DIY Crawl Space

Unconditioned and Vented

• As the name implies, these crawl spaces describe a raised living space with dirt beneath the flooring. These crawl spaces require sufficient drainage and a ground cover. Use an approved vapor or gas retarder to adequately cover the dirt and reduce moisture under the living space. Also install insulation within the flooring cavity that sits directly above the crawl space. Finally, consider installing an air-venting system to run between the crawl space and the living space. If you do so, make sure the venting system is adequately sealed and insulated.

Ventilation

• Each municipality has a building code that specifies crawl space ventilation requirements. Consult them before designing yours. Each building code requires that there be adequate ventilation ports for crawl spaces. Typically, the ventilation port will exist in the poured concrete foundation. Most codes require that there be a ventilation port for every 150 square feet of crawl space area. The area increases to 1,500 square feet if you use a vapor retarder. The ventilation ports or holes sit directly across from one another to create adequate cross-flow between the ports. Provide screening on each port to eliminate pest infestation.

Conditioned and Unvented

• A conditioned and unvented crawl space is more akin to a basement. Only use this design if you have an air conditioning or venting system built in the crawl space. Such a crawl space will have insulated walls and is often called a "short basement." Do not ventilate a short basement with outside air, and it must be fully enclosed. "Fully enclosed" entails completely sealing the short basement, and preventing any unwanted air from entering the crawl space. Additionally, the conditioned and unvented crawl space will have a sealed floor and you must take special care to remove any moisture that collects there.