How to Stop Air From Moving Through the Home's Rim Joist

Monday, June 12th, 2017 by Ron Perez

Some homes with unconditioned space under the house lack the insulation necessary to stop outside air from moving into the basement or crawl and the rest of the house. The 'rim joist' is the perimeter of your floor's framing system. It is only a 2" thick wooden board that is standing between your basement or crawlspace and the outside elements. For this particular home, the amount of air that was passing through the rim joist caused their floors that were above the crawlspace to feel unbearably cold.

Uninsulated Rim Joist

Bare rim joists as shown above can allow air to move from outside of a home and into the basement or crawlspace.


Illustration of Air Movement Through Rim Joist

This photo illustrates how air can pass through this area if not insulated and air sealed properly.



Solution: For this challenge, Dr. Energy Saver has a simple fix. We install two part expanding spray foam to stop the movement of air from the outside to the inside crawlspace or basement. All cracks and gaps are filled creating an airtight seal. This resulted in warmer floors for the home and the owner will end up paying less to heat their home.


Insulated Rim Joist

This image shows a properly insulated rim joist sprayed with closed cell foam to air seal the area.





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