Crawl Space Insulation & Installation

March 10, 2023

The crawl space is the area located beneath the floor of a raised home. Crawl spaces are typically 1 to 3 feet high, as compared to basements which can be tall enough to walk around. Basements can be fully finished with flooring, lights, and HVAC, while crawlspaces are often open to the exterior with the exposed dirt as the “floor”. The “need” to insulate a crawl space and the “how” can vary greatly, based on specifics of the house and how the crawl space is constructed.


There are two distinct insulation approaches to crawl spaces – complete isolation from the home or incorporation into the conditioned space of the home.

Isolation Approach
The isolation approach considers the value of separating the dirty, moist, hot air of the crawl space from the conditioned space of the house. Since our houses have typically become more energy efficient, the “need” to insulate the floor beneath the home would seem obvious. Any such insulation should be installed in close contact with the underside of the floor system between the floor joists. The more tightly the insulation is installed, the better it will perform. For this reason, spray foam insulation is particularly effective. Because of proximity to the ground and moisture, closed cell spray insulation is preferred.

Another concern with crawl space insulation is access by insects and animals that may find the insulation attractive for nesting. Installation of wood or foam panels on the bottom side of the floor joists can provide effective protection against such infestation. Sealants installed around plumbing pipes and electrical lines is critical. Installation of a moisture barrier can significantly reduce the impact of ground moisture in the crawl space, as well.

Incorporation Approach
The incorporation approach seeks to include the crawl space within the conditioned area of the home, which mostly eliminates the concern for insulation beneath the floor in favor of insulating the perimeter of the crawl space. For this reason it is only feasible when the crawl space is enclosed by a foundation wall that can be sealed off. This also requires fully covering the floor of the crawl space with a vapor barrier, and sealing all the cracks and cervices against air leakage. This approach can be very effective but quite challenging, even in new construction.

There are various issues that can arise when dealing with air, temperature, and moisture between the crawl space and conditioned space of the home. These can be successfully managed with professional installation and the correct materials. Your local home builders association may prove to be a great resource for locating construction professionals familiar with the climate demands of your area, and for establishing the proper approach for insulating your crawl space.

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