Rim Joist & Basement Insulation in Duluth, MN

Rim joist and basement insulation targets the part of a Duluth house that is easiest to forget. The rim joist, also called the band joist, is the wood frame that sits on top of the foundation wall and holds the floor joists. Above ground, exposed to the wind and usually with nothing but siding outside it, it leaks air and heat at every joint. In older houses the gaps between the sill plate and the foundation can be wide enough to feel the draft with your hand.

Why closed-cell foam

Fiberglass batts stuffed into rim joist bays do little to stop air, and warm, moist air reaching the cold wood behind them can condense. Closed-cell spray foam sticks to the wood, seals the gaps and insulates in one step, and at typical thickness it slows vapor. HomeGuide puts a rim joist foam job at about $2,000 to $2,500.

Basement walls

Concrete, block and stone foundations carry the cold of the ground into the basement. Minnesota's building rule puts St. Louis, Carlton and Lake counties in frost Zone I, where footings must go at least 5 feet deep, and the upper part of the wall sits in frozen soil all winter. Insulating the wall from the inside makes a basement easier to heat and finish. The 2012 IECC table lists R-15 or R-19 for basement walls in Climate Zone 7. Closed-cell foam handles uneven block and stone and goes on before framing.

Moisture first

We check for water before covering any wall. Efflorescence, damp spots, active leaks and poor grading outside all need attention first. Foam is not a waterproofing system, and covering a wet wall only hides the problem.

Crawl spaces

Some houses and additions sit over crawl spaces. Here we usually insulate the crawl space walls with closed-cell foam, seal the rim and lay a vapor barrier on the ground, rather than insulating the floor above. We look at the space before recommending either approach.