What's a rim joist, and why should you care? It's the band of framing that sits right on top of your foundation wall, where your floor system begins. In most older Jonesboro and Trumann homes, that zone is completely uninsulated โ just bare wood exposed to whatever July humidity or January cold decides to push through.
The rim joist is one of the biggest sources of air infiltration in a single-story house. Studies from the Oak Ridge National Laboratory estimate that rim joists can account for 15โ25% of a home's total air leakage. In Climate Zone 3 (that's us, Northeast Arkansas), the IRC R402.1.2 table calls for a minimum R-15 in that cavity.
Closed-cell spray foam is the gold standard fix here. At roughly 6.5 R-value per inch, a 2-inch pass hits R-13 and โ more importantly โ acts as both an air barrier and a vapor retarder in one shot. Installed cost typically runs $1.50โ$2.50 per square foot of rim joist area, and most crawl-space or basement rim joist jobs can be completed in a single morning.
What does that get you? Floors that don't feel like ice in December. Lower humidity intrusion in summer. And a measurable drop on your Entergy or First Electric bill โ homeowners in similar builds often report 8โ12% heating-season savings after rim joist sealing alone.
If your house was built before 2000, there's a very good chance this spot has never been touched. It's a small job with an outsized return, and it pairs perfectly with an attic top-off or crawl space encapsulation if you're ready to do a full thermal envelope tightening.
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