Fan Door Testing on Crawl Space Buildings

Abstract

In order to learn something about the leakage characteristics of crawl spaces, a small-scale investigation was made using fan doors on nine buildings in Tennessee. This effort was part of a larger project to study the control of indoor radon levels in crawl space houses. The goal was to gain insight into the overall leakiness of crawl spaces and the leakage between the crawl spaces and the living spaces. The investigation made first order estimates of the effective leakage areas (ELA) of the crawl spaces and the floor areas between them. It was discovered that, even with passive vents closed, crawl spaces are quite leaky compared to the building shell they support, and that the leakage area between the unconditioned crawl spaces and the conditioned upper part of the building were also large.

Indoor Radon Reduction in Crawl-space Houses: A Review of Alternative Approaches

“…The effective leakage area of crawl spaces will vary depending upon crawl-space size, foundation wall material (commonly hollow block vs. poured concrete), and method of construction. Blower door testing in nine crawl-space houses in Tennessee having an average floor area of 164 m2 and having hollow block foundation walls, showed that the average effective leakage area of the crawl spaces (1,690 cm2) was greater than that of the living areas (1,064 cm2), even with the crawl-space foundation vents sealed (Brennan et al, 1990). The crawl-space leakage area included an average of 355 cm2 in the floor between the crawl space and the living area, sugges-ting that the remaining 1,335 cm2 was associated with the foundation wall.…”

“…Typical crawl spaces, with relatively leaky floors and foundation walls, were reported to have specific leakage areas of 8 to 13 cm2/m2 in one house with the vents closed (Turk et al, 1987) and in nine houses with the vents sealed (Brennan et al, 1990). Unless that leakage area can be substantially reduced as part of the installation, it would be expected that crawlspace depressurizations relative to the living area will commonly be a fraction of a pascal, at best, with the maximum exhaust flows that can be generated by a standard 90 W mitigation fan when it is connected into any piping (60 to 80 Vsec).…”

“…Sealing standard 20 by 41 cm foundation vents will reduce the measured effective leakage area by about 130 cm2 for each vent, relative to the leakage when the vent is wide open (Brennan et al, 1990;Pyle and Leovic, 1991). This is significantly less than the gross area which would be calculated from the dimensions of the vent (820 cm*).…”

“…In the one house for which these data are available (Brennan et al, 1990), the effective leakage area of the block crawl-space foundation wall when the 10 vents were open was about 2,720 cm2. Less than half (1,290 cm2) was associated with the open vents.…”

“…Crawl-space foundation walls can sometimes be fairly leaky even without vents. In the one house from which data are available (Brennan et al, 1990), unsealing ten 20 by 41 cm vents approximately doubled the effective leakage area of the foundation wall, increasing it from 1,430 to 2,720 cm2 (129 cm2 per vent).…”