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.