Spray Foam Insulation in Des Moines, IA

Why insulation matters more in Des Moines than the brochure suggests

Polk County sits in IECC climate zone 5A, the U.S. Department of Energy's "cold" region, and the numbers back that up. NOAA's 1991-2020 normals for Des Moines International Airport put the January average temperature at 22.3 F with an average low of 13.8 F, roughly 128 nights a year at or below freezing, and about 10 nights at or below zero. The station's annual heating degree day total is about 6,180 (base 65 F). That is a long, hard heating season, and every gap in the thermal envelope costs you for six months instead of two.

The housing stock makes it worse. The Census Bureau's 2024 American Community Survey puts the median year built for a Des Moines home at 1963, with roughly a quarter of the city's housing units built in 1939 or earlier and nearly half built before 1960. Those houses went up before Iowa had any statewide energy code. Many have two to four inches of settled cellulose or rock wool in the attic, uninsulated rim joists, open balloon-framed wall cavities and dozens of unsealed penetrations into the attic.

Add about 36.5 inches of snow in a normal season (NOAA, same normals) and you get the metro's signature winter problem: ice dams. Warm indoor air leaks into the attic, warms the roof deck, melts snow from below, and the water refreezes at the cold eave. University of Minnesota Extension is blunt about it: "It is primarily heat flowing from the house that causes the nonuniform temperatures of the roof surface leading to ice dams." That means the fix is in the attic floor, not the gutter.

Iowa adopted the 2012 IECC with state amendments as its energy code effective June 1, 2014. It calls for R-49 ceilings, R-20 walls (or R-13 plus R-5 continuous), R-19 or R-15 continuous on basement and crawl space walls, and an air-leakage limit of 4 air changes per hour at 50 pascals for new one- and two-family homes. The code does not apply to remodeling existing houses, so nobody is going to make you meet it. But it is the clearest local benchmark for what a well-insulated Central Iowa house looks like, and it is where we aim when we scope a retrofit.

How a spray foam project works

It starts with a walk-through, not a quote sheet. We look at the attic, the rim joist, any crawl space or unfinished basement wall, and the places where heat commonly escapes: top plates, chases, recessed lights, the attic hatch, bath fan ducts, the sill and the band joist. If you have ice dams, drafty rooms, frost on the underside of the roof deck or a musty crawl space, we want to see where that is coming from before we talk products.

Then you get a written scope that says what will be sprayed, at what thickness, with which foam type, and why. Open-cell and closed-cell foam do different jobs, and so do fiberglass, cellulose and rigid board; a good scope often mixes them. If a cheaper material does the job in a given spot, the scope says so. You also get a plain explanation of prep (moving stored items, protecting finishes), ventilation during the job, and how long the house needs to air out before you are back in the space.

On install day the crew masks off the work area, sets up ventilation, and sprays in lifts to the specified thickness. Thickness is checked with a depth gauge, not eyeballed. Where the code requires a thermal or ignition barrier over foam in a living space or an attached garage, that is in the scope from the start rather than discovered by an inspector later.