Crawl Space Insulation
Crawl Space Insulation

When you go to most home improvement centers looking for rigid insulation you will find several different kinds; white, white with foil, pink, blue and many others. So which is the right type to use in a crawl space? There are two actually, Dow makes the blue and Owens Corning makes the pink extruded polystyrene. Both of these are the proper rigid foam for a couple of reasons. Only the pink and the blue are treated with a fire retardant and comply with ASTM E 84, which is a smoke and flame spread test. The second reason is only the blue and the pink resist taking on moisture and at the same time have a low perm rating.

Just like there are wrong ways to install fiberglass insulation there are wrong ways to install rigid insulation. For the rigid insulation to properly do its job it has to be tight to the foundation wall. There are many foam board glues on the market but the one that works the best is an instant grab adhesive. With this product you do not need mechanical fasteners to hold the board on the wall until the glue dries, and in a crawl space that’s priceless.

To ensure your investment lasts a lifetime choose a quality vapor barrier like the SilverBack™ brand crawl space vapor barrier. This is a project that you will only want to do once in your life. It’s important that the vapor barrier is attached and sealed to the foundation above the outside grade to prevent water seepage onto the barrier. This often times means that the barrier will be installed over the rigid insulation. In the southeast it is common for the outside grade to be the same as the grade inside the crawl space. In these occasions the installer can attach the vapor barrier up the foundation wall 10-12” and install the rigid foam board over the barrier lip to the inspection gap. Check your local codes on whether your building department enforces the termite inspection gap of 3”.

Copyright© 2010 CrawlSpace Concepts LLC

Properly installing foundation wall insulation and a high performance vapor barrier in a crawl space.

Rigid Foam Board

  1. -2” thick rigid foam is R-10

  2. -1” thick rigid foam is R-5

  3. -For best performance glue rigid foam directly to the foundation wall

  4. -SilverBack™ vapor barrier attaches to the foundation over the rigid foam when:

  5. 1.Outside grade (dirt) is 10” or more over the crawl space floor

  6. 2.There is known water seepage through the foundation wall

If neither 1 or 2 are true you have this option

  1. -Attach the SilverBack™ directly to the foundation wall 10”-12” up from the footing or dirt floor

  2. -Install rigid foam insulation directly to the foundation wall allowing the bottom 10”-12” to hang over the SilverBack™


This picture shows how the vapor barrier and the rigid insulation are installed together. The rigid foam goes on the wall and then the vapor barrier is installed over it to ensure an air and moisture tight bond.