How to Insulate an Elevated Floor on Cinder Blocks
The crawl space is the area between the ground and the floor joists in a house without a basement. It can be surrounded by either a poured block wall or a cinder block wall. Installing insulation in a crawl space surrounded by cinder block will reduce a home's energy consumption by controlling the flow of air through the house. You could pay a contractor to do it for you, but you'll increase your total savings if you do the job yourself.
Clear any rocks, debris or large clumps of dirt from beneath the house.
Spread the plastic sheets over the ground in the crawl space to act as a vapor barrier. The sheets should overlap by about 12 inches and extend a few inches up the wall. Place several rocks along the overlap and in the corners to hold the sheets in place. Tape the edges to the cinder blocks with duct tape.
Press the insulation snugly between the floor joists, along the length of the joists, with the paper side facing the ground. Place the insulation behind any wires or pipes; squeeze it alongside any duct, but don't crush the duct; you'll impede air flow. For maximum efficiency, there should be no space between the insulation and the wood floor. Cut insulation with the utility knife to fit any leftover space in the joist cavities.
Staple the paper flanges to the bottom of the joist to hold the insulation in place. Don't rely on friction to hold it.
Place all insulation scraps in a plastic trash bag for disposal.
- Batt insulation
- Six-mil plastic sheets
- Duct tape
- Utility knife
- Trash bag
- Wear a dust mask, goggles and protective clothing when working with fiberglass insulation.
- Be sure to purchase the correct R-value insulation for your geographic area. Most manufacturers put a map on the packaging.
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