Insulation Between Floor Joists Over A Crawl Space

If your space has them avoid adding insulation to the crawl space walls.

Insulation between floor joists over a crawl space.

This type of insulation allows for conditioned air to be introduced into the crawl space. 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. Use caulk or foam sealant to seal the joint between the top of the crawl space wall and the sill. However the insulation needs to be treated with a fire retardant.

In moderate or dry climates without the threat of sustained subfreezing temperatures insulation between floor joists makes sense. Joist bays the open spaces between floor joists are prime hosts for insulation under specific circumstances. Stapling fiberglass batts between joists to the underside of your home s floor presents a number of problems. Don t compress the insulation as it requires its loft in order to maintain its rated r value.

If the crawl space is ventilated which is ideal because it aids in the elimination of moisture then fiberglass insulation can be easily installed under the subfloor between the floor joists. Floor insulation for moderate climes popular reads. Instead install fiberglass batting between the joist bays which are the spaces between each set of 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.

While this method does work in the very short term moisture eventually builds in the crawl space and grows on this highly porous surface. Department of energy recommends r 11 3 insulation under floors in warm climates and an r 25 6 to 8 in cold climates. Moisture laden fiberglass becomes heavier and begins to sag and fall. This type of crawl space also allows insulation with an r value of 19 installed in the floor joist if the crawl space and has a permanently installed dehumidifier.

Crawl space insulation basics. Where winter temperatures are extreme opt for insulating the walls and sealing off the crawl space entirely. Fiberglass insulation batts or rolls are the most economical and easiest diy choice for insulating between the floor joist in a crawl space.