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Building Science

Rim Joists

Rim Joists serve as a prop for the floor and outline the perimeter of the floor framing. They're an insulation problem area in many homes leading to cold/ warm spots, high energy bills, air quality issues and moisture damage. They're hard to see once a home is built.

What's the problem?
  • In many homes conventional insulation batts are stuffed into rim joists, but don't fit snugly around uneven surfaces or wall penetrations like cold water pipes
  • Air can move freely around and through insulation batts and into your home's interior space through area like floor registers, leading to condensation problems on cold-water pipes and on interior surfaces 
What can you do?
  • Open-cell spray foam insulation provides an excellent solution for rim joists, by expanding to fill all gaps, holes and joists to minimize air leakage and condensation issues and to provide significant energy savings. It sticks to surrounding surfaces and won't lose its R-value over time
  • If using fiberglass batts, take the time to properly cut each piece and use detailing materials to better seal air leaks and create a vapor barrier 

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