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

mweber@advancedenergy.orgwww.advancedenergy.org

919 857-9000 [phone] 919 832-2696 [fax]

909 Capability Drive, Suite 2100Raleigh, NC 27606-3870

Thank You