NO-94-19-3 -- Reduction of Moisture in Wood Joists in Crawl Spaces - A Study of Seventeen Houses in Southern New Jersey PDF

A study of crawl space moisture of 17 single-family houses in southern New Jersey indicates that a combination of adding a moisture barrier (polyethylene) to the bare soil and foundation walls, closing foundation vents, and sealing air leaks at the rim joist reduces moisture content of exposed floor joists by 3% to 5%, while just applying the moisture barrier reduces moisture content by about one-half that amount. Moisture content in the joists varied between 10% and 23% during the year-long study. Seven houses served as controls, while five were treated with the moisture barrier alone and five as just described. Effective air leakage area between the crawl space and outside, the house and the crawl space, and the house and outside were determined for the latter group. A strong correlation was found between moisture content and effective air leakage area between the crawl space and outside.

KEYWORDS: moisture, water content, crawl spaces, floors, USA, moisture barriers, polyethylene, foundations, walls, damp proofing, air infiltration, housing.