crawl space insulation to cool a home

Should I Install Insulation in a Crawl Space?

In a word, yes. The International Residential Code (IRC) requires crawl spaces to be insulated. Proper insulation of your home’s crawl space will benefit you financially and in several other ways.

The U.S. Department of Energy (DOE) states “A properly sealed, moisture-protected, and insulated crawl space will increase comfort, save on energy costs, improve the durability of the home, and reduce entry of moisture, radon, and other potential irritants or pollutants into the home.”

There are basically two types of crawl spaces. For decades, the standard building practice involved insulating the floor that stood over a ventilated, unconditioned crawl space. However, the IRC was recently changed to allow unvented, conditioned crawl spaces along with their financial and air-quality advantages. Regardless of whether you have a vented or unvented crawl space, it is worth it to insulate.

Insulation in Newer, Unvented Crawl Spaces

The DOE’s Building America research and development program was started in 1995 to improve construction and remodeling practices. The program’s research demonstrated that unvented crawl spaces yield an energy savings of 15%-18% while reducing humidity over 20%.

These results impacted the 2009 and 2012 versions of the IRC which now allow for unvented, conditioned crawl spaces. This design involves insulating the walls rather than the ceiling of the crawl space so that the whole area becomes a conditioned subspace. It’s basically a very shallow basement.

3 options for insulating crawl space walls:

  • Exterior foam insulation 
  • Interior foam insulation 
  • Interior batt insulation 

Additional advantages to insulating crawl space walls:

• A sealed crawl space uses less insulation material because you are not insulating the ceiling

• Ductwork and pipes are contained in the conditioned space of the house, so no insulation is required for protection against freezing or energy efficiency.

When insulating an unvented crawl space, due consideration must be given to whether a radon mitigation system is needed as well as protecting the crawlspace from pests and moisture.

Close-cell spray foam insulation

Insulation in Traditional, Vented Crawl Spaces

If you have a traditional vented crawl space with a dirt floor, you have two options:

  1. upgrade to an unvented, conditioned crawl space (insulating only the walls to create a “conditioned” space), or
  2. install subfloor insulation (insulating the ceiling of the crawl space).

Subfloor insulation can be installed as blown-in material or in batts. Blown insulation requires either a rigid or netting barrier to hold the material against the subfloor, in between the joists if they are present. Batt insulation will need a vapor retarder, and if exposed to the outside or if pests are a concern, a rigid barrier can be installed over the batts for an extra layer of protection.

batt insulation in crawl space

Proper Crawl Space Insulation Is Worth It

Most homes have crawl spaces with dirt floors, vents, and uninsulated walls. The DOE has identified the best solution is to create an unventilated crawl space and insulate the walls instead of the subfloor.

Whether you insulate under the subfloor or insulate the walls only, proper crawl space insulation will create a thermal envelope that saves energy, keeps your home more comfortable, and can discourage moisture and pest problems. Give us a call today, or learn more about our insulation services.

01 Comment

  • Elle Jones
    - at 11 months ago

    I appreciate that you detailed how adequate crawl space insulation would provide a thermal envelope that saves energy, keeps your house more comfortable, and can ward off moisture and insect issues whether you insulate under the flooring or only the walls. This advice will be very useful because my sister and I intend to construct a home for our parents. I’m hoping we can eventually locate an insulation business to perform this for the house.


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