Rigid Insulation Under Floor Joists

Joist bays the open spaces between floor joists are prime hosts for insulation under specific circumstances.

Rigid insulation under floor joists.

At least 25mm of the joist must be left exposed to ensure air circulation. 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. Less than the height of the rim joist. But it is important to know how to install foam board insulation properly.

Without a thick layer of rigid insulation on the underside of the. This is to prevent the joist. 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.

U 0 19 in cold climates and r 20 metric system. Instead of installing the foam insulation between floor joists in the crawl space the foam board is installed against the crawl space foundation walls. You want it snug but not to. Rigid foam is the best insulation for rim joists.

But insulating your floors is a good idea for many reasons including energy efficiency and height adjustments. U 0 28 in mixed climates. We chose 2 in thick r 10 extruded polystyrene don t use expanded polystyrene which is a less effective air and moisture barrier. When the basement or crawl space has vents installed insulating joist bays.

Cut the foam into 8 ft long strips 1 8 in. Consider levels of floor insulation of about r 30 metric system. Here s what you need to know. Step 1 build the floors.