Foam Board Insulation Between Floor Joists

If you re ready to insulate the rim joists in your basement or crawlspace you have to decide between rigid foam and spray foam.

Foam board insulation between floor joists.

4d extend insulation into joist space to reduce air flows. Once the glue is dry and all the foam board insulation is installed you can seal around the foam boards with caulk. Place more foam board pieces perpendicular on top of the joists. Place the foam board against the rim joist and seal around the remaining edges with the spray foam.

If there are problems with the board staying in place a bead of foam board adhesive can be. If you don t want to use fiberglass remember too that you could substitute mineral wool batts or cellulose for the fiberglass. Instead of installing the foam insulation between floor joists in the crawl space the foam board is installed against the crawl space foundation walls. I think with his method i can achieve 6 8 inches of foam.

Dry fit the rigid foam board pieces. That means that as long as you ve done a perfect job air sealing the rim joist you can omit fluffy insulation between the joists assuming that you would be satisfied with r 16 performance. Rigid foam is the best insulation for rim joists. Also insulate 4a any portion of the floor in a room that is cantilevered beyond the exterior wall below.

4b slab floors built directly on the ground. Place back between the joist and hold it in place for five seconds or for how long the instructions on the glue says. Two story homes usually have another ring of rim joists above the first floor ceiling. Use spray foam to seal the foam between the joists this will both insulate and create my air barrier for this portion of the attic.

Rigid foam is affordable. You want it snug but not to. We chose 2 in thick r 10 extruded polystyrene don t use expanded polystyrene which is a less effective air and moisture barrier. If you need to insulate these rim joists it s best to hire a cellulose insulation contractor.

The best insulation material for crawl spaces is rigid foam insulation board. When the basement or crawl space has vents installed insulating joist bays. If it you need to spread it use a brush to help cover and smooth out the glue. Cut foam board to fit in between joists.

Joist bays the open spaces between floor joists are prime hosts for insulation under specific circumstances. Prior to placing the foam board in place run a bead of expanding foam along the bottom of the rim joist cavity. 4c as an alternative to floor insulation foundation walls of unvented crawl spaces. You can insulate second floor rim joists following the same steps shown here if you happen to tear out a ceiling during remodeling.