Rigid Insulation Under 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 insulation under floor joists.

Joist bays the open spaces between floor joists are prime hosts for insulation under specific circumstances. Consider levels of floor insulation of about r 30 metric system. When the basement or crawl space has vents installed insulating joist bays. 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.

Step 1 build the floors. Rigid foam is the best insulation for rim joists. Recommended under floor insulation levels. But insulating your floors is a good idea for many reasons including energy efficiency and height adjustments.

The insulation should be pushed tight to the underside of the floorboards. At least 25mm of the joist must be left exposed to ensure air circulation. Here s what you need to know. U 0 19 in cold climates and r 20 metric system.

You want it snug but not to. 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 28 in mixed climates. Without a thick layer of rigid insulation on the underside of the.

We chose 2 in thick r 10 extruded polystyrene don t use expanded polystyrene which is a less effective air and moisture barrier. Cut the foam into 8 ft long strips 1 8 in. Less than the height of the rim joist. The first step is to build the floor joist or to strip back the floor until you can see the joist.