Rim Joist & Foundation Wall Insulation in Yonkers, NY

Rim joist and foundation wall insulation deals with the band of framing that sits on top of the foundation all the way around the house. In most Yonkers and Westchester basements the rim joist is bare wood, or has a loose fiberglass batt stuffed against it, and the sill plate below it sits on uneven stone or block. Cold air comes in along that seam on every wall. You feel it as cold floors on the first story, drafts at baseboards and pipes that freeze on an outside wall.

Why closed-cell foam

Closed-cell spray foam bonds to the rim, the sill and the top of the foundation in one pass, sealing the gaps and insulating at the same time. HomeGuide rates it at R-5 to R-7 per inch. Because it slows vapor and does not absorb water, warm basement air cannot reach the cold rim and condense there, which is the moisture problem fiberglass batts tend to cause. Two to three inches covers most rims. Rigid foam board cut to fit and sealed at the edges is a cheaper alternative where the bays are regular.

Foundation walls

Many houses around here have stone or block foundations, often with old parging and occasional dampness. Before insulating any foundation wall we look for water: efflorescence, stains, damp spots, a sump that runs often, or a history of flooding. Insulation does not fix a leaking wall and can hide one. Where the wall is dry, closed-cell foam or foam board keeps the concrete or stone from chilling the space and keeps humid indoor air off the cold surface. The 2025 state code summary from the Insulation Institute lists R-19, R-15 continuous or R-13 plus R-5 continuous for basement walls in new work.

Crawl spaces and partial basements

Additions, sunrooms and porches built onto older houses often sit over a shallow crawl space. Those floors are the coldest in the house. We insulate the crawl space walls and rim with closed-cell foam and put down a sealed vapor barrier on the ground, which keeps the space drier and the floor above warmer. Vented crawl spaces get a discussion first, because sealing them changes how they handle moisture.

Finishing a basement

If you are finishing the lower level, insulate before the framing and drywall go up. That is the cheapest time to treat the rim and the walls, and the stud walls can then go in front of the foam. We can schedule around your contractor.