for Cold Climate Housing and much more

Last Updated: , Created: Thursday, October 14th, 1999


The general rule is that a basement or crawl space should have at least 0.1 square meters of screened ventilation space for every 25 square meters of floor space (1 sq. ft. per 250 sq. ft.) -- that is if the floor is made of poured concrete or if a dirt floor has a ground cover. If the floor is exposed dirt then the screened ventilation should be increased to 0.3 or 0.4 sq. meters per 25 square meters (3 to 4 sq. ft. per 250 sq. ft.). Recent research has put into question the whole idea of ventilating craws spaces in the moist climate of the lower mainland of B.C. There the ventilation air is so humid that it doesn't help much and perhaps brings in more moisture than it takes out. It is the plastic ground cover (6 mil Polyethylene) that is the critical element in controlling crawl space moisture and in such humid areas building scientists are beginning to recommend covering the soil and blocking off the ventilation, summer and winter. (Reality refuses to follow simple rules.)

Crawl space ventilation should be evenly split: half on the upwind side of the house and half on the downwind side of the house. The vents should be closed as soon as the heating season starts and opened as soon as the heating system stops working regularly in the spring.

If you have a central, all-house exhaust system you don't need to make special efforts to vent a heated basement, but don't forget an unheated crawl space that is separated from the circulation of air within the rest of the house in summer as well as in winter.


Keywords: Crawl Space, Basement, Ventilation

Article 747