Benefits Of Spray Foaming Your Home's Rim Joist
1. The rim joist area is where the foundation – which is usually cement block, poured cement, or stone – meets the wood that starts the framing of the home. This area does not seal well and is given very little air sealing attention making it one of the areas in a home that can have the most air leakage. Most homes have fiberglass or even no insulation at the rim joist area making air leakage difficult to prevent. When air does pass through the fiberglass, it can reduce the R value up to 50 percent.
2. Block foundations result in an additional drawback. This type of foundation – which happens to be the most popular – has a hollow core that is usually open at the top where it meets the top plate and the rim joist. The temperature of the ground to the frost line – approximately three feet below grade – is around the same as the outside temperature. This cold air radiates up through the open block and cools the floor along the perimeter of the home. This is one reason why the floor along the outside walls may feel considerably colder than the rest of the floor.
3. To address these issues, we use high-pressure closed cell spray foam. The foam is applied as a hot liquid. Once applied, the foam seals and insulates the rim joist, including the area where the wood top plate and the cement or stone foundation meet. The tops of all of the open blocks are also sealed. This assists in keeping the cold air locked in and prevents the floor perimeter from becoming cool. Once the air is locked in, the warmer air below the frost line – which is usually around a constant 50 degrees – will begin to warm up the cold air above the frost line. When air is trapped like this, it acts as an insulation buffer for the basement walls.
It is important to note that using two-part foam from propane size cans will not provide the same results. The foam is applied to a surface in the form of foam, not liquid. This can cause air pockets to form that prevent the foam from sealing correctly. This may also cause the foam to separate from its surface.
4. The most important issue that we try to address in any home is the prevention of air leakage. Using a closed cell foam assists us in addressing this issue. Because the foam is a closed cell foam, it acts as a vapor barrier preventing moisture. It also has an R value of 6.5 per inch.