Rigid Foam Insulation Floor Joists

Instead of installing the foam insulation between floor joists in the crawl space the foam board is installed against the crawl space foundation walls.

Rigid foam insulation floor joists.

Rigid foam insulation uses one of three materials. Wall insulation shall begin 3 inches below the top of the masonry foundation wall and shall extend down to 3 inches above the top of the footing or concrete floor 3 inches above the interior ground surface or 24 inches below the outside finished ground. Here s what you need to know. At least 25mm of the joist must be left exposed.

We chose 2 in thick r 10 extruded polystyrene don t use expanded polystyrene which is a less effective air and moisture barrier. Wall insulation systems require that the band joist area of the floor frame be insulated. These are panels of rigid foam sold in 4 by 8 foot sheets in a variety of thicknesses from 1 4 to 2 inches it is also sold in large bundled panels joined at the ends accordion style for use as an exterior sheathing material. Unlike fiberglass rigid foam insulation does not absorb water support mold or allow air to pass through providing that joints between boards are sealed with tape.

Cut the foam into 8 ft long strips 1 8 in. Use caulk or foam sealant to seal the joint between the top. Seal and insulate using rigid foam board insulation. This method can be hundreds of dollar less than the cost of using the commercially applied spray foam.

The insulation should be pushed tight to the underside of the floorboards. Use foam sealant such as great stuff to seal the joints. Fill the ends of joist bays with rectangles cut from rigid board insulation. A do it yourself friendly method for sealing and insulating the rim joist or band joist area is to use rigid foam up against the rim joist.

That would need 90mm of rigid foam or 150mm mineral wool. Rigid foam is the best insulation for rim joists. Step 1 build the floors. The first step is to build the floor joist or to strip back the floor until you can see the joist.

A semi rigid material is generally best as it can be cut very slightly oversized and squeezed in between the floor joists thereby ensuring no draught causing gaps.