ammonia-like odorsassociated with the drying-out of existingcrawl spaces in North Carolina, which maybe caused by the mold slowly dying orgoing dormant. The odors persisted forweeks or months without dissipating.Application of a fungicide in conjunctionwith reducing moisture levels has beenreported to eliminate this problem.

• Install a temperature and relative humiditymonitor in the repaired or converted crawlspace to verify that the improvements areeffective or to indicate the need foradjustments to the drying mechanism.Wireless sensors that display the crawlspace temperature and relative humidity on areceiving unit inside the house make it veryeasy for the homeowner or occupant tomonitor those conditions. Some of thesesensors include a user-adjustable alarm thatwill indicate when conditions exceed thedesired levels. See Section 8 for amanufacturer of such monitors.

• Decide whether or not to clean moldcontamination. Once the crawl space isproperly closed, cleaning up surface mold inthe crawl space can be effective since theimproved crawl space conditions shouldprevent mold growth from recurring. Ingeneral, it is not necessary to clean upmold, but there are a variety of reasons whyyou may want to do so. See “Should I cleanup the mold?” in Section 7 for more details.

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Basic Maintenance forCrawl Spaces

Most people don’t like to go into crawl spaces,but periodic inspection of any crawl spacehelps to ensure that any problems are caughtbefore they cause damage. Property owners canperform these inspections and basic maintenancechecks themselves or hire a private homeinspector or other contractor to do it for them.

Property owners should:

• Ensure that access doors are closed,especially during warm weather.

• Ensure that there are no solvents, gasolineor other potentially hazardous materials inthe crawl space.

• Inspect the crawl space regularly to:

❍ Identify vapor retarder damage or waterproblems. Note that small water leaks in acrawl space may not be caught by relativehumidity sensors.

❍ Ensure that no damage occurs when anycontractors work in the crawl space.

❍ Check and replace batteries as needed insensors or alarms.

• Ensure that any water intrusion, especiallyflooding, is quickly drained or pumped outof the crawl space.


R E S E A R C H R E S U L T S 49

Section 6

RESEARCH

RESULTS

Overview

By the late 1990s, concern over wall-ventedcrawl space moisture failures across thesoutheast had grown significantly amonghomeowners, builders, and building codeofficials. The need to quantify existingproblems and then compare and document theperformance of viable alternatives ledAdvanced Energy to conduct a study ofexisting homes and a controlled field study ofimproved homes. This crawl space project wasa multi-year effort to document how variouscrawl space ventilation and insulationstrategies affect moisture levels, energy use,and indoor air quality in real-world, occupiedhouses (Davis and Warren 2002). Anotherprimary goal of the research was todemonstrate practical, understandable closed crawl space construction techniquesthat can be transferred to mainstreamconstruction practice.

Co-funded by the U.S. Department of Energyand Advanced Energy, the project was directedby Bruce Davis of Advanced Energy andmanaged by Cyrus Dastur of Advanced Energyand Bill Warren of Bill Warren Energy Services.

The project advisory team includes Dr. AchillesKaragiozis, Oak Ridge National Laboratory; Dr. Wayne Thomann, Duke University; Dr. JohnStraube, University of Waterloo, Canada;Architect Bill Rose, University of Illinois atUrbana-Champaign; Dr. Joe Lstiburek,Building Science Corp.; Physicist AntonTenWolde, U.S. Forest Products Laboratory;and Environmental Scientist Terry Brennan,Camroden Associates. Vital support has been provided by the N.C. Solar Center, inRaleigh, N.C. and Southface North Carolina inBoone, N.C.

Advanced Energy is by no means the firstgroup to investigate the moisture performanceof wall vented crawl spaces. Rose (1994) wrotea review of crawl space investigation andregulation through history. Rose and TenWolde(1994) wrote a symposium summary paper toreview many of the issues associated with wallvented crawl space construction. The abovematerial, along with that of several others, isincluded in Recommended Practices forControlling Moisture in Crawl Spaces,ASHRAE Technical Data Bulletin, volume 10,number 3. Additionally, during the first year ofthe study Rose contributed an update of thehistorical review of crawl space regulation aspart of a technology assessment report (Daviset al. 2002). These articles reference a widerange of the authors and activities over theyears that built the understanding of wallvented crawl space moisture problems and solutions.

The field study has operated since the summerof 2001, but here we are reporting findingsfrom the experimental setup used from thesummer of 2003 through the summer of 2004,which is the basis for the design samples inSection 3. The complete technical reports thatare the basis for this section are availableonline at www.crawlspaces.org.

Quantifying ExistingCrawl Spaces

The characterization study examined tenhouses, from 2 to 9 years old, with wall-ventedcrawl spaces in the Piedmont (central) regionof North Carolina. A variety of instrumentationand first hand observation techniques wereused to describe the moisture, thermal, andindoor air quality performance of each house.These techniques included:

• homeowner interviews,

• detailed measurements of the home, crawlspace and surrounding property,

• surveys of moisture content, mechanicalequipment, insulation quality, and moistureproblems in the crawl space,

• bioaerosol sampling and analysis of totaland viable spore counts, and

• detailed air leakage testing to quantifyleakage through the supply ductwork, return

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ductwork, floor plane, and wall-ceilingplanes; and detailed logging of mechanicalsystem pressure effects.

Findings revealed that all ten crawl spaces hadmultiple moisture problems, unexpectedly highlevels of respirable, viable mold spores, andcompromised thermal performance due to poorinsulation performance and excessive shell andduct leakage.

Only two houses had a complete ground vaporretarder, and these homes suffered fromrainwater intrusion and condensation on theductwork, with visible mold covering most ofthe wood framing. Three homes had no groundvapor retarder at all.

These findings confirmed the theory that wallvented crawl spaces as they are currentlydesigned and built are not sufficient to controlmoisture acceptably in the North Carolinaclimate. Furthermore, all ten houses hadsignificant air leakage pathways measuredacross the floor system that separates the crawlspace air from the house air. Leakage from thecrawl space represented almost 19% of thetotal leakage of the house. Of that 19%, 44%was leakage through the duct system. Thisshowed that the crawl spaces are not wellisolated from the living space above, socontaminants from the crawl space are likely to affect the living space.

Field Study Experimental Setup

In addition to the 10-house characterizationstudy, this project studied 12 homes withimproved crawl spaces to identify solutions tothe moisture problems. These 12 homes,located in Princeville, North Carolina, are alllocated in the same development. Six housesare built side-by-side on each side of onestreet. All are the same size at 1,040 squarefeet, with the same floor plan and windowschedule. The development was built onseveral feet of controlled fill soil to elevate itand reduce the potential for future flooddamage. This added to the uniformity of thesite soil conditions, and the site was graded toprovide proper drainage.

The study homes are broken into three groupsof four homes each: one control group and twoexperimental groups. We reduced duct leakageand house leakage to comparable levels acrossall the groups. Average duct leakage variesfrom 51 to 68 CFM25 for these groups, whichrepresents rates of 5% to 7% of floor area.Dividing the duct leakage by the conditionedfloor area lets us use a consistent target acrossmany different sizes of home. Typical ductleakage for homes in North Carolina isupwards of 15%. Ideally, duct leakage wouldbe 3% or less. Average envelope leakage forthe study houses varies from 0.22 to 0.27CFM50 per square foot of envelope area.Typical house leakage for homes in NorthCarolina is roughly 0.35 CFM50 per square

foot envelope area, which is the same asAdvanced Energy’s standard house leakage target.

Floor and ceiling insulation deficiencies werecorrected in all houses, and all 12 homes havethe same make and model of packaged-unitheat pump. The ARI rated capacity of the heatpump is 22,000 BTU/hr. with efficiencies of10.0 SEER and 6.8 HSPF. Heat pumprefrigerant charge and system airflow weremeasured and corrected as needed in allhouses. All the houses have an outside airventilation intake integrated with the HVACductwork. A six-inch insulated flex duct fromoutside routs air through a one-inch pleatedmedia filter and then connects directly to thereturn plenum. Whenever the HVAC system isoperating, 40 cfm of filtered outside air ismixed into the return air stream, conditioned,and then distributed to the house. No fan-timing or fan-cycling controls are used in themechanical system.

The four control houses have conventionallyvented crawl spaces, with eleven 8” x 16”foundation vents. Each house has a six-milpolyethylene ground cover that is mechanicallysecured to the soil with turf staples. The seamsare lapped approximately six inches but are notsealed. The ground cover extends completelyto the foundation wall and intermediate piers,covering 100% of the soil. Although thebuilding code allows a reduction in the amountof wall venting when a ground vapor retarder ispresent, all 11 foundation vents were retained.(Note that the North Carolina code in place at



the time of construction (the 2000 InternationalResidential Code) does not require the groundvapor retarder since these vents provide the netfree area to meet the 1:150 ventilation-area tocrawl-space-area requirement). The floors ofthe control houses are insulated with well-installed R-19 Kraft-faced fiberglass batts.

The crawl space vents of the experiment homeswere sealed with rigid polystyrene foam andduct mastic or spray foam. Each of theseclosed crawl spaces has a sealed, six-milpolyethylene liner covering the floor andextending up the foundation wall, stoppingthree inches from the top of the masonry toprovide a termite inspection gap. The seams ofthe liner are sealed with fiberglass mesh tapeand duct mastic, and the edges are sealed withduct mastic and mesh tape to the foundationwall or intermediate piers. The liner ismechanically secured to the soil with turfstaples and to the foundation wall with afurring strip.

Mechanical drying in the closed crawl spacesis provided by a 4-inch duct that provides 35cfm of conditioned air to the crawl space fromthe supply plenum whenever the air handler isrunning. As designed, the extra air simplyexfiltrates through the crawl space perimeterwall. No fan-timing or fan-cycling controls areused in the mechanical system, and no stand-alone dehumidifiers are used for moisturecontrol. A balancing damper permitsadjustment of the flow, and a back-flowbutterfly gravity damper with a non-metallic

hinge prevents movement of air from the crawlspace into the supply plenum when the system is off.

Four of the closed crawl spaces are insulatedwith R-19 Kraft-faced fiberglass batts in thefloor, with the Kraft facing in contact with thesubfloor, and the other four are insulated with2 inches of R-13 foil-faced polyisocyanuratefoam on the perimeter wall and on the bandjoist. This closed-cell foam was installed witha three-inch gap between the top of the foamand the bottom of the sill plate to allow formonitoring of termite activity, and there is asecond gap at the bottom of the foaminsulation to prevent ground contact andwicking of moisture into the foam insulation.This foam meets the ASTM E84 and FactoryMutual FM 4880 requirements of the 2000International Residential Code for installationwithout a thermal barrier.

The ground vapor retarder is attached to theinside surface of the foam insulation with tapeor fiberglass mesh tape and duct mastic. Wespecifically did not install the wall insulation inthe IECC-required form, which specifies wallinsulation down to 24 inches below outsidegrade or horizontally on top of the soil in fromthe foundation wall for 24 inches. Instead, thebottom edge of the crawl space wall insulationwas only 3 to 6 inches below outside soilgrade level.

Instrumentation andData Collection

We recorded outside air temperature andmoisture content using three battery-operateddata loggers distributed across thedevelopment in locations shielded from rainand direct sun. We used the same type oflogger to record conditions inside each houseand inside each crawl space. Measurementswere recorded at 15-minute intervals. Thehouse data logger was placed at the center ofthe house in the HVAC return closet and twologgers (one extra for redundancy) werelocated together in the center of the crawlspace on the support beam for the floor joists.

We measured wood moisture content on a 60-day interval at ten locations in each crawlspace, including sill plate, band joist, floorjoist, center beam, and subfloor readings.

After seeing the potential for energy savingsduring a billing analysis in early 2003, weoutfitted all 12 houses with electricity sub-meters to record exact energy consumption byeach home’s package-unit heat pump system.The whole-house meter and sub-meters areread monthly.

The crawl space experiment has beenmonitored for more than three years at the timeof this writing. Ongoing measurements clearlyindicate that the closed crawl spacesconsistently outperform the wall-vented crawlspaces in terms of both moisture control and

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energy use, and here we’ll present a cross-section of findings from a one-year periodranging from the summer of 2003 through thesummer of 2004.

Moisture Performance

The closed crawl spaces in this project performnotably better than the vented crawl spaces withregard to relative humidity, absolute moisture(presented for convenience as dew pointtemperature), and wood moisture content,which are summarized in the figures below.

Daily average relative humidity in the closedcrawl spaces began a steady decline throughthe humid 2003 summer season as soon as thecrawl space supply duct was opened and theaccess door closed.

As fate would have it, 2003 was the wettest yearin recorded history in this part of NorthCarolina, while 2002 was a record-settingdrought year. The table below compares thepercent of time in each summer that thedifferent crawl spaces had a daily averagerelative humidity above the given thresholds:

The closed crawl spaces provided far betterperformance under the harshest conditions thanthe vented crawl spaces did under even themildest conditions. These results highlight thefact that even a carefully installed andmaintained ground vapor retarder covering100% of the soil is not sufficient to control

relative humidity levels in a wall-vented crawlspace, even with excellent exterior drainage.Well-constructed, extensively wall-vented crawlspaces without water intrusion and with a 100%ground vapor retarder may prevent wood rot in

crawl spaces, but water vapor control would beeven worse in typical vented crawl spaces giventhe usual poor quality of ground vapor retarderinstallation and maintenance in generalconstruction.

Crawl Space and Outdoor Relative Humidity

20

30

40

50

60

70

80

90

100

Jun-03 Jul-03 Aug-03 Aug-03 Sep-03 Oct-03 Nov-03 Dec-03 Jan-04 Feb-04 Mar-04 Apr-04 May-04 Jun-04 Jul-04 Aug-04

Wall Vented Closed Outside

Rela

tive

Hum

idity

(%)

Summer (June-August) Relative Humidity Summary2002 2003 2004

RH Threshold Vented Closed Vented Closed Vented ClosedAbove 90 % 0% 0% 23% 0% 7% 0%Above 80 % 39% 0% 86% 0% 70% 0%Above 70 % 79% 0% 98% 5% 92% 0%Above 60 % 94% 0% 100% 64% 100% 13%Above 50 % 100% 100% 100% 100% 100% 100%



The dew point temperature graph shows thatthe outside air contains more water vapor thanthe air in the wall-vented crawl spaces duringthe warm season, actually adding water vaporinstead of providing drying potential. Considerthis: the average dew point of the outside air atPrinceville during the summer of 2003 was73° F (23° C). This corresponds to conditionsof 88° F (31° C) and 60% relative humidity.When that air goes into the crawl space andencounters anything cooler than 73° F, therelative humidity peaks at 100% and the watervapor in the air can condense on that object.Supply ducts (55-65° F, 13-18° C), waterpipes and tanks (55-65° F), and even the floorof the crawl space (65-70° F, 18-21° C) andthe wood framing above (70-78° F, 21-26° C)can experience this condensation, especially ifthe homeowners condition their house totemperatures below 72° F (22° C). Even ifconditions aren’t bad enough for condensation,the relative humidity of the air entering thecrawl space will still easily reach levels of 90%or higher for prolonged periods of time.

The dew point measurements also highlight thefact that the closed crawl spaces stay morehumid than the wall-vented crawl spaces inwinter, further reducing the moisture swingseen by the house over the course of the year.This can in turn reduce the likelihood ofcommon cosmetic problems like shrinking andswelling of hardwood floors and wood trim, orcracking and “nail pops” in drywall.

Crawl Space and Outdoor Dew Point Temperature

15

25

35

45

55

75

Jun-03 Jul-03 Aug-03 Aug-03 Sep-03 Oct-03 Nov-03 Dec-03 Jan-04 Feb-04 Mar-04 Apr-04 May-04 Jun-04 Jul-04 Aug-04

Dew

Poi

nt (F

)

Wall Vented Closed Outside

65

Average Wood Moisture Content

6.0

8.0

10.0

12.0

14.0

16.0

18.0

Aug 2003 Oct 2003 Dec 2003 Feb 2004 Apr 2004 Jun 2004

Woo

d M

C (%

)

Vented + R-19 Floor Closed + R-19 Floor Closed + 2'' Foam on Wall

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The average wood moisture content graphshows readings for the three types of crawlspaces. The fact that the average woodmoisture content in the framing lumber in theclosed crawl spaces stays below 12% isnotable, not only because it reduces thelikelihood of surface mold growth but alsobecause wood this dry is less attractive totermites and very inhospitable to Southeasternspecies of wood-boring beetle pests. Woodmoisture content in the wall vented crawlspaces is much lower than is found in typicalexisting crawl spaces, showing the beneficialimpact of the 100% ground vapor retarder andproper site water management.

Temperature Conditions

Warmer temperatures in closed crawl spacesduring the winter months and the absence ofopen vents reduce the risk of intermittentfreeze damage to pipes or appliances in theclosed crawl space during sub-freezingweather, especially in windy conditions.

Energy Performance

Going beyond initial expectations, the closedcrawl space homes exhibited clear andsignificant energy savings over the controlhouses. This is true even for the four closed

crawl space houses with wall insulation thatincluded a termite inspection gap and did nothave insulation installed down 24” below gradeor 24” horizontally onto the crawl space floor,as is required by energy codes.

Energy used for heating and/or cooling for theaverage house in each group is shown in the“Average Seasonal HVAC Use per House” chart.The percentage of savings as compared to thecontrol houses is reported in the inset table.

For the 12 months analyzed, the floor-insulatedclosed crawl space houses used an average of15% less energy for space conditioning thanthe control houses, which represents a savingsof approximately 870 kWh (or roughly $87) peryear for each household.

The wall-insulated closed crawl space housesused on average 18% less energy than thecontrol houses over the same 12-monthperiod, which represents a savings ofapproximately 1025 kWh (or roughly $103) per year for each household.

Factors Affecting Energy Use

While we controlled the variables of climate,site drainage, architecture, insulation, shellleakage, duct leakage, and mechanicalequipment performance, there remainvariations in base load consumption andoccupant thermostat settings among thegroups that may be significant due to the small sample size.

Average Daily Crawl Space and Outside Temperatures

20.0

30.0

40.0

50.0

60.0

70.0

80.0

Jun-03 Jul-03 Aug-03 Sep-03 Oct-03 Nov-03 Dec-03 Jan-04 Feb-04 Mar-04 Apr-04 May-04DateVented + R-19 Floor Closed + R-19 Floor Closed + 2'' Foam on Walls Outside

Tem

pera

ture

(F)



We did not sub-meter the appliance, lighting,water heating or exhaust fan loads, but notedthat the total base load use in the controlhomes was significantly higher (10-20% inany given month) than that of the experimenthomes over the entire year. By luck of the draw,the control homes had higher occupancynumbers and greater numbers of childrenrelative to the experiment houses. The extraoccupant and base load in the controls wouldtheoretically increase the need for cooling inthe summer and decrease the need for heatingin the winter. The difference in base load usagebetween the controls and the floor-insulated

experiment houses is about the same in bothsummer and winter, which suggests that thesurpluses offset each other in terms of heatpump energy used/saved in the control housesto compensate for the difference. However,there is a greater difference in base loadconsumption between the control houses andthe wall-insulated experiment houses in thesummer than there is in the winter, whichmakes the summertime wall-insulated houseperformance look better.

Impact of Moisture Load onComfort and Energy Use

A review of the interior house data indicatedthat the control houses were operated 1° to 2° F cooler than the experiment houses in thesummer of 2003 and 1° to 2° F warmer thanthe experiment houses in the winter of 2003-04. This behavior could account for a portionof the energy savings we recorded, or it couldbe another indicator of the moisture benefits ofthe closed crawl spaces, since humidity levelsplay a large role in occupant comfort and thedata shows that the dew point temperatures inall the homes were very consistent.

We have not administered a formal survey ofoccupant comfort, but had an experience thatindicated the impact of crawl spaceperformance on occupant thermostat settings:in June of 2004 we upgraded three of the fourwall-vented control crawl spaces to test a newversion of closed crawl space. We installed acrawl space supply duct to providesupplemental drying, as was done in the otherclosed crawl spaces. When we returned to thesite four days later, one resident (who rarelyadjusts her thermostat) excitedly let us knowthat the night after we closed her crawl space,she turned up her thermostat because she felttoo cold in the house. This anecdotal evidencesuggested that the difference in indoor setpoint temperatures may not be a simple matterof homeowner preference that reduces themeasured energy savings, but instead be aresult of the improved performance of theclosed crawl spaces which deserves more

Average Seasonal and Annual HVAC Use per House

0

1

2

3

4

5

6

7

Summer(Jun-Aug '03)

Fall(Sep-Nov '03)

Winter(Dec '03-Feb '04)

Spring(Mar-May '04)

Annual

Thou

sand

skW

h

Wall-Vented Closed + R-19 Floor Closed + R-13 Wall

Savings Closed withR-19 Floor

Closed withR-13 Wall

Summer -22 % -36 %

Fall -5 % -10 %

Winter -10 % +4 %

Spring -19 % -28 %

Annual -15 % -18 %

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detailed investigation. Subsequently, in Julyand August of 2004, the occupants of the threeupgraded crawl space homes operated theirhomes within an average of 0.5 degrees of thetemperatures in the other closed crawl spacehomes, while the occupants of the lastremaining wall-vented crawl space homecontinued to operate their house an average of2 degrees cooler than the occupants in theclosed crawl space homes.

Radon Measurements

To ensure that these closed crawl spacedesigns were not negatively impacting thehealth of the homeowners with regard to radonexposure, we conducted radon monitoring inthe crawl spaces and the living areas from thesummer of 2003 to the summer of 2004.

According to the EPA’s “A Citizen’s Guide toRadon” homes should be remediated whenradon levels are above 4 pCi/L. One shouldconsider fixing the home when levels arebetween 2 and 4 pCi/L. Reducing radon levelsbelow 2 pCi/L is difficult.

The measured 2003-04 long-term resultsindicate slightly higher average concentrationsin the closed crawl spaces, with measurementsaveraging 0.5 pCi/l in the vented crawl spacesand 1.1 pCi/l in the closed crawl spaces. Theradon measurements in the living space do notshow a difference correlated with foundationtype; all houses average approximately 0.5 pCi/l with a maximum reading of 0.7 pCi/lin any house. The three highest crawl spacemeasurements all occurred in closed crawlspaces, with values of 2.0, 1.5 and 1.4 pCi/L.All other measurements were below 1.0 pCi/L.

While the crawl space levels were all below theEPA action threshold, the higher measuredradon levels do appear to correlate to theclosed crawl spaces. Advanced Energyrecommends treating closed crawl spaces likea short basement with regard to radon testingand mitigation. If the closed crawl space isbeing built in a radon risk area, the samemeasures used for radon assessment andcontrol with a basement or slab foundationare applicable.

Mold Sampling Results

Anderson samplers were used to measureviable spores in the crawl spaces, outside, andin the living spaces in 2001 and 2002.Measurements in the living spaces weresignificantly lower than the outsidemeasurements, but measurements in the livingspace above two of the wall-vented crawlspaces were the highest of the group.

Total spore counts, measured with Burkardsamplers, were significantly higher in the wall-vented crawl spaces than in the closed crawlspaces, but large numbers of mold sporeswere measured in all the crawl spaces duringthe first round of sampling in 2001. Generally,viable and total spore counts as high as weremeasured in this project are found only in thepresence of very large sources – e.g.harvesting fields, contaminated rooms, orcomposting facilities.

Princeville 2003-04 Radon Levels

0

0.5

1

1.5

2

2.5

3

3.5

4

House Crawl

Rado

n (p

Ci/L

)

Vented Closed



In the case of these crawl spaces, there weretwo contributing factors. First, the surroundingarea was deluged by heavy rains shortly beforethe samples were made. This is reflected inboth the crawl space and outdoor air data.Second, the sampling procedure required thetechnician to enter the crawl space, stirring upsettled dust, and this likely contributed to thesampled levels being as strikingly high as they were.

In subsequent testing, we inserted the samplerinto the crawl spaces on a long cantilever sothat the technician would not have to enter andstir up settled dust. These readings were in factmuch lower than the initial samples. After thecantilever sample was complete, we verified theimpact of entering the crawl space by having atechnician crawl inside the crawl space andtake a followup sample. These followupsamples, whether in the closed or wall-ventedcrawl spaces, showed a large increase inairborne spores. Most importantly, thesefindings point to the need to wear respiratoryprotection in all crawl spaces, even if there isno visible mold.

See Section 7 for background information onmolds and health impacts of mold exposure.

Research Implications

The Princeville field demonstration project isscheduled to conclude in April of 2005. Duringthe winter of 2004-05 Advanced Energy willtest a new crawl space configuration to assessthe energy impact of a 24-inch wide strip of R-10 foam insulation installed horizontally onthe ground of the wall-insulated, closed crawlspace houses. Final results and additionalanalysis will be posted on the project website,www.crawlspaces.org.

The performance improvement shown by theclosed crawl spaces is impressive, especiallyconsidering that the control houses likelyrepresent the best possible performance ofwall-vented crawl spaces. The vast majority ofnewly built wall-vented crawl spaces are notinstalled or maintained to the standards usedfor this project.

We believe the findings of this study willtransfer well to houses of similar geometry and geography to the study homes. However,additional consideration and study are requiredfor houses in other locations and with differentgeometry. The energy results seem to indicatethat wall-insulated closed crawl spaces willperform best in cooling-biased climates whilefloor-insulated closed crawl spaces will performbest in heating-biased climates. Of course,these homes have shallow foundations, and wehave not tested crawl space foundations withdeeper footing depths such as may be foundfarther north. A wall insulation strategy mayalso prove to perform best in such houses.

We won’t know with any certainty how well theimprovements in moisture and energyperformance will transfer to houses in otherclimates until a number are actually constructedand monitored. Advanced Energy has begun anew project to gather that data in multipleclimate zones while demonstrating the ability ofthe production housing market to incorporateclosed crawl space technology into itsconstruction processes.

Currently we find that the energy benefits ofclosed crawl spaces are not accurately predictedby popular energy analysis software, so it maybe some time before closed crawl spaces gettheir due respect when builders are choosinghouse specifications aimed at achieving acertified minimum energy rating. Future researchwill include a detailed analysis of a variety ofsoftware tools, with the goal of identifyingimprovements needed in the tools and toreinforce the finding that consumers can improvethe efficiency of their homes by building orretrofitting a properly closed crawl space.

Two of the field study homes were highlyinstrumented and monitored by Oak RidgeNational Laboratory (ORNL) throughout theduration of the field study. The data collectedfrom these houses has been used to calibrateand validate a computer-based hygrothermalmodeling software tool. This software tool cannow predict the hygrothermal performance ofdifferent crawl space designs when given basicthermal and moisture characteristics of thematerials to be used in the design, along withenvironmental conditions.

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58


C O M M O N Q U E S T I O N S A B O U T M O L D 59

Section 7

COMMONQUESTIONSABOUT MOLDThis section summarizes detailed moldinformation that is presented in several of thetechnical references, specifically ACGIH, 1999;Davis, 2002; Burge, 2004; Fallah, 2004 andBrennan, 2005. In addition, we offerrecommendations based on Advanced Energyresearch findings and building investigations.

What is Mold?

Mold, together with mushrooms, bracket fungi,and puffballs are classified as fungi. Theseorganisms consist of a mat of hair-like strandscalled hyphae that form both the main bodyand fruiting bodies that make spores. Sporesare essentially baby fungi with a lunch box.Mushrooms, puffballs, and bracket fungi havelarge, easily seen fruiting bodies, while moldshave tiny fruiting bodies that are visible as asurface discoloration only when there are manyof them. Mold coverage ranges from lightspotting to thick blooms that cover large areas.They can range in color from black to green towhite, yellow and red and be present asdiscrete speckles or large fuzzy masses.

Mold reproduces by sending microscopicspores sailing on the air or floating on water.Mold spores are typically in the range of 3 to 40microns in size; for reference, a human hair istypically 100 to 150 microns in diameter. Asmall colony may release millions of spores.When it is above freezing, a sample of outdoorair almost anywhere in the United States is likelyto contain hundreds or thousands of moldspores per cubic meter. Consequently, almostall environmental surfaces have spores attached– it is virtually impossible to avoid them.

In order to sprout and grow into a colony, mostspores need to be in a location that providesoxygen, liquid water and/or relative humiditygreater than 70%, a source of carbon, andtemperatures between 45° F (7.2° C) and 100° F (37.8° C). Once most molds havegerminated, they do not need liquid water tocontinue growing. Unfortunately, theseconditions are found in nearly every wall-vented crawl space in the southeast for muchof the year. Because crawl spaces havenumerous air path connections to the housevia plumbing penetrations, electricalpenetrations, leaky ductwork, and more, wecould say that the crawl space is “MADD” – aMold Amplification and Delivery Device.

Because spores, carbon sources, warmth, anddark spaces are found in all houses, the onlyrealistic strategy for controlling mold growth isto control moisture levels. Eliminating liquidwater is the first step. Controlling relativehumidity is the second step and fortunately,most people are more comfortable at relative

humidity levels below the 70% thresholdrequired by most molds.

Hyphae exude enzymes that may decomposeorganic materials so the nutrient can beabsorbed into the hyphal mat. That, in fact, istheir ecological job – to decompose deadplants and animals. Molds are essential to theproper workings of the natural world.

Most molds are not good at digestingcellulose. Wood decaying fungi (soft rot, white rot, or brown rot) are the organisms thatactually decompose solid wood, and theygenerally require very wet wood with amoisture content of 30% or more. Soft rotrequires the continual presence of liquid water.Brown rot usually occurs on wood in contactwith damp soil or a continuous water source,but can also be caused by molds that transportmoisture from some other location (this lattertype is typically referred to as “dry rot”). Crawl spaces with long-term condensation,standing water, or exposed soil are vulnerableto any of these molds, especially at lowtemperatures caused by air conditioning below72° F (23° C) or in colder climates with low soil temperatures.

Sap stain or blue stain fungi may causediscoloration of cut lumber but are notreported to lead to rot or structural damage and probably do not present an air qualityconcern. Sap stain fungi can be mistaken forStachybotrys species due to their darkcoloration, but scientists note that the growthof Stachybotrys species on wood is extremely

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C O M M O N Q U E S T I O N S A B O U T M O L D60

poor and rarely occurs. Stachybotrys species(e.g. S. atra or S. chartarum) typically occur onfiberboard, gypsum board, paper, dust or lint.These molds are associated with constant highlevels of moisture resulting from flooding, un-repaired plumbing leaks or standing water.They are not often found in crawl spaces.

Growth of other fungi on solid wood in drierconditions (19-30% wood moisture content orambient relative humidity above 70%) isgenerally limited to the surface and does notcause structural damage. Composite materialslike engineered wood products consisting ofbits of wood and adhesives can be structurallydegraded by molds because the mold can oftendigest the adhesives. Composite materialsmust be dried and cleaned very quickly toprevent damage.

Should I Test for Mold?

Advanced Energy does not recommend moldtesting unless there is a specific need toidentify samples by species. As detailed below,it is generally expensive and time-consumingto get reliable mold sampling and analysis.Visible mold, regardless of species, indicates amoisture problem that requires attention. Insome cases, molds are located in hidden areasor are simply not visible to the naked eye.Whether visible or not, the key to suppressingmold growth is to remove the mold’s moisture source.

The generally accepted practice for bioaerosolsampling, as laid out by the AmericanConference of Governmental IndustrialHygienists (ACGIH), is to compare indoorsamples with outdoor samples taken at thesame time. If the spore concentrations aresignificantly higher indoors than outdoors orthe species mix is significantly differentindoors than outdoors, it is evidence that moldis growing inside the building.

Unfortunately, interpreting the results ofbioaerosol sampling is fraught with sources ofuncertainty:

• In sample sets taken at a few locations overan interval of hours or days, false positivesand false negatives are common. To reducethe chances that something important hasbeen missed, numerous samples must bemade over extended time periods.

• Bioaerosol sampling requires trainedtechnicians with specialized equipment, andeven then, measurements vary significantlyover short time frames. In controlled airsampling during the field research describedin Section 6, outdoor viable spore countsamples taken within hours of each othervaried by a factor of five.

Ideally, mold samples should be “speciated,”or counted and categorized by individualspecies of mold present in the sample.Speciation provides better evidence fordistinguishing whether there is independentmold growth in a building (or part of the

building) or whether the mold in the buildingsimply reflects the mold present in thesurroundings. “Viable” spore counts are easierto speciate than total spore counts, but viablespore samplers may be biased towards smallerspecies, and growth conditions can varydepending on the lab doing the analysis.

Tape lifts and direct microscopic examinationof surfaces are other techniques to identify thepresence of mold and, to some extent, identifythe mold. These techniques also requiretrained specialists and do not generally allowfor speciation.

Finally, even if sampling is detailed andcomprehensive enough to provide confidencein the measured results, there is no consensuson numerical standards to which test resultscan be compared to indicate a dangerouscondition. Human reaction to mold variesgreatly from individual to individual.

Should I Clean UpExisting Mold in MyCrawl Space?

Mold does not necessarily have to be cleanedup as part of a strategy to improve a crawlspace. Molds go dormant as their environmentdries out. However, dormant mold can stilltrigger allergies, asthma events, or othersymptoms in susceptible individuals. Potentialhealth impacts and the reporting of mold by


C O M M O N Q U E S T I O N S A B O U T M O L D 61

private home inspectors prior to homepurchases is causing more and morehomeowners to consider removing or“remediating” mold from their crawl space. The homeowner’s choice of whether or not toclean up mold depends on their level ofconcern about the potential health impacts ofleaving the mold in place or the impact on thevalue of their home. One specific benefit is thatcleaning out existing mold will make it easierto detect a recurrence in the future.

Of course, there is no point in cleaning upsurface mold without improving the moistureconditions that allowed the mold to grow in thefirst place. The mold would simply grow back.Any activity to clean up surface mold shouldbe part of an overall plan to close the crawlspace permanently.

Mold-contaminated ductwork also presents thequestion of whether to leave the mold in place,clean the ductwork, or replace the ductwork.Flexible duct and fiberglass-lined ductwork isvery difficult, if not impossible, to thoroughlyclean. Other options include leaving the ductas is, replacing the ductwork or sprayingfungicides or encapsulating materials to isolatethe mold in the duct from the air stream. Sheetmetal ductwork is generally more feasible toclean and reuse without encapsulation.

Advanced Energy recommends that you sealductwork and seal holes between the houseand the crawl space whether or not the mold iscleaned up. This air-sealing work reduces thechance that mold, mold byproducts or other

contaminants in the crawl space can enter theliving area of the home by air transport. It isalso critical to help prevent new or cleanedducts from becoming recontaminated. Foradditional protection, the homeowner canupgrade air filtration in the house with stand-alone HEPA units or HEPA air handler/ductsystem filters, and/or apply a fungicide overthe existing mold to provide short-term anti-fungal activity and some level of continuedsuppression.

Advanced Energy has received several reportsof strong ammonia-like odors associated withthe drying-out of existing crawl spaces inNorth Carolina, which may be the result of themold slowly dying or going dormant. The odors persisted for weeks or monthswithout dissipating. Application of a fungicidein conjunction with reducing moisture levelshas been reported to eliminate or prevent this problem.

If a property owner does decide to clean upexisting mold, work can range from spotcleaning of affected areas to comprehensivecleaning of most, if not all surfaces. Large jobsare likely too labor-intensive and timeconsuming to do as a home project. In thesecases, property owners can contract forprofessional cleanup services from waterdamage or mold remediation companies.Building performance or other contractors mayalso offer this service.

This guide is by no means a completereference for doing safe and effective mold

remediation, but simple advice is providedbelow. See the Resources and Referencessection for several published sources of moldcleanup procedures.

During any cleanup, Advanced Energyrecommends the following steps to help reducethe chance of cleaning materials, mold toxins,mold spores, mold fragments, or othercontaminants moving from the crawl space to the living space:

• Turn off any heating and cooling system thatutilizes ductwork in the crawl space.

• Reduce or stop the use of exhaust fans andclothes dryers in the living space.

• Pressurize the living area with HEPA-filteredair and/or depressurize the crawl space.

Additional notes on cleaning mold:

• Remove as much contaminated material aspossible before beginning cleanup.

• Remove contaminated or damagedinsulation. Porous insulation that has beenwetted should be replaced, since it will likelynever recover its designed R-value, evenwhen thoroughly dried.

• Not all fungicides are effective on allmaterials. Follow all manufacturers’recommendations for application and safehandling. Swimming goggles can provideeye protection when working overhead.

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• Chlorine bleach is not a long-termfungicide. If you use chlorine bleach, nevermix it with ammonia because toxic gas canbe produced in fatal levels.

• Liquid cleaning or dry scraping may not remove all staining caused by surface molds.

• HEPA vacuums can be used to collectsurface mold removed by scraping, and arerecommended instead of sweeping to cleanup debris on surfaces or the crawl space floor.

• Pressure washing, sanding or blasting withbaking soda or dry ice are cleaning optionsthat may remove staining. Residual materialsshould be removed afterwards.

• Application of sealants, primers, and painttopcoats may be required to completelycover stains and resist bleed-through.

• Replace the ground vapor retarder after acleanup operation.

• Air-sealing and subfloor repairs are easierwhile insulation is removed.

• Fungicides can be applied after cleaning toencapsulate mold spores that were notremoved and to provide some level ofcontinued mold suppression.

• Monitor and control relative humidity below70% after cleanup to reduce the risk of moldgrowth recurring.

Does Mold Make People Sick?At the time of this writing, the scientific andmedical research communities have notdocumented a causal relationship betweenmold growth in residences and human illness.There is an association between damp homeenvironments and occupant medical conditionslike allergic rhinitis and asthma, however it isunclear whether mold or some other substanceor organism (for example, bacteria) that existsin the same conditions is responsible for the symptoms.

The bottom line is that it is clearly less healthyfor humans to live in homes with moistureproblems, and strategies that eliminate thepotential for such problems are beneficial.

Health effects generally attributed to moldexposure are of four types: allergy, irritation,infection, and toxicity. The most commonhealth effects are allergic reactions and asthmaevents. The symptoms can include runny nose,eye irritation, sinusitis, and difficulty breathing.A tiny fraction of allergy sufferers may developmore serious, chronic lung disease fromchronic exposures. Most molds releasealcohols and sulfur compounds, which canirritate mucous membranes and the trigeminalnerve ending in the back of the throat, whichreacts to pungency and irritation. People aresometimes infected by molds, but generally,people become colonized by molds only iftheir immune system is not functioning well.

Some molds produce toxins calledmycotoxins. Mycotoxins are not produced aspart of the act of living, as are the compoundsfrom respiration and nutrient decomposition.They are produced only occasionally by somemold species. It is thought that molds are mostlikely to produce toxins when in competitionwith other molds or bacteria for habitat. In thiscase, people are collateral damage in chemicalwarfare between microscopic creatures. Thebest-documented cases of mycotoxinpoisoning are from veterinary medicine whenlivestock eat mold-contaminated material.There is not much human data to help usunderstand the risks from mycotoxin exposure,however, the toxins do exist and some of themare similar in toxicity to nerve gases.


R E S O U R C E S A N D R E F E R E N C E S 63

Section 8

RESOURCES AND

REFERENCES

Online Resources

American Conference ofGovernmental Industrial Hygienistswww.acgih.org

American Red Crosswww.redcross.org

“Repairing Your Flooded Home”www.redcross.org/services/disaster/afterdis/reptoc.html

Canada Mortgage and HousingCorporationwww.cmhc-schl.gc.ca/en/index.cfm

Measuring air flow with plastic bags: Searchfor “garbage bag”

Centers for Disease Control andPrevention (CDC)www.cdc.gov

Mold informationwww.cdc.gov/nceh/airpollution/mold

Federal Emergency ManagementAgency (FEMA)www.fema.gov

“Technical Bulletin 1-93, Openings inFoundation Walls”

Florida Solar Energy Center (FSEC)www.fsec.ucf.edu

“Florida Home Mold & Mildew Guide for Consumers”www.fsec.ucf.edu/bldg/science/mold

National Association of HomeBuilders (NAHB) Research Center –ToolBase Services“Mold in Residential Buildings”http://toolbase.org/index-toolbase.asp(search for “mold” if necessary)

U.S. Forest Products Laboratorywww.fpl.fs.fed.us (search for “wood handbook”)

Products and ServicesThe following is a list of the manufacturers or providers of products and services used inAdvanced Energy projects discussed in this guide.

Product/Service Manufacturer/ProviderAnemometer/air flow meter TIFBackflow dampers FamcoCarbon monoxide monitors CO-ExpertsConstant airflow regulators American AldesDuct mastic RCD Corp.Flood vents (FEMA/NFIP-compliant) Smartvent, Inc.Fire-rated foam insulation Dow Chemical (Thermax brand)Fuel gas leak detectors S-TechHigh performance vapor retarder Raven IndustriesLiquid water alarms Basement SystemsMold sample analysis Environmental Microbiology LabOutside air intake and filter housing Indoor Environmental SystemsRadon test kits and analysis AccuStar LabsSump pumps Basement SystemsWireless Temperature/RH meters Oregon ScientificWood moisture meters Wagner, Delmhorst

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U.S. Environmental ProtectionAgencywww.epa.gov

“A Brief Guide to Mold, Moisture and YourHome”www.epa.gov/iaq/molds/moldguide.html

“Mold Remediation in Schools andCommercial Buildings”www.epa.gov/iaq/molds/mold_remediation.html

Indoor air qualitywww.epa.gov/iaq/pubs/index.html#homes

Radon informationwww.epa.gov/radon/

Technical ReferencesACGIH, 1999: “Bioaerosols – Assessment andcontrol.” American Conference of GovernmentalIndustrial Hygienists, Cincinnati, Ohio.

Brennan, Terry and Harriet Burge. 2005.“Assessing Mold in Buildings”. ASHRAEJournal, January 2005. American Society ofHeating, Refrigeration and Air-conditioningEngineers. Atlanta, GA.

Burge. 2004. “Wood Decaying Fungi – AnInsight on Types and Roles in Wood Decay.”The Environmental Reporter Volume 2, Issue 5.Environmental Microbiology Laboratory, Inc.

Davis, Bruce and William E. Warren. 2002.Field Study Pilot Report: A field study

comparison of the energy and moistureperformance characteristics of ventilatedversus sealed crawl spaces in the south.Raleigh, N.C.: Advanced Energy.

Davis, Bruce, William E. Warren and William B.Rose. 2002. Technology Assessment Report: A field study comparison of the energy andmoisture performance characteristics ofventilated versus sealed crawl spaces in thesouth. Raleigh, N.C.: Advanced Energy.

Fallah, Payam and Kamash Ramanathan. 2004.“Fungi of the Month (II): Lumberyard molds –Ceratocystis/Ophiostoma (C/O) group.” TheEnvironmental Reporter Volume 2, Issue 5.Environmental Microbiology Laboratory, Inc.

Hill, William W. 1998. “Measured EnergyPenalties from Crawl Space Ventilation.” InProceedings of the 1998 Summer Study onEnergy Efficiency in Buildings, Vol. 1.Washington, D.C. American Council for anEnergy Efficient Economy.

Rose, W. B. 1994. “A Review of the Regulatoryand Technical Literature Related to CrawlSpace Moisture Control.” In ASHRAETransactions, Vol. 100 Pt. 1. Atlanta, Ga.American Society of Heating, Refrigerating and Air-Conditioning Engineers.

Rose, W. B. and A. TenWolde. 1994. Issues incrawl space design and construction – a

symposium summary. Recommended Practicesfor Controlling Moisture in Crawl Spaces,ASHRAE Technical Data Bulletin volume 10,number 3. American Society of Heating,Refrigerating and Air-Conditioning Engineers,Atlanta, Ga.

Other ResourcesIICRC. 2003. Standard and Reference Guidefor Professional Mold Remediation S520.Institute of Inspection, Cleaning andRestoration Certification, Vancouver, Wash.

Institute of Medicine, 2004. Damp IndoorSpaces and Health. Committee on DampIndoor Spaces and Health; Institute ofMedicine, National Academies Press.

NYCDOH, 2000. Guidelines on Assessmentand Remediation of Fungi in IndoorEnvironments. New York City Department of Health.


A P P E N D I C E S 65

Appendix A

A QUICK OVERVIEWOF DUCT SEALING

Sealing ductwork for forced-air heating and coolingsystems is one of the most effective ways to improveenergy efficiency and indoor air quality in a home. Ifyou have any gas-fired or other fuel-burningappliances in the home, you should contact a buildingperformance professional to assess whether ductsealing will cause a combustion safety problem. It isideal to contact a building performance professional inany case, so that any necessary changes to the ductsystem can be implemented before sealing, and so thatthe duct tightness improvement and combustion safetycan be verified after the sealing work is complete.Sealing ducts involves the following steps:

1. Seal all permanent connections or seams in theduct system with duct mastic

2. Embed fiberglass mesh tape in the mastic atconnections or seams with gaps larger than 1/8 inch.

3. Embed fiberglass mesh tape in the mastic atconnections or seams within ten feet of an airhandler unit.

4. Mechanically fasten the inner liners of flexible ductsto register boots and seal the joint with mastic.Mechanically fasten the outer liner to the registerboot. Zip-tie connectors are typically used for themechanically attachments.

5. Seal duct register boots with mastic to the subfloor,drywall or other paneling they penetrate. Seal jointsor gaps in the boot itself with mastic.

6. Gasket or tape access panels for the air handler orfiltering systems.

7. Seal permanent panels, electrical, refrigerant andcondensate line penetrations, and any unused holesin the air handler permanently.

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Appendix B

SIMPLIFIEDPSYCHROMETRICCHARTThis chart is a simplified version of thecomplex psychrometric charts typically used in the refrigeration and air-conditioningindustries. It is included as a tool forcalculating the dew point temperature of air

when temperature and relative humidity areknown, and for predicting changes to dewpoint temperature or relative humidity when theair temperature changes.

Sensible temperature (also referred to as “drybulb” temperature) is read on the bottom scaleof the chart and is the temperature reading youwould get from a standard thermometer.Relative humidity is plotted on the curved linesin the center of the chart. Dew pointtemperature is read along the curved left sideof the chart.

As a quick example, say that you have airconditions of 85° F and 60% relative humidity.Find 85° F on the sensible temperature scale atthe bottom of the chart, then go up verticallyuntil you reach the intersection with the 60%relative humidity curve, at point A. Todetermine the corresponding dew pointtemperature, go left horizontally until you reachthe dew point temperature scale on the left sideof the chart at point B, which indicates that thedew point temperature is 70° F. To find out therelative humidity of this air at differenttemperatures, go right horizontally until youline up vertically with the desired sensibletemperature. For example, going right to pointC indicates that at 73° F sensible temperature,the relative humidity of this air would be 90%.

20 30 40 50 60 70 80 90 100

2530 35

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A P P E N D I C E S 67

Appendix C

WOOD MOISTURECONTENT ATDIFFERENTTEMPERATURES ANDRELATIVEHUMIDITIES

Taking a single-point measurement of either woodmoisture content or relative humidity in a crawl spacemay not provide a complete picture of the long-termmoisture conditions inside the crawl space. Relativehumidity can vary much more quickly than woodmoisture content, and wood moisture content readingscan be dramatically increased by the presence ofintermittent condensation on the surface of the wood.

The table below relates wood moisture content andambient temperature to long-term conditions of relativehumidity. If you can measure wood moisture content andambient temperature, you can use this table to thenestimate the long-term relative humidity that the woodhas been exposed to. Note that wood moisture contentvaries only slightly (0.5% to 1.2%) at a particularrelative humidity over the range of temperature from 40°F to 90° F.

For example, if you were to measure wood moisturecontent of 18% in a 70° F crawl space, then you canestimate that the wood has been exposed to relativehumidity of approximately 85% over recent days orweeks, even if the relative humidity at the time of yourmeasurement is much lower due to drier outsideconditions.

Note that when the crawl space is vented with outside air,relative humidity inside the crawl space can changesignificantly over short periods of time. In somesituations, measurements of relative humidity and woodmoisture content may still appear to be contradictoryeven when using the equilibrium data from the table. Themore controlled conditions in a closed crawl spacegenerally make it easier to interpret measurements.

Moisture content of wood in equilibrium with stated temperature and relative humidity(Source: U.S. Forest Products Laboratory, Wood Handbook, Table 3-4.)

Temperature Moisture content (%) at various relative humidity values

°C °F 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95%

4.4 40 7.9 8.7 9.5 10.4 11.3 12.3 13.5 14.9 16.5 18.5 21 24.3

10 50 7.9 8.7 9.5 10.3 11.2 12.3 13.4 14.8 16.4 18.4 20.9 24.3

15.6 60 7.8 8.6 9.4 10.2 11.1 12.1 13.3 14.6 16.2 18.2 20.7 24.1

21.1 70 7.7 8.5 9.2 10.1 11 12 13.1 14.4 16 17.9 20.5 23.9

26.7 80 7.6 8.3 9.1 9.9 10.8 11.7 12.9 14.2 15.7 17.7 20.2 23.6

32.2 90 7.4 8.1 8.9 9.7 10.5 11.5 12.6 13.9 15.4 17.3 19.8 23.3

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ACCA – Air Conditioning Contractors of America

ACGIH – American Conference of Governmental Industrial Hygienists

AE – Advanced Energy

ARI – Air Conditioning and Refrigeration Institute

ASHRAE – American Society of Heating, Refrigerating and Air-Conditioning Engineers

ASTM – American Society for Testing and Materials

BTU – British thermal unit

CAR – constant airflow regulator

CDC – Centers for Disease Control and Prevention

CMU – concrete masonry unit

CO – carbon monoxide

DOE – U.S. Department of Energy

EPA – U.S. Environmental Protection Agency

EPDM – Ethylene propylene diene terpolymer

FEMA – Federal Emergency Management Agency

FHA – Federal Housing Administration

FSEC – Florida Solar Energy Center

HEPA – High-Efficiency Particulate Arrestance

HSPF – Heating System Performance Factor

HVAC – Heating, Ventilation and Air Conditioning

ICC NER – International Code Council National Evaluation Report

IECC – International Energy Conservation Code

IRC – International Residential Code

MADD – Mold Amplification and Delivery Device

NAHB – National Association of Home Builders

NBS – National Bureau of Standards

NFIP – National Flood Insurance Program

ORNL – Oak Ridge National Laboratory

OSHA – Occupational Safety and Health Administration

SEER – Seasonal Energy Efficiency Ratio

SFHA – Special Flood Hazard Area

TIF – Thermal Industries of Florida, Inc.

Appendix D

GLOSSARY OF ACRONYMS AND ABBREVIATIONS


I N D E X 69

Index

abbreviations, 68absolute moisture, 52–54. See also dew pointaccess doors or panels: to basements or other structures,

40; building codes, 41; closing during construction,37; in converted crawl spaces, 38; in crawl spacedesigns, 28–35; to ductwork, 65; inspectingannually, 22, 48; protecting from runoff, 8

acronyms, 68Advanced Energy: future research, 3; Princeville project,

1, 49–57; sealed vapor retarders recommendations,12; symbols in recommendations, 7

air: air supply (See air supply); combustion air (Seecombustion air supply); house air, 41; humid air,preventing, 9–10; mold spore content, 49, 56–57,59, 60; properties of, 4; psychrometric charts, 66;temperature, 51–52, 66

Air Conditioning Contractors of America, 4air conditioning systems, 25–26, 28–31, 46, 55air filtration, 61, 63air flow, 42air flow meters, 25, 63air flow regulators, 25, 26, 63air intake housings, 63air leakage, 10, 49air pressure, 26, 42, 50, 61air-sealed walls, 2air supply: air intake housings, 63; in building codes, 39,

41; combustion air (See combustion air supply);house air, 41; humidity control in crawl spaces, 13,25–26, 28–31; in research houses, 51

alarms. See monitors and alarmsallergies, 60, 62ambient temperature, 67American Conference of Governmental Industrial

Hygienists (ACGIH), 60

American Society for Testing and Materials (ASTM), 42, 51American Society of Heating, Refrigerating and Air-

Conditioning Engineers (ASHRAE), 49ammonia, 62ammonia-like odors, 47, 61Anderson samples, 56anemometers, 25, 63appliances: atmospheric draft appliances, 15, 47;

backdrafts, 43, 47; combustion air supply, 42, 47; incrawl space specifications, 28–35; direct-vent fuel-burning appliances, 15, 43, 47; discharge pipingand drains, 13; drafts for, 15; gas- or oil-fired, 15,42, 43, 47; natural draft appliances, 15, 47; sealingducts, 65

asbestos, 43, 47ASHRAE Recommended Practices for Controlling

Moisture in Crawl Spaces, 49asthma, 60, 62ASTM E 84 standard, 51ASTM E 152 standard, 42atmospheric draft appliances, 15, 47

backdraft dampers, 25, 42backdrafts, 43, 47backflow dampers, 25, 63backflow valves, 12, 36baking soda treatments, 62balancing dampers, 25, 51band joists, 9, 14, 16, 42, 51basements, 40bathroom vents, 13, 28–35, 37, 46batt insulation, 14, 16, 47, 51batteries, 22, 48bibliography, 63–64Bill Warren Energy Services, 49bioaerosol sampling, 49, 60bleach, 62blocking sources of moisture, 8–12

blown insulation, 16blue stain fungi, 59–60blue water drop symbol, 36boilers, 15, 47Brennan, Terry, 49builders, 2, 40building codes, 19, 39–42building scientists, 40Burkard samplers, 56butterfly dampers, 25, 51

cabinetry, 45callbacks, 23capillary action. See wickingcapillary breaks in specifications, 28–35carbon monoxide, 15, 47, 63central air conditioning, 25, 26. See also air conditioning

systemscertificates of occupancy, 20, 38check valves, 12chemical storage, 47chlorine bleach, 62cleaning mold, 47, 60–62climate, 4–5, 57closed crawl space installers, 2, 19, 40closed crawl spaces: building code changes, 39–43,

41–42; code officials and, 20; combustion safety,15; components of, 2, 7; construction sequence,36–38; contracts and pricing for, 23; convertingwall-vented spaces to, 45–48; defined, 1; designsfor, 2, 19–20, 25, 28–35; fire safety, 16 42; humiditycontrol, 25–27; installing, 2, 19, 40; insulation (Seeinsulation); job-site logistics, 20–22; maintenance,22, 48; moisture management, 7–13; pest control,13–14; Princeville research project, 49–57; qualityassurance, 22–23; radon safety, 17, 43, 56, 63;unregulated specifications, 42-43; training labor, 20

"closed with a sealed liner" crawl spaces, 1

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closed-cell foam insulation, 16clothes dryer exhaust vents, 13, 28–35, 37, 40, 46, 61code officials, 2, 20, 39–40combustion air supply, 15, 42, 43, 45, 47, 65. See also

air supplycomfort levels, 55-56complex home designs, 3, 21, 36composite materials, 60condensate drain pans, 13, 28–35, 37, 40, 46condensation: in crawl spaces, 2, 4, 46, 50;

dehumidifiers and, 27, 32–35; in Princevilleresearch studies, 53; water vapor and, 4

conditioned air: in building codes, 39, 41; humiditycontrol in crawl spaces, 13, 25–26, 28–31; inresearch houses, 51. See also air conditioningsystems

conditioned crawl spaces, 1conditioned spaces, 41–42constant airflow regulators, 25, 26, 63construction process, 21–22, 36–38contractor damage to vapor retarders, 22, 48contracts for crawl space installation, 23conventional wisdom, crawl spaces and, 20conversions to closed crawl spaces, 21, 45–48, 50–51cooling equipment. See HVAC equipmentcoordinating schedules, 20–21cosmetic problems from dampness, 45, 53costs of closed crawl spaces, 20, 23crawl spaces, 1; building code changes, 39–43;

conventional wisdom and, 20; ductwork schematics,26; fire hazards in, 16; maintenance, 22, 48;Princeville research project, 49–57; problems in, 2;raising above grade, 8; web site information, 1. Seealso closed crawl spaces; wall-vented crawl spaces

customizing crawl space design, 19–20

damp-proofing foundations, 8, 28–35, 40darkness, mold growth and, 59Dastur, Cyrus, 49data collection in research, 51–52Davis, Bruce, 49debris, 40, 46–47decks, 9dehumidifiers: advantages and disadvantages, 27; in

building code, 41; crawl space designs for, 32–35;inspecting, 22; installing, 13; temporaryconstruction installation, 21, 37

depressurization systems, 17designs for closed crawl spaces, 19–20, 25, 28–35detectors. See monitors and alarmsdew point, 4–5, 52–54, 55, 66direct-vent appliances, 15, 28–35, 43, 47doors. See access doors or panelsdormant mold, 60–61drafts for combustion appliances, 15, 47drains and drainage: for appliances, 13; in closed crawl

spaces, 2, 12, 13, 28–35, 36, 40; foundation drains,8, 28–35; inspecting, 22; sizing, 42; sub-surfacedrain pipes, 8; for surface water, 8; in wall-ventedspaces, 45

drawings for crawl spaces, 25, 28–35dried-in phase of construction, 22, 37dry air, 25–26dry bulb temperature, 66dry ice treatments, 62dry rot, 59dryer vents. See clothes dryer exhaust ventsdrying out crawl spaces, 4, 45, 47, 51, 53, 61drying systems, 13drywall, 45, 53duct mastic. See masticductwork: conditioned air from, 13, 25–26, 28–31;

leakage in, 50; mold-contaminated, 61; reducing

leakage, 50; schematics, 26, 65; sealing, 9, 28–35,40, 46, 65; testing, 49

dust, mold counts and, 57

electrical outlets, 32–35, 37electricity submeters, 51elevation certificates, 10energy savings, 1, 20, 51, 54–55, 57, 65envelope leakage, 50Environmental Protection Agency (EPA), 17evaporation, 10–12, 48exhaust fans, 41, 43, 61exterior water management: in closed crawl spaces, 2;

roof runoff, 8, 28–35, 37, 40; site grading, 8, 20,40, 45; surface water, 8

faced batt insulation, 14Factory Mutual 4880 standard, 42, 51false positive or negative tests, 60fans, 41, 43, 61Federal Emergency Management Agency (FEMA), 9, 10Federal Housing Administration, 39fiberglass insulation, 16, 40fiberglass mesh tape, 11, 38, 51, 65field studies. See Princeville research projectfiltering air, 61, 63fire hazards, 16fire ratings, 14, 16, 42, 63fireblocking, 16flashing, 8float-kill switches, 13flood vents, 9, 10, 28–35, 40, 63flooding, 9, 10floor insulation, 2, 28–29, 32–33, 54, 57floor joists, 28–35floor platform phase in construction, 37flow hoods, 25


I N D E X 71

flow rates, specifying, 42FM 4880 standard, 42, 51foam insulation, 14, 16, 42, 51, 63forced-air heating, 65foundations: crawl space design and, 2; damp-proofing,

8; drain systems, 8, 28–35, 40, 45; hollow block,10; moisture management in construction, 36–37;repair/waterproofing contractors, 19; schedulingconstruction, 20; sealing gaps, 9; waterproofing, 8,28–35, 45

freezing pipes, 54fuel-burning appliances, 15, 28–35, 42, 43, 47, 65fuel-gas leak detectors/alarms, 15, 63fungi, 59, 60fungicides, 47, 61, 62furnaces, 15, 28–35, 42

garages, 40gases in soil, 12gas-fired appliances, 15, 28–35, 42, 43, 47, 65gaskets, 9, 37, 65gasoline, 16, 22, 47, 48general contractors, 19GFCI-protected outlets, 32–35, 37grading: costs and, 23; in crawl spaces, 12, 28–35, 36,

40; pitch of, 42; site grading, 8, 28–35, 36, 40, 45gravel beds, 8ground: evaporation from, 10–12; gases in soil, 12ground vapor retarders: in building codes, 39, 41; in

existing crawl spaces, 50; installing duringconstruction, 37–38; mold cleanup and, 62;preventing evaporation, 10; in research houses, 50,51; securing, 12, 42; in wall-vented crawl spaces,46, 52

groundwater, 8guarantees (warrantees), 14, 20, 21, 22, 23, 38, 47gutters, 8, 21, 40

hardwood floors, 45, 53hazardous materials, 22, 47, 48health impacts of mold, 60-61, 62heat pumps, 50heating equipment. See HVAC equipmentheating-based climates, 57HEPA filters (High-Efficiency Particulate Arrestance), 20,

61hidden areas, pest inspections and, 13–14High Radon Potential counties, 17High-Efficiency Particulate Arrestance (HEPA) filters, 20,

61high-performance vapor retarders, 63hollow block foundations, 10home inspectors, 3home performance contractors, 19house air, 41house exhaust fans, 43house leakage, 50humidity, 9–10, 25–27, 55. See also relative humidityHVAC contractors, 19HVAC equipment: activating, 38; average use, 54–55;

closed crawl spaces and downsizing, 12, 25;heating- or cooling-based climates, 57; in researchhouses, 50; sealing, 65

hygrothermal modeling, 57

ignition barriers, 16, 42improving wall-vented crawl spaces, 45–48, 50–51induced-draft combustion systems, 47infection, from mold, 62initial costs, 23insect pests. See pest managementinspection: closed crawl spaces, 22, 48; dehumidifiers,

27; hidden or obstructed areas, 13–14; by pestmanagement professionals (See pest management);post-occupancy, 38; wall-vent conversion projects, 46

inspection gaps, 28–35, 39, 51instrumentation in research project, 51–52insulation: attachments, 42; on band joists, 14; in

building codes, 39, 42; climate and, 57; in closedcrawl spaces, 16; in conditioned crawl spaces, 1;fire ratings and safety, 16, 42; on flood vents, 10;floor insulation, 28–29, 32–33, 54, 57; installingduring construction, 37; L-shaped method, 39;moisture in, 2; mold cleanup and, 61; pestinspection and, 14; in Princeville research project,54; replacing, 47; in research houses, 51; sampleinstallations, 28–35; scheduling construction, 21;wall insulation, 30–31, 34–35, 42, 54, 57; in wall-vented crawl spaces, 41

insulation contractors, 19International Code Council National Evaluation Report

(ICC NER), 16International Energy Conservation Code, 20, 39International Residential Code (IRC), 16, 17, 39interviews with property owners, 49irrigation systems, 8, 21, 45irritation, from mold, 62isolating crawl spaces, 46

job-site logistics, 20–22joints, 9, 11

Karagiozis, Achilles, 49kitchen vents, 13, 28–35, 37, 46

L-shaped method of insulating, 39labor, training, 20landscaping, 8, 21lapping seams, 11leakage, 45, 49, 50liquid water: alarms, 13, 22, 47, 63; mold growth and,

59; removing, 12–13; standing water, 48

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local code officials, 20logistics of crawl space jobs, 20–22long construction schedules, 21, 36low indoor temperatures, 46low-volume construction, 3, 36Lstiburek, Joe, 49

main construction phase, 37maintenance: closed crawl spaces, 22, 38, 48;

dehumidifiers, 27; reductions in, 23make-up air, 43manufacturers, 63masonry, 16, 20mastic: in building codes, 40; in construction phase, 38;

in crawl space specifications, 28–35; manufacturers,63; in research houses, 51; sealing ductwork, 65;sealing vapor retarders, 11

measuring crawl spaces, 49mechanical attachment of vapor retarders, 10, 11, 42, 51mechanical contractors, 19, 21mechanical drying systems, 2, 13Model Energy Code, 20moisture levels: comfort and, 55-56; mold growth and,

59; passive ventilation and, 4; in Princevilleresearch project, 1, 52–54; in wall-vented crawlspaces, 45

moisture management: blocking sources of moisture, 2,8–12; in building codes, 41–42; in closed crawlspaces, 7–13; compromising, 17; duringconstruction, 21–22, 36–38; overview, 7; removingmoisture, 12–13

mold: cleaning up, 47, 60–62; in crawl spaces, 4, 20, 50;debris and, 46–47; dormancy, 60–61; exhaust airand, 43; growth of, 2, 59; health impacts, 60-61, 62;odors and, 47; photographs, 5; in Princevilleresearch studies, 54, 56–57; speciating, 60; sporecounts, 49, 56–57, 59, 60; stirring up settled dust,

57; tests, 21, 60; types of, 59–60; warrantiesagainst, 23

mold sample analysis, 63monitors and alarms: after mold cleanup, 62; annual

monitoring services, 22; for carbon monoxide, 15;for humidity and moisture, 13, 22, 46, 47; installingduring construction, 22; manufacturers, 63; inPrinceville research project, 51–52; for radon, 56;for temperature, 47

movement of vapor retarders, 11, 12mycotoxins, 62

National Bureau of Standards, 39National Flood Insurance Program, 10natural draft appliances, 15, 47natural gas alarms, 15negative air pressures, 26non-porous insulation, 16North Carolina, climate of, 4–5North Carolina Building Code Council, 40North Carolina Department of Insurance, 40North Carolina Mechanical Code, 15North Carolina Residential Code, 1–2, 7, 16, 39–43,

50–51North Carolina Solar Center, 49

Oak Ridge National Laboratory, 57obstructed areas, inspections and, 13–14occupant requirements, 20, 54–55odors, 47, 61oil-fired appliances, 15, 28–35, 42, 43, 47, 65organic material, 40outside air, 4, 26outside sources of moisture, 8–12

p-traps, 12packaged unit equipment, 9

paint topcoats, 62passive ventilation, 2, 4penetrations: fire safety and, 16; in sample designs,

28–35; sealing, 9, 36, 40, 46; water-tightness and,36

perimeter walls: costs of crawl spaces and, 23;evaporation from, 10–12; insulation, 16, 39, 51;pest inspection and, 14

pest management: building codes and, 40; closed crawlspaces and, 13–14; crawl space designs and, 13;inspection gaps, 28–35, 39, 51; liabilities andhidden areas, 13–14; professionals, 19, 20, 40, 47;scheduling, 21; warranties, 20, 47

Piedmont region, North Carolina, 49–50piers, 23, 37pipes: appliance discharge, 13; freezing, 54; sub-surface

drains, 8; temperature/pressure relief, 28–35, 37, 40pitch of grade, 42plumbing leaks, 45polyethylene vapor retarders, 10, 40. See also vapor

retarderspolyisocyanurate foam, 51pony walls, 16porches, 9, 40porous insulation, 47post-occupancy maintenance. See maintenancepressure effects: mold cleanup and, 61; negative

pressures, 26; testing, 50pressure relief pipes, 28–35, 37, 40pressure relief vents, 42pressure washing, 62pre-treatment for pests, 14, 21pricing installation of crawl spaces, 23primers, 62Princeville research project, 1; dew point conditions, 5;

energy performance, 54–55; field study experimentsetup, 50–51; implications of, 57; instrumentation


I N D E X 73

and data collection, 51–52; moisture performance,52–54; mold sampling, 56–57; photographs, 3;quantifying existing crawl spaces, 49–50; radonmeasurements, 56; temperature conditions, 5, 54

private home inspectors, 3product manufacturers, 40, 63professional engineers, 19propane alarms, 15property owners, 3, 19, 38, 48, 49protecting vapor retarders, 11, 38, 41psychrometric charts, 4, 5, 66pumps: for appliance drainage, 13; in closed crawl

spaces, 2; for dehumidifier condensate, 27; sumppumps (See sump pumps)

quality assurance, 22–23

radon safety, 17, 43, 56radon test kits, 63rain, 4, 21, 45, 50Recommended Practices for Controlling Moisture in

Crawl Spaces, 49references and resources, 63–64relative humidity: in closed crawl spaces, 1, 52–54; mold

growth and, 59; monitors, 13, 47, 63; psychrometriccharts, 66; spring and fall seasons, 26;understanding, 4–5; in wall-vented crawl spaces, 2,52–54; wood moisture levels, 67

removing moisture, 12–13repair kits, 22repairing structural damage, 46replacing insulation, 47research implications of Princeville project, 1, 49–57resources and references, 63–64respiratory hazards, 20, 57, 62retrofits. See conversionsreturn air ducts, 41

return plenums, 42reverse flow, 12rigid foam insulation, 14rock wool insulation, 16, 40roof runoff, 8, 28–35, 37, 40Rose, William, 39, 49rot, 2, 5, 46, 59runoff systems, 8, 28–35, 37, 40

safety considerations: combustion safety, 15; fire safety,16, 42; radon safety, 17, 43, 56, 63; symbols inrecommendations, 7

sanding, 62sap stain fungi, 59–60scheduling projects, 20–22, 36sealants, 9, 37, 62sealed crawl spaces, 1sealing: details in specifications, 28–35; ductwork, 65;

gaps in foundations, 9; vapor retarders, 11, 12seams, 11, 38seasonal climate changes, 26, 27, 53, 54–55sensible temperature, 66SFHA (Special Flood Hazard Area), 9, 10signs, 22, 38sill plates, 9, 14, 28–35, 37site conditions, 19–20site grading, 8, 20, 40, 45sizing: drains, 42; HVAC equipment, 12, 25software, 20, 57solvents, 16, 22, 48sources of moisture, blocking, 8–12, 45–46southeastern United States climate, 2Southface North Carolina, 49Special Flood Hazard Area (SFHA), 9, 10spore counts, 49, 56–57, 60spores, 59spot cleaning mold, 61

sprinkler systems, 8, 45Stachybotrys species, 59-60stack effect, 43stains, mold, 62stamped letters of approval, 20, 40standards for closed crawl spaces, 19standby air leakage, 10standing water. See liquid waterStraube, John, 49structural damage, 46subfloors, 9, 16, 21–22, 37, 62sub-membrane depressurization systems, 17sub-slab depressurization systems, 17sub-surface drain pipes, 8summer temperatures, 4–5sump pumps: activating, 38; adding to wall-vented

spaces, 45; in closed crawl spaces, 12, 40; in crawlspace specifications, 28–35; discharge drainage, 13;inspecting, 22; manufacturers, 63; pits for, 37;ratings, 42; in retrofits, 47

supply air. See air supply; combustion air supplysupply plenums, 42surface mold, 61surface water, 8symbols in recommendations, 7, 36symptoms of mold-related illnesses, 60-61, 62

tape joints, 11tears in vapor retarders, 11temperature: air temperature, 4–5, 51–52; dew point (See

dew point); low indoor temperature, 46; monitors,47, 63; in Princeville research project, 54; sensibletemperature, 66; wood moisture levels and, 67

temperature/pressure relief pipes, 28–35, 37, 40temporary vapor retarders, 37tension wires, 47TenWolde, Anton, 49

Clos

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I N D E X74

termites: crawl space designs, 13; dry wood and, 54;inspection gaps, 14, 28–35, 51

testing: crawl space designs, 3; mold, 60; vaporretarders, 12

thermal barriers, 16, 42thermal insulation, 16, 42thermal performance, 50thermostat settings, 54, 55-56Thomann, Wayne, 49tiger teeth, 47toxicity of mold, 62training needs, 20two-pipe fuel-burning appliances, 15, 28–35, 43, 47

Underwriters Laboratories UL 1040 standard, 42Underwriters Laboratories UL 1715 standard, 42unvented crawl spaces, 1, 39U.S. Department of Energy, 49

vacuums, 62vapor retarders: in building codes, 40, 41; in closed

crawl spaces, 2; ground and wall, 10–12;inspecting, 22, 48; manufacturers, 63; pestinspection and, 14; protecting, 11; repair kits, 22;sealing, 12, 28–35; temporary constructioninstallation, 37

vent dams, 41ventilation fans, 5ventilation openings, 41vents, 42, 45. See also flood vents; wall-vented crawl

spacesviable spore counts, 60visible mold, 60volunteer-built homes, 21

wall evaporation, 10–12wall insulation: attachments, 42; climate and, 57; in

crawl space specifications, 30–31, 34–35; installingduring construction, 37; in Princeville researchproject, 54

wall vapor retarders, 10, 11, 36, 37, 42wall-vented crawl spaces: in building codes, 40, 41;

converting to closed, 45–48; isolating from house,46; mold in, 56, 59; passive ventilation and, 4;Princeville research project, 1, 49–57; problemswith moisture, 2; quantifying for research, 49–50;relative humidity in, 2

warranties, 14, 20, 21, 22, 23, 38, 47Warren, Bill, 49water. See liquid water; water vaporwater alarms, 22water drop symbol in specifications, 36water heaters, 15, 28–35, 37, 42, 47water vapor, 4, 12–13waterproofing foundations, 8, 28–35, 45weather strips, 10web sites: resources, 63–64; www.crawlspaces.org, 1, 40wet bulb temperature, 66wicking, 8, 12, 14, 30–31wireless meters, 63wood: cabinetry, 45; perimeter walls, 16; rot in crawl

space framing, 2, 4, 5, 46, 59; trim carpentry, 45, 53wood moisture levels, 2, 4, 51, 52–54, 67wood moisture meters, 63

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