What’s a Rim Joist and Why is it Important to Air Seal?
The construction industry uses a lot of technical jargon and homes don’t come with instruction manuals or glossaries. So what exactly is a rim joist? It is the area of a house were the foundation wall meets the floor joists. The diagram at left illustrates this nicely. This area is one of the leakiest parts of your home as often it is not sealed or insulated.
Sealing the rim joist of your home will provide a more comfortable and affordable home. This area is particularly leaky because there are many seams coming together. The more joints you have, the more potential there will be for air leaks.
Many homes we visit have fiberglass batts in there areas. While fiberglass batts are insulators they are not air sealers. Fiberglass is actually used as air filters in many applications. It is important to seal this area first before adding this type of insulation. At GIC, we use spray foam to address this area. This acts as a sealant as well as an insulator. Two benefits in one application!
You can check out more information about sealing rim joists at buildingscience.com.