Is your crawl space making your home unhealthy?

Is your crawl space making your home unhealthy?
November 21, 2011 - Sean Canning

Maintaining a suitable indoor air quality is critical to sustainable design and occupant health. One largely overlooked area that can be critical to the indoor air quality are crawl spaces. Particularly in renovations and remodels these spaces are designed or constructed improperly.

Basically, to avoid creating a condition where mold can grow you need to always prevent moisture and provide ventilation. There are two acceptable ways to design a crawl space per 2010 California Residential Code and following general best practices with the differences being where the moisture barrier is and where the ventilation occurs. To simplify it even more, either the crawl space is treated like a conditioned room inside the home or the space remains completely part of the exterior. In both cases, the thermal barrier (insulation) and the vapor barrier (plastic lining) should always be adjacent to each other to prevent condensation (unwanted moisture).

In scenario 1: the crawlspace is insulated at the bottom and up the walls (no insulation should be between the crawl space and the conditioned space in this scenario.) The moisture barrier also is installed per code on the bottom and up the walls. Finally vents are required to transfer conditioned air from the crawlspace to the rest of the home maintaining adequate airflow to prevent mold and mildew growth (see requirements of code — attached). Plumbing and electrical penetrations are not adequate for ventilation.

In scenario 2: the insulation and vapor barrier are installed on the top of the crawl space in the floor of the home. In this case the thermal envelope does not include the crawl space. Since the crawlspace in unconditioned, ventilation needs to occur with the outside air.

California Building Code does not allow for an encapsulated, non-vented crawl space because this would create an environment that would promote mold growth. So make sure your crawl space is designed properly to avoid mold, mildew, and an unsafe indoor environment for your family.