A do it yourself friendly method for sealing and insulating the rim joist or band joist area is to use rigid foam up against the rim joist.
Rigid insulation between floor joists.
Fill gaps larger than 1 4 in.
Gaps between the insulation and the floor can lead to inefficiency and heat loss.
Cut rigid foam insulation into strips with a table saw or a circular saw.
When the basement or crawl space has vents installed insulating joist bays.
This method can be hundreds of dollar less than the cost of using the commercially applied spray foam.
Joist bays the open spaces between floor joists are prime hosts for insulation under specific circumstances.
How to finish a basement.
Cut the strips to fit between floor joists using a box cutter.
Run a bead of acrylic caulk around each section of foam to form an airtight barrier.
Instead of installing the foam insulation between floor joists in the crawl space the foam board is installed against the crawl space foundation walls.
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.