attic-crawlspace ventilation - iw 2015 · 10/26/2016 1 property services, inc. attic &...

10/26/2016

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Property Services, Inc.

Attic & Crawlspace Ventilation


Joe Konopacki

• Multifamily Property Management & Rehab

• Home InspectionsIL Licensed Home Inspector

• Building ScienceBPI Building Analyst RESNet Energy RaterBPI Trainer


What results from poor ventilation?



Overview

Why ventilate?

Symptom, Source, Solution

How to ventilate (in most cases).

Purpose of space, Driving force, Openings, Distribution

Ventilating crawlspaces.

Special cases.

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Purpose of Attic Ventilation

Manage Heat

Manage Moisture

Image credit Michael Meininger

www.mmeininger.com



Heat Management

• Material Failure

• Discomfort

• Ice-Dam Damage

• Poor Efficiency

- Keep the entire roof

as cool as possible, in

summer and winter.-



Heat Management



Heat Management

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Heat Management



Heat Management



• Convection

Heat Management

• Conduction

• Radiation



Convection vs. Radiation

(ventilation)

Heat Management

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Heat Management

William Rose PhD

University of Illinois

Shingle Research Lab



Heat Management

William Rose PhD





Heat Management

Important Factors

129 132

196

204

White

Vented

White

Unvented

Black

Vented

Black

Unvented

Max Temperatures

Rudd, A., 1996. “Vented and Sealed Attics in Hot Climates”

Carl G. Cash, PE, and Edward G. Lyon, PE, 2002.

“What's the value of ventilation?”

1. Geography

2. Orientation

3. Roof Color

4. VentilationHigh Solar

Reflectance

High Solar

Absorption



Heat Management

William Rose PhD



Expected Shingle Life

• Cheap, Dark shingles - shorter service life

• High quality, Light shingles - longer service life

• Organic shingles (1980’s) - end of service life

• Vented vs Unvented - not a factor

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Heat Management

Icicles & Ice Dams



Heat Management

Icicles & Ice Dams



Heat Management

Icicles & Ice Dams

Heat Loss

• Missing/thin insulation

• Air leaks from home

• Heat source (furnace)

• “Vagrant heat loss”



Heat Management

Icicles & Ice Dams

Vagrant Heat Loss

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Heat Management

Icicles & Ice Dams

No Heat Loss

• No melting

• No problems

• Except maybe

large snow load



Heat Management

• Ventilate

• Air seal

• Insulate

Before

After



• Convection

Heat Management

• Conduction

• Radiation

• Maintain air flow

• Cool the sheathing

• Shading

• Reflective Roof Covering

• Interior radiant barriers

• (Air Seal first)

• Insulation



Moisture Management

Condensation / Drips

Mildew / Mold

Rot

-like substance

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Moisture Management

Moisture comes up from the home.

Seal all air leaks from the home!



Moisture Management

JK1



Moisture Management

JK1



Moisture Management

JK1

JK1 Joe Konopacki, 10/5/2014

Slide 28


Slide 29


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Moisture Management

JK1



Moisture Management

JK1



Moisture Management



Moisture Management

• Condensing surfaces

Hot Attic Cold Attic

Condensation on outside of duct Condensation on inside of duct


Slide 31


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Moisture Management

• Permeability of Assembly Layers

Shingles have the

lowest permeance



Moisture Management

Exhaust spot

ventilation to

outside

Halt escaping air-borne

moisture

• Seal Duct

Leaks

• Air

Seal

Even Ventilation Distribution

• Keep air moving

• Limit dead air

spots

Intake

low

Exhaust High

Intake

low



– Passive Gable/End Vents

• Possible in attics

– Needs cross-wind

• Not so in crawlspaces

– Mostly upward vapor diffusion

– Adds to building leakage

– Needs cross-wind

Ventilation Types



Ventilation Types– Active Exhaust (Fan$)

• Is It Necessary ?

– Attics - Not typically

– Hip Roofs - Maybe

– Crawlspaces - w/Humidistat

• Sizing & Position

– Volume – Rate of Exchange (cfm)

– Attic – exhaust to hot side

– Crawlspace – exhaust to cool/damp side

• Interactions to Monitor

– Combustion Safety

– Energy loss

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Position of vents

– Gable vents

– Powered Exhaust fans



Position of vents

– Exhaust

• Roof vents

• Ridge-vents

– Intake

• Continuous or…

• Individual openings

• Away from the home



Position of vents

Vent Chutes

Up & Over Insulation

Every Rafter Cavity

Wind BafflesSoffit

Vent


Attic Ventilation

Chutes & Baffles

• Minimum 1” air space below sheathing.

• Extend beyond installed insulation.

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Continuous

Roof Ventilation



How much Ventilation?

– Total Capacity

• 1/300 ratio for attic with vapor barrier to cond. space

• 1/150 w/o vapor barrier

– Ex: 1500 sqft attic ÷ 300 = 5 sqft

720 sqin• 5 sqft =

• Correct for NFVA



How much ventilation?

– Typical Distribution

• Typical 50% Intake, 50% Exhaust

• 25% along each eave x2

– Ex: 2.5sqft (360sqin) Exhaust

• 1.25sqft(180sqin)

Intake x2 (per Eave)



How much ventilation?

– Recommended Distribution

• 60% Intake 40% Exhaust

• Creates a slightly pressurized attic

– Attic pressure pushes back

against stack effect.

“It's nearly impossible to have

too much [intake ventilation].”

- Paul Scelsi, 2003.

“Balancing Ventilation”

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Attic Size (ft2) Eave 1 (in2

) Eave 2 (in2) Ridge (in

2)

1500 180 180 360

Total Net Free Area (in2) 25% 25% 50%

720

Attic Size (ft2) Eave 1 (in2

) Eave 2 (in2) Ridge (in

2)

1500 216 216 288

Total Net Free Area (in2) 30% 30% 40%

720

Typical

Recommended



Net Free Vent Area

Actual open space available for air flow

per sq-ft of area

Soffit Vent

Edge Vent

Ridge Vent Roof Vent

Gable Vent



Net Free Vent Area

Consider eave depth and vented panel frequency


Attic Ventilation

How much Ventilation?

– 1500 sqft attic

Suppose 30’ x 50’ with 50 linear ft of eave on each side

Choose material with enough Net Free Vent Area

Overhang Depth Matters

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Attic Ventilation

Net Free Vent Area

Consider eave depth and vented panel frequency

3” 5” 9”6” Overhang

144’ 87’ 48’

12” Overhang72’ 44’ 24’

24” Overhang36’ 22’ 12’

Linear ft of vented material needed



Net Free Vent Area

The NRCA Roofing and Waterproofing Manual, Fifth Edition



Unvented Attic

• Hot roofs

– Unvented assembly

• Vented roof deck

– Air space below

deck & shingles


When Unvented Attics makes Sense

• Finished attic space

• Wildfire regions

• Windy rainy/hurricane regions

• Windy winter regions

– Vented roof deck in High Snow-Load Area

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Knee-wall/Cathedraled Attic Variations



Typical Compact/Flat Attic

The Good

, no ventilation and warm roof




The Bad

, some ventilation and warm roof




Moisture is Trapped

In Lower Cavities

The Ugly

, poor ventilation and a colder roof

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Climate Strategies

• Heating Climate

– Keep moisture inside the home

– Insulate to create warm surfaces

– Allow for drying to the outside

– Ventilate cold surfaces

• Cooling Climate

– Keep moisture outside

– Allow for drying to the inside



Purpose of Crawlspace Ventilation

– Manage Moisture

• Reality does not match intent

– Problems

• Only works when air outside is drier – Not so, in warm/humid climates

• Needs cross-wind

• Moisture moves up to drier home (Vapor diffusion)

• Increases building leakage

• Major source of attic moisture!



Crawlspace Ventilation

Vapor Diffusion Building Leakage

Needs

Drier AirNeeds

Cross-Wind

Moisture Allowed to Enter

What if this flooring is vapor tight?




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Encapsulated

or

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Ideal Crawlspace Moisture Control

• Control moisture at the soil… and the walls• Vapor Barrier – 6+mil Poly sheathing

• Sub-slab Ventilation – (radon system)

• Unvented assembly, so seal existing wall vents

• Options:

– Add HVAC supply air into the crawl space -needs transfer grille to home

– Exhaust moist air from the crawl space to outside -needs transfer grille to home

– Install a dehumidifier -no transfer grille



Ideal Crawlspace Moisture Control

• Control moisture at the soil… and the walls

• Options:

– Add HVAC supply air to crawl space

– Exhaust crawl space to outside

• Both require 1cfm/50sqft

– Install a dehumidifier -no transfer grille




Bringing it full circle




Bringing it full circle

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Questions?

attic-crawlspace ventilation - iw 2015 · 10/26/2016 1 property services, inc. attic &...

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