If your house was built in Livonia or Warren between 1965 and 1985, there’s a decent chance the attic still has the same pink fiberglass batts the original builder stuffed up there. That insulation was cheap then, and it wasn’t wrong for the time. But Michigan winters have a way of exposing every gap, and when Detroit area temps drop into the single digits in January, fiberglass batts sitting loose in a 60-year-old attic do not hold the line. Homeowners across Macomb County, Kent County, and the inner ring suburbs are pulling out the old insulation and putting spray foam in before the heating bills tell them to.
What Michigan Winters Actually Do to Fiberglass
The average low temperature in Detroit in January is around 20°F. Grand Rapids runs colder. Traverse City runs colder still. But the temperature number alone doesn’t tell the full story. Michigan winters combine sustained cold with high humidity and frequent freeze-thaw cycles. That combination is particularly hard on fiberglass.
When moisture-laden air moves through a fiberglass batt — and air does move through fiberglass — the fibers can absorb that moisture over time. Wet insulation loses R-value fast. A fiberglass batt rated at R-19 can perform closer to R-10 or lower once moisture gets into it. By February in a Grand Rapids home with a damp basement, you may be getting half the insulation you think you’re paying for.
Spray foam doesn’t absorb moisture the same way. Closed-cell spray foam in particular creates a vapor barrier along with the thermal barrier. For basement walls and rim joists in homes near the Great Lakes, where humidity is a constant variable, that matters. Homeowners in Dearborn, Ferndale, and Westland who’ve had spray foam applied to their basement rim joists consistently report a noticeable difference in how their basement feels by November — warmer floors, less cold air moving through the main living area.
If your Michigan home is more than 30 years old and you haven’t had the insulation looked at by someone who actually pulls out a flashlight and gets into the rim joist, it’s worth scheduling a free estimate before October. An insured contractor who works in this market knows what 1970s construction looks like from the inside, and they’ll tell you exactly where the money is leaving your house.