TL;DR
Rim joist insulation is the air-sealing and thermal treatment of the band of framing where the floor system meets the foundation, a notorious leakage path that standard wall insulation never reaches. Best practice is two-part closed-cell spray foam or caulked-in rigid foam blocks, both of which seal and insulate in one step; fiberglass alone is discouraged there because it lets humid air reach the cold wood and condense.
What it means
Rim joist insulation is the air-sealing and thermal treatment of the band of framing where the floor system meets the foundation, a notorious leakage path that standard wall insulation never reaches. Best practice is two-part closed-cell spray foam or caulked-in rigid foam blocks, both of which seal and insulate in one step; fiberglass alone is discouraged there because it lets humid air reach the cold wood and condense. Sealing this band is among the highest-return tasks in an energy retrofit.
Where it sits in the glossary
Rim joist insulation is part of the Trade jargon group inside the ProFix Directory glossary. Browse every term in this category from the glossary index.
Why Ohio homeowners should know it
This is a term Ohio homeowners encounter when reading contractor quotes, hiring paperwork, or inspection reports. Understanding it well enough to ask one good follow-up question is usually all the protection a homeowner needs.
ProFix Directory keeps definitions short on the index page and saves the longer context — Ohio-specific rules, where the term comes from, and which ProFix tools touch it — for these per-term pages so the term is easy to cite and easy to share.
ProFix tools that touch this term
See also
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