Basement Wall & Rim Joist Insulation in Des Moines, IA

Basement wall and rim joist insulation fixes one of the leakiest parts of a Des Moines area home. The rim joist is the band of wood that sits on the foundation and carries the floor framing. In most metro basements it is bare or has a loose piece of fiberglass pushed against it, and cold air leaks through all the way around the house. The concrete walls below lose heat too. Closed-cell foam handles both: it insulates, seals air and does not soak up water.

The code target

Iowa's Table R402.1.1 lists R-15 continuous or R-19 in the cavity for basement walls in Climate Zone 5. Existing houses are not required to meet it, but it is a good goal for a basement you plan to finish. Closed-cell foam at R-5 to R-7 per inch (HomeGuide) reaches that range in about three inches, leaving more room than a stud wall packed with batts.

Why not fiberglass on the walls?

Fiberglass behind plastic sheeting was a common way to finish basements, and it often goes wrong. Humid summer air meets the cool concrete behind the insulation, water condenses, and the fiberglass and framing stay damp. Foam bonded to the concrete leaves no gap for that air to reach. On a basement remodel, we foam the rim and walls first, and the framing goes in after.

Water first

The metro has a long flood history: Wikipedia records the 1993 flood that put the Des Moines Water Works under water and a levee breach in June 2008. Most basements are nowhere near a river, but many have had seepage after heavy rain. We look for efflorescence, stains and damp spots, and if water is still coming in, we tell you to fix grading, gutters or drainage first. Insulation over an active leak only hides it.

Old and new basements

Pre-war Des Moines houses may have block, brick or stone foundations, uneven walls and a rim that is hard to reach behind old ductwork; foam handles those shapes better than boards. Basements in the newer suburbs are usually poured concrete, often with a walkout wall, and many are being finished years after the house was built. That is the best time to do the rim and walls.

Fire protection

Foam plastic in living space needs a thermal barrier such as drywall, and exposed foam in places like a mechanical room or rim may need an ignition barrier coating depending on the product. We tell you what your space needs before we start. Get a free estimate