north carolina crawl spaces – vented and closed
DESCRIPTION
North Carolina Crawl Spaces – Vented and Closed. ACI Home Performance 2008 Melissa Malkin-Weber. Presentation Overview. How does the wall vented crawl work? Study Findings Moisture conditions and mold Air pathways Driving forces Transmission of mold to living space - PowerPoint PPT PresentationTRANSCRIPT
North Carolina Crawl Spaces – Vented and Closed
ACI Home Performance 2008
Melissa Malkin-Weber
Presentation Overview
How does the wall vented crawl work?
Study Findings >Moisture conditions and mold >Air pathways>Driving forces>Transmission of mold to living space
N.C. Closed Crawl Space Demonstration studies Study of closed crawls in 2 other climates
Ducts: 55-65 F
H2O pipes: 55-65 F
Floor:65-70 F
Framing:70-78 F
85 F60% RH70 F DP
73 F90% RH70 F DP
The Myth of Vented Drying
Crawl Space Characterization Study Objectives
What conditions in vented crawl spaces Southeast U.S.? Moisture / mold → poor home IAQ? Are vented crawl spaces delivering mold into house?
Study Population
45 housesBetween 2 - 60 years oldAverage age 27 years
Detailed Characterization Protocol
Observational Wood moisture Fungal sampling Building Pressure Diagnostics Measure fungal transmission to the living space
Crawl Space Observational Results
Moisture Data – Mold Conditions
Puddles in on top of vapor retarders– 42% Visible moisture discolorations in crawl space —
49% Evidence of wetting and drying cycle Visible mold — 62% of homes
Moisture Data – Wood Rot Conditions
Visible wood rot — 47% of homes Wood moisture content >25% seen in over 1/3 of homes
(supports wood rot) Wood moisture content >19% seen in another 36% of
homes (mold supporting)
Visible Mold Examples
Mold Sampling Results In Crawl Spaces
~ 6 times the concentration of colony forming units in the crawl space than outdoors
Vented crawl spaces are wet enough to support mold growth, and stay wet long enough for mold to establish
Average Spore Counts Higher in Crawl than Outdoors
# of Houses Outside (CFU/m3)
Crawl space (CFU/m3)
45 3,027 19,102
21 3,235 30,163
14 3,427 16,041
10 2,033 161
Is there a connection between crawl space and living space?
A = outside to houseB = outside to crawl spaceC and D = ducts to crawl spaceE = crawl space to houseG and F = outside to ducts
A
E
DCB
house
crawl space
G return supply
F
Pressure tap setup measured pressures:
Is there a connection between crawl space and living space?
A = outside to houseB = outside to crawl spaceC and D = ducts to crawl spaceE = crawl space to houseG and F = outside to ducts
A
E
DCB
House
Crawl Space
G return supply
F
Pressure tap setup measured pressures:
APT: Pressure tap setup measured pressures
A
E
DCB
house
crawl space
G return supply
F
Measured Duct Leakage and Classification
CFM 25 per ft2 of conditioned floor area *
M3/h/m2 at 25 Pascals of conditioned floor area *
Classification Percent of houses tested
<3% <0.55% Minimal 0
3.1-5% 0.56-0.91% Limited 4
5.1-8% 0.92-1.46% Moderate 9
8.1-12% 1.47-2.19% Excessive 18
>12% >2.20% Major 65
* Cubic Feet per minute at 25 Pascals
Measured House Leakage and Classification
CFM 50 per ft2 of surface area*
M3/h/m2 at 50 Pascals
Classification Percent of houses tested
< 0.25 <4.6 Minimal 0
0.26 - 0.45 4.7-8.2 Limited 24
0.46 - 0.60 8.3-10.9 Moderate 42
0.61 - 0.75 11-13.7 Excessive 20
> 0.76 >13.8 Major 13
* Cubic Feet per minute at 50 Pascals
Connection between home and crawl space
Mean equivalent hole size in crawl space connected areas:>in floor over crawl space 8 x 9 inches>in crawl space ducts 6.4 x 9 inches
Big Obvious Holes
Percent of total house leakage from crawl space
% of total house air leakage # of Houses (45 tested total)
31%-40% 3
21%-30% 13
11%-20% 18
0%-10% 6
Most homes had at least 10% of their air leakage coming from the crawl space
Connection between home and crawl space
Driving Forces that move air between house, crawl, and ducts HVAC equipmentStack effectWind Power attic fans
Summary of Findings
Wall vented crawl spaces have>high levels of moisture>higher amounts of mold spores than outside>holes to the living space>forces across the holes
Mold Species Measures Confirm Transmission from crawl to house
Analysis of fungal spores Species and rank order HVAC off and on 47% of houses had transmission from crawl to
house
A Robust Solution to the Vented Crawl
Specifications at www.crawlspaces.org
Closed Crawl Spaces Provide Dry Foundation and Energy Savings
Properly closed crawl space> Air seal floor and HVAC ducts>Substantially drier
▫Less potential for mold▫Less potential for wood decay▫Less potential for insects
15 to 18% lower HVAC energy use per year
Lets Be Safe Out There!
20,000 lung cancer deaths /year related to radon (U.S. EPA)
Always test for radon Especially in closed crawl spaces
Citation Information
Paper from ASHRAE IAQ Conference Malkin-Weber, M., J.Coulter, T. Dixon, C. Dastur
and B. Davis. 2007. Vented crawlspaces as mold amplification and delivery systems? Measured performance and a dry alternative. Indoor Air Quality 2007: Healthy and Sustainable Buildings (on CD)
available at www.crawlspaces.org (follow link under Technical Reports)
Melissa Malkin-Weber
919 857-9000 [phone] 919 832-2696 [fax]
909 Capability Drive, Suite 2100Raleigh, NC 27606-3870
Thank You