Because crawl spaces are mostly buried in the ground, it's important to keep them from getting wet. Brush-on damp-proofing — or even better, dimple mats — help keep basement walls dry. Basement walls should be backfilled with coarse granular material to interrupt capillarity and to help ground- and stormwater flow toward the footing drains.

Crawl spaces have all of the disadvantages of basements and few of their advantages: they provide all of the moisture, mold, and air leaks without providing any living space in return. Still, a crawl space sometimes makes sense. Crawl space walls should be insulated at the perimeter with rigid foam, and sealed rather than vented. The best current practice is to make a crawl space a conditioned area like the rest of the house. This is permitted by newer versions of most building codes, and is much better for the house and the people who live there.

Insulation on the inside or outside?Crawl space foundations need insulation on either the inside or the outside. Placing insulation on the outside puts the thermal mass where it can do the most good — inside the thermal envelope. But the above-grade portions of exterior insulation need to be covered for aesthetic and functional reasons; providing this protection is an added hassle and expense. Insulating the inside allows the insulation to be continuous from the slab to the floor framing, but puts the thermal mass outside the insulation.

Enclosure overview

Crawl spaces

Footing Drains