Freeze-Thaw Cycles and Roof Damage in West Michigan

We downloaded the daily high and low temperatures for the Grand Rapids airport station from NOAA's National Centers for Environmental Information and counted the days when the low was 32 degrees or colder and the high rose above 32. That is the simplest way to count a day that both froze and thawed at the weather station. For the 29 full cold seasons from July 1991 to June 2020, the period behind today's climate normals, the average was about 83 such days a season. The mildest season had 56 and the harshest had 108.

The cycles are not spread evenly. March averaged about 18 crossing days, December about 14 or 15, November about 14, February about 12, January about 10 and April about 9. October and May add a few more at either end. The official 1991 to 2020 normals for the same station tell the same story from another angle: about 133 days a year with a low at or below freezing, but only about 50 days when the high stays at or below freezing. The gap between those two figures is the freeze-thaw season.

Recent winters have stayed in that range. By the same count, the five cold seasons from 2020 to 2021 through 2024 to 2025 had 96, 90, 94, 86 and 65 crossing days. A milder winter does not mean fewer cycles. The 2023 to 2024 season had far fewer freezing nights than normal, yet still had 86 crossing days, because more of its days hovered around 32 instead of staying well below it.

Water expands by about 9 percent when it freezes. A technical bulletin from the National Institutes of Health's facilities office explains the consequence for porous and jointed materials: when water fills a void and freezes, it presses on the surrounding material, and if that pressure exceeds the material's strength, it cracks. The crack is a slightly bigger void, which holds more water at the next thaw, and the next freeze cracks it further. The bulletin notes that places where temperatures cross freezing frequently can see more damage than colder places that simply stay frozen.

On a roof, the voids are things like a nail hole that has opened around the shank, the gap under a lifted shingle tab, a hairline crack in a chimney crown, a dried-out sealant bead that has pulled away on one side, or a split in a pipe boot collar. None of these needs to be large. It needs to hold a little water at a thaw and then freeze. Do that 80 times and a gap you could not see in October can be a drip by April.

Movement adds to it. Wood, metal, brick and asphalt all expand and shrink with temperature, by different amounts. Every cycle moves a flashing joint, a shingle over a deck seam, or a step flashing against brick, slightly out of step with its neighbor. Mechanical laps tolerate that. Glued and caulked joints are asked to stretch and compress every time.

An ice dam is freeze-thaw concentrated at the eave. The University of Minnesota Extension describes the conditions: snow on the roof, the upper part of the roof surface above 32 degrees and the lower edge below it. Snow melts higher up, the water runs down under the snow, and it refreezes at the cold overhang. Each melt adds to the ridge of ice, and water held behind it can back up under shingles that were only ever designed to shed water running downhill. ARMA describes ice dams the same way, as repeated thawing and freezing of melting snow.

Extension's guidance is that the heat usually comes from the house, mostly through air leaks into the attic, and that the long-term fix is sealing those leaks and then adding insulation. Ventilation that keeps the deck cold from eave to ridge helps too. Those are attic and insulation jobs. The roofing side is the ice barrier, which limits how much damage a dam can do while the heat problem is solved.

The 2015 Michigan Residential Code addresses this directly in Section R905.1.2. In areas with a history of ice forming along the eaves, it calls for an ice barrier of two layers of underlayment cemented together or a self-adhering polymer modified bitumen sheet, running from the lowest edge of the roof to at least 24 inches inside the exterior wall line, and on roofs of 8 in 12 or steeper, at least 36 inches up the slope from the eave. Michigan's version of the code answers yes to ice barrier statewide in its climate table. A repair at the eave should restore that protection, not just replace the shingles over it.

The general rule is simple. A freeze-thaw climate rewards repairs that shed water by overlap and mechanical fastening, and it punishes repairs that depend on a single glued line. That shapes what to ask for when something needs fixing.