Insulating Cantilevered Floor Joists

Seal the perimeter of each piece of foam with caulk or canned foam.

Insulating cantilevered floor joists.

The illustration shows rigid foam at the top and bottom of the joist bays. Installing cellulose via the crawl space is fairly simple as it is just blowing the material into the floor joists. You should only put in fiberglass insulation if you can access the cantilevered floor joist from a basement or crawl space. Install insulation without misalignments compressions gaps or voids to fill the cantilever floor cavity making full contact with the top bottom and sides of a cantilevered floor cavity cover the bottom of the insulated cantilever floor cavities with a rigid weather resistant solid blocking material such as plywood or house siding.

Cover the horizontal surface of the overhang as well as the joints where the horizontal surface comes into contact with the air dams. This material has a few drawbacks as it still allows some airflow through the floor and is known to trap allergens and moisture which can leave you with mold growth. Cellulose cantilevered floor insulation cellulose insulation can be installed in the cantilever floor joists two ways through access from the crawl space or by drilling holes through the bottom of the overhang. 4c as an alternative to floor insulation foundation walls of unvented crawl spaces.

You can insulate cantilevered floors many ways. Block and seal any open floor joists abutting the cantilever floor cavities. Apply spray foam insulation to the bottom edge of the overhang. 4b slab floors built directly on the ground.

At the top of the joist bays insert narrow rectangles of rigid foam between each joist and secure that foam to the subfloor with a compatible adhesive.