About this Project

After attics, unheated crawlspaces are the next-most-vital places to insulate. You have two options: drape batts or blankets around the space's perimeter walls, or suspend material between floor joists.

Draping the walls creates a sealed air chamber, adding further insulation value. With some houses, however, you have no choice but to insulate the floor between the joists.

Wrapping up a crawlspace is a dirty but easy chore -- providing you have enough space to crawl around. You'll need unfaced batts or blankets, 6-mil polyethylene sheeting to cover the ground, 1x2s and nails, and rocks or bricks. Wear goggles and other protective gear.

Close off unnecessary openings, but don't seal vents permanently; a crawlspace needs these for "breathing" in hot, muggy weather.

Examine the underside of the floor. Joists run parallel to two walls, perpendicular to the other two. The first two drawings show the slightly different treatment for the walls that run perpendicular to the joists.

Warning: If you live in an extremely cold region, such as Alaska, the Northern Plains, or northern Maine, don't use the technique explained on this page; it could cause frost heaving that might damage your foundation. Check with local contractors or your building code department for techniques used in your area.