The ins and outs of crawl space insulation


By Cold Climate Housing Research Center Staff

The “Ask a Builder” series is dedicated to answering some of the many questions Fairbanks residents have about building, energy and the many other parts of home life.

Q: I want to insulate my crawl space. Is it better to put insulation on the inside or the outside?

A: Either method will work, however the advantage to insulating on the outside is that the exposed concrete on the inside will stay warmer and be less likely to attract condensation. These are the top two problems we generally try to solve with crawl space insulation. Unfortunately, insulating on the outside is often not possible because of sidewalks, parking areas or gardens in the way.

If there is any chance moisture could get into the crawl space, which is often, choose an insulation that is water-resistant such as rigid foam board or a sprayed-in high-density polyurethane foam.

When using rigid foam board, seal the joints with an appropriate tape or spray foam sealant so air and moisture cannot move between the joints and condense on the wall behind it.

Regardless of where the insulation is put, make sure the crawl space has a good ground air/vapor barrier, such as 6-mil polyethylene. Soils can contribute a lot of moisture to a crawl space even if the ground feels dry.

It is important to cover the whole floor, and seal the air/vapor barrier to the walls, otherwise moisture will enter the space through gaps. Moisture is less of a problem in the winter when the ground freezes outside, but a lot of moisture can get in during the swing seasons and in the summer. The barrier also prevents gases, particularly radon, from entering in through the crawl space.

Q: I have unused construction materials.

Where can I take them for recycling besides one of the local transfer sites?

A: Habitat for Humanity will accept good quality building materials like doors, cabinets, or anything else used to build a house. They will even accept good quality appliances. Habitat sells these materials in their store or uses them for projects.

Before you load up your truck, contact the local Habitat for Humanity folks at 452-1685 or www. to be sure they can use your donations.

If you have any materials that cannot be recycled, the Fairbanks North Star Borough Solid Waste Department will take them for proper disposal or recycling. Common materials include appliances, paints, antifreeze, fuels and other substances.

If you have any questions, contact them at 459-1482.

Alaska HomeWise articles promote home awareness for the Cold Climate Housing Research Center. If you have a question, e-mail us at can also call the CCHRC at 457-3454.