Ever wonder why your floors feel cold in January even after you've insulated the attic? The culprit is probably your rim joist โ the band of framing that sits right on top of your foundation wall. It's one of the most air-leaky spots in any Northeast Arkansas home, and most people never think about it.
A typical uninsulated rim joist cavity loses more conditioned air per linear foot than a drafty window. In Climate Zone 3 (that's us โ Jonesboro, Trumann, all of Craighead and Poinsett counties), the IRC R402.1.2 table calls for a minimum R-15 in rim joists. Most older homes have exactly zero.
Closed-cell spray foam is the gold-standard fix here. A 2-inch lift of 2-lb closed-cell hits R-14 and, more importantly, air-seals the cavity completely. We typically see installed costs of $1.75โ$2.50 per board foot in this area, and most full rim joist jobs on a 1,500 SF footprint run $400โ$900 โ a one-time cost that pays back in lower Entergy bills every July and January.
Why not just stuff in a batt? Fiberglass batts won't air-seal. Humid summer air sneaks in around the edges, condenses on the cold foundation, and you're on your way to a mold problem. Spray foam seals and insulates in one step โ no separate vapor barrier needed at that location.
If you've been putting this off, July is actually a great time to schedule it. Crews can access crawl spaces before the heat really peaks in August, and you'll feel the difference on your October electric bill.
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