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: F H 2 O pipes: F Floor: F Framing: F 85 F 60% RH 70 F DP 73 F 90% RH 70 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 houses Between years old Average 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 HousesOutside (CFU/m3) Crawl space (CFU/m3) 453,02719, ,23530, ,42716, ,033161

Is there a connection between crawl space and living space? A = outside to house B = outside to crawl space C and D = ducts to crawl space E = crawl space to house G and F = outside to ducts A E D C B 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 house B = outside to crawl space C and D = ducts to crawl space E = crawl space to house G and F = outside to ducts A E D C B House Crawl Space G return supply F Pressure tap setup measured pressures:

APT: Pressure tap setup measured pressures A E D C B house crawl space G return supply F

Measured Duct Leakage and Classification CFM 25 per ft 2 of conditioned floor area * M 3 /h/m 2 at 25 Pascals of conditioned floor area * ClassificationPercent of houses tested <3%<0.55%Minimal % %Limited % %Moderate % %Excessive18 >12%>2.20%Major65 * 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 ClassificationPercent of houses tested < 0.25<4.6Minimal Limited Moderate Excessive20 > 0.76>13.8Major13 * 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 equipment  Stack effect  Wind  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

Mean Spore Count by Location # of HousesOutside (CFU/m3) Crawl space (CFU/m3) Crawl space molds in home? 453,02719, HVAC off 1061 HVAC on 213,23530,163 Definite (47%) 861 HVAC off 1761 HVAC on 102, No (22%) 1323 HVAC off 645 HVAC on 143,42716,041 Possible (31%) 55 HVAC off 176 HVAC on

A Robust Solution to the Vented Crawl Specifications at

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 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 (follow link under Technical Reports)

Melissa Malkin-Weber [phone] [fax] 909 Capability Drive, Suite 2100 Raleigh, NC Thank You