Sealing and Insulating the Rim Joist

The rim joist is an area often overlooked when it comes to home insulation, and it is also a huge source of energy loss. For those who aren’t familiar with building terms, the rim joist is the edge of the floor framing – a long plank that sits on top of the sill plate and the foundation walls. When the rim joist lacks proper insulation and air sealing, heat is lost by conductive transfer to the outside, and cold air is constantly infiltrating the basement through joints and other gaps drilled on the sill plate for plumbing, electricity and fuel lines.

In this episode of “On the Job,” Larry Janesky and his crew at Dr. Energy Saver insulate and air seal the rim joist of a home using two-part polyurethane spray foam. Closed-cell spray foam is an excellent choice for this application due to its high R-value (R-7 per inch) and expanding capabilities, which fill in holes and gaps to stop air leakage.