Q: I want to add venting to the crawlspace of an old house. Are there certain building code guidelines I need to follow?
A: Building code restrictions are enforced by municipalities, so you should call your local inspector’s office to determine guidelines for your area. In general, however, crawlspaces require one vent within 3 feet of each corner. The opening should be covered with 1/4-in. screen or grate. The minimum ventilation area for the crawlspace should be 1 square foot per 150 square feet of crawlspace area. Note that these rules apply to unfinished crawlspaces. No extra ventilation should be necessary for crawlspaces sealed with a vapor retarder, insulated walls, and conditioned air space with mechanical ventilation.