Rim Joist Insulation Benefits

What is a rim joist? 

In a building or home, joists are the primary structure of the floor frame of a house and are supported on the ends by the foundation of the house. Rim joists are located at the top of your basement walls. They usually look like wooden squares going around the perimeter of the basement and their main purpose is to support the weight of the floor resting on the joists. In an unfinished basement or crawl space, you can see the exposed face of the rim joist between each floor joist, just above the foundation wall.


Rim Joist Insulation Benefits - Image 1


Why do rim joists need insulation? 

Rim joists are a source of considerable heat loss in the cold months but while heated air escapes through them, cold outside air is also drawn in due to the stack effect or air leaks in the attic. As warm air generated by your furnace rises through your home and escapes through the attic, more cold air is pulled in through leaks in the rim joists. This leaves your home feeling cold and drafty and this ongoing cycle leads to high heating costs. 

Sealing the attic is a good first step to stop the stack effect, but the job isn't truly complete until the basement leaks are fixed as well. 


Benefits of rim joist insulation: 

  • Lower energy bills - Keep conditioned air inside where you want it and maintain a comfortable home easier at a lower expense 
  • Improved comfort-  More consistent indoor temperatures year-round, warmer floors, and fewer drafts
  • Healthier environment- Better moisture control and indoor air quality, less energy consumption, and a lower carbon footprint


What materials do we use to insulate rim joists?

The professionals at Comfenergy typically use spray foam or foam board to insulate rim joists. Spray foam is one of the best insulation options because this two-part polyurethane foam expands to seal gaps and insulates the area effectively, stopping air leakage in one simple step. Spray foam requires an experienced installer, but the end results are worth it. Our SilverGlo foam board is another option. SilverGlo is infused with graphite (which increases the R-Value) and lined with a radiant silver barrier (which reflects heat back into the crawl space or basement). Once the board is cut to size and fit in place, spray foam seals gaps around the edges. 


Rim Joist Insulation Benefits - Image 2   Rim Joist Insulation Benefits - Image 3

If you are ready to get your rim joists insulated or want to learn more, contact Comfenergy today! Call 1-800-604-2252 or visit us at