North Carolina Crawl Spaces Vented and Closed

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North Carolina Crawl Spaces Vented and Closed
ACI Home Performance 2008 Melissa Malkin-Weber
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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

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The Myth of Vented Drying
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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?

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Study Population
45 houses Between 2 - 60 years oldAverage age 27
years
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Detailed Characterization Protocol

• Observational
• Wood moisture
• Fungal sampling
• Building Pressure Diagnostics
• Measure fungal transmission to the living space

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Crawl Space Observational Results
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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

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Moisture Data Wood Rot Conditions

• Visible wood rot 47 of homes
• Wood moisture content gt25 seen in over 1/3 of
  homes (supports wood rot)
• Wood moisture content gt19 seen in another 36 of
  homes (mold supporting)

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Visible Mold Examples
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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

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Average Spore Counts Higher in Crawl than Outdoors
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Is there a connection between crawl space and
living space?
Pressure tap setup measured pressures
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
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Is there a connection between crawl space and
living space?
Pressure tap setup measured pressures
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
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APT Pressure tap setup measured pressures
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Measured Duct Leakage and Classification
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Measured House Leakage and Classification
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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

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Big Obvious Holes
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Percent of total house leakage from crawl space
Most homes had at least 10 of their air leakage
coming from the crawl space
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Connection between home and crawl space

• Driving Forces that move air between house,
  crawl, and ducts
• HVAC equipment
• Stack effect
• Wind
• Power attic fans

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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

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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

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Mean Spore Count by Location
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A Robust Solution to the Vented Crawl

• Specifications at www.crawlspaces.org

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Closed Crawl Spaces Provide Dry Foundation and
Energy Savings

• Properly closed crawl space
• gt 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

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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

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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)

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Thank You
Melissa Malkin-Weber mweber_at_advancedenergy.org www
.advancedenergy.org 919 857-9000 phone 919
832-2696 fax 909 Capability Drive, Suite
2100 Raleigh, NC 27606-3870