How to Insulate a Crawl Space

Insulation is important for keeping any home warm while controlling energy costs. One of the most important ways to keep your home warm is by insulating your crawl space.

Proper crawl space insulation also can prevent your crawl space from becoming a moist environment that grows and harbors mold and mildew. Controlling crawl space temperature and moisture is a dual process that works toward a common goal: a temperate lower area that will keep upper floors warm, while your home’s foundation remains in sound condition.

Crawl Space Insulation Basics

Stapling fiberglass batts between joists to the underside of your home’s floor presents several problems. While this method does work in the very short term, moisture eventually builds in the crawl space and grows on this highly porous surface. Moisture-laden fiberglass becomes heavier and begins to sag and fall. This outdated method is not just ineffective but regressive, as well.

Instead, a better method is the multi-pronged approach of insulating the inside walls of the crawl space with rigid foam, laying down a plastic vapor barrier over the dirt floor, then joining the two items with tape.

The idea is to condition the crawl space, much in the same way that you might condition other parts of your home. Rather than trying to cut off the crawl space from the conditioned upper floors, you should bring the crawl space nearer to upper floors’ temperatures by leaving off the underfloor insulation and by sealing the crawl space against outside moisture and temperatures.

Types of Insulation

Two-inch expanded polystyrene foam board is the favored insulation for crawl space inside walls. Rigid foam insulation works for any type of masonry wall: concrete, block, brick, and even stone.

This type of insulation may be faced with silver foil, with the foil facing inward toward the crawl space. Though the rigid foam is the chief insulator, the foil adds a bit more energy savings by reflecting heat into the crawl space. The foil, too, acts as a vapor barrier.

Crawl Space Ventilation

For this type of insulation system, crawl space ventilation to the exterior is sealed off. All avenues to the outside are shut off or sealed with caulk.

An airtight, insulated crawl space will make your house, as a whole, more energy-efficient by keeping your floors warmer in cool months and thus reducing your heating bills. During warm months, this process works in reverse by keeping your floors cooler and reducing the load on your air conditioner.