Rigid Foam Insulation Under Floor Joists

Installing fiberglass or mineral wool batts or rigid foam boards in floors with exposed joists open floors is straightforward.

Rigid foam insulation under floor joists.

They keep your home at a comfortable temperature without the need to crank your heat. That would need 90mm of rigid foam or 150mm mineral wool. Fiberglass insulation and expanding foam seal the open top of hollow concrete blocks. Next you will need to place the foam board insulation between each joist as a test.

The insulation should be pushed tight to the underside of the floorboards. Install it anywhere from the roof to the foundation. If it fits proper with no space between on either side of the board pick it up and put a thin layer of glue on. Rigid insulation is one of the best tools to reduce your energy costs.

Rigid foam insulation also known as insulating boards provide high r values. Installers should push the insulation up and fasten it to prevent any void or gap between the floor and the material. You can even place it under the foundation slab. 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.

The insulation should cover the whole depth of the cavity and contact with the floor. Airtight insulation reduces heat loss through the rim joist band joist. 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.