Insulation Between Floor Joists Over A Crawl Space

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

Insulation between floor joists over a crawl space.

Install an air and vapor barrier over the floor and tape it to the insulation. Stapling fiberglass batts between joists to the underside of your home s floor presents a number of problems. Moisture laden fiberglass becomes heavier and begins to sag and fall. This type of insulation allows for conditioned air to be introduced into the crawl space.

While this method does work in the very short term moisture eventually builds in the crawl space and grows on this highly porous surface. When the basement or crawl space has vents installed insulating joist bays. Instead of installing the foam insulation between floor joists in the crawl space the foam board is installed against the crawl space foundation walls. 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.

Crawl space insulation basics. Don t compress the insulation as it requires its loft in order to maintain its rated r value. 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. It is important to secure insulation and cover it with a vapor barrier in order to prevent moisture and the mold that often follows close behind.

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. Instead install fiberglass batting between the joist bays which are the spaces between each set of floor joists. Use caulk or foam sealant to seal the joint between the top of the crawl space wall and the sill. Fiberglass insulation batts or rolls are the most economical and easiest diy choice for insulating between the floor joist in a crawl space.

Floor insulation for moderate climes popular reads. If your space has them avoid adding insulation to the crawl space walls. In moderate or dry climates without the threat of sustained subfreezing temperatures insulation between floor joists makes sense.