Rigid Insulation Under Floor Joists

When the basement or crawl space has vents installed insulating joist bays.

Rigid insulation under floor joists.

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. But insulating your floors is a good idea for many reasons including energy efficiency and height adjustments. 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. You want it snug but not to.

Cut the foam into 8 ft long strips 1 8 in. Without a thick layer of rigid insulation on the underside of the. Recommended under floor insulation levels. The first step is to build the floor joist or to strip back the floor until you can see the joist.

We chose 2 in thick r 10 extruded polystyrene don t use expanded polystyrene which is a less effective air and moisture barrier. Step 1 build the floors. But it is important to know how to install foam board insulation properly. Less than the height of the rim joist.

The insulation should be pushed tight to the underside of the floorboards. Rigid foam is the best insulation for rim joists. Or rigid foam boards in floors with exposed joists open floors is straightforward. At least 25mm of the joist must be left exposed to ensure air circulation.

Consider levels of floor insulation of about r 30 metric system. U 0 28 in mixed climates. Joist bays the open spaces between floor joists are prime hosts for insulation under specific circumstances. Instead of installing the foam insulation between floor joists in the crawl space the foam board is installed against the crawl space foundation walls.