Ever wonder why your floors feel cold in January even after you've insulated the attic? The culprit is probably your rim joist โ that narrow band of framing that sits right on top of your foundation wall. It's one of the most air-leaky spots in the entire house, and most homeowners have never heard of it.
A typical uninsulated rim joist leaks roughly the same amount of conditioned air as leaving a window cracked open year-round. In Northeast Arkansas, where July heat indexes push past 105 ยฐF and January nights drop into the teens, that's a punishing two-season problem.
The fix is straightforward: cut-and-cobble rigid foam (R-10 to R-15) sealed at the edges, or โ our preferred method โ a 2-inch shot of closed-cell spray foam directly against the joist bays. Two inches of closed-cell hits about R-13 and, critically, acts as both insulation and air barrier in one pass. No gaps, no tape to fail later.
Cost-wise, a typical Jonesboro or Trumann home runs 80โ160 linear feet of rim joist. At roughly $1.50โ$2.25 per board foot installed, most rim joist jobs land in the $400โ$900 range โ often the highest ROI insulation upgrade dollar-for-dollar. Utility savings of $15โ$35 per month are common, meaning payback in under three years.
IRC R402.2.1 requires rim joists in new construction to meet the same thermal envelope requirements as the surrounding wall assembly, but millions of existing homes were built before that standard tightened up. If yours was built before 2012, there's a good chance yours is bare wood.
Reply or DM us for a free rim joist estimate โ we serve Jonesboro, Trumann, Paragould, and the surrounding NEA area.