How To Insulate Cantilevered Floor Joists

Plywood subflooring above the cantilever should be caulked at the edges and seams.

How to insulate cantilevered floor joists.

Floor cantilevers constructed in accordance with table r502 3 3 1 shall be permitted where supporting a light frame bearing wall and roof only. Bay window and floor deck cantilever insulation details. Cellulose cantilevered floor insulation. It s better for the blocking to be on the interior side of the bearing wall rather than the exterior side.

Insulating foam sheathing and or house sheathing or siding should be attached to the underside of the cantilever floor joists as a protective covering. Attempts to insulate cantilevered floor joists often don t cut the mustard because cantilevered spaces are frequently stuffed with foam or fiberglass once the framing is complete almost as an afterthought. I ve written quite a few articles on how to insulate basement walls and floors but one more specific topic related to this subject keeps coming up and that s how to insulate a bay window floor or cantilever floor framing. Seal each piece of blocking at the perimeter.

Floor cantilever spans shall not exceed the nominal depth of the wood floor joist. Taking care of the insulation process while framing is still going on will prove more effective. 4b slab floors built directly on the ground. 4d extend insulation into joist space to reduce air flows.

Also insulate 4a any portion of the floor in a room that is cantilevered beyond the exterior wall below. The spray foam insulation comes in a kit that. 4c as an alternative to floor insulation foundation walls of unvented crawl spaces. The cantilever floor cavity must be filled with insulation that completely touches the underside of the floor.

Installing cellulose via the crawl space is fairly simple as it is just blowing the material into the floor joists. In addition to floors other cantilevered architectural features may require insulation. Floor cantilevers supporting an exterior balcony are permitted to be constructed in accordance with table r502 3 3 2. In this article i ll share a detail for new construction and also a detail for renovating existing bay window.

If you re about to insulate a cantilevered floor the first step is to install blocking between the joists. Usually only the cantilevered portion of the floor needs to be insulated. To air seal the floor cavity properly completely seal the band joist area and the subfloor and seal any penetrations in the floor with foam. 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.

A poorly sealed floor cavity has a significantly reduced r value and isn t much better than a floor cavity with no insulation at all. The blocking should be located above the bearing wall below.