Crawl Space Ventilation and Ground Cover

Crawl space walls below the level of the outside finished grade must be dampproofed. Install drain pipe around the footings and connect it to a sewer, ditch or dry well. Slope crawl space floors and access trenches toward the floor drain. For unheated crawl spaces, install a ground cover of concrete, asphalt or 0.15 mm (6 mil) polyethylene or Type S roll roofing over the ground surface with the joints lapped at least 100 mm (4 in.). For heated crawl spaces, install a 0.15 mm (6 mil) polyethylene sheet with joints lapped at least 300 mm (12 in.), sealed and weighted down, or, covered with at least 50 mm (2 in.) of concrete. The ground cover prevents ground moisture from entering the crawl space area. The crawl space must be conditioned like the remainder of the house, or ventilated (see Chapter 20), in which case the floor above must be insulated and be provided an adequate air barrier system and vapour barrier.

Source : Canada Mortgage and Housing Corporation (CMHC)