Hail in West Michigan: What Size Damages a Roof and When to Inspect

NOAA's Storm Events Database logs hail reports filed by each National Weather Service office. For the 20 years from 2006 through 2025, the Grand Rapids office, which covers 23 counties from Van Buren and Calhoun north to Mason and Clare, logged 486 hail reports on 156 separate days. Kent County alone accounted for 45 of them. That works out to about eight hail days a year somewhere in the region, though the number swings widely: 20 in 2006 and only 2 in 2018.

Hail here is spread over a long season. April had the most reports, 93, followed closely by June with 92 and July with 83, then May with 63. September and October together added 76, and November through February still produced a few dozen reports. April's total is a reminder that hail season starts with the first strong storms after the snow melts, not in midsummer.

These are reports, not a complete measurement. A storm over farmland or at night may go unreported, and the Weather Service raised its severe hail threshold from three quarters of an inch to 1 inch in 2010, which changed what spotters tend to call in. Use the record as a floor: hail at least this often, not exactly this often.

Roof engineers use damage thresholds: the smallest hail that is likely to damage a given roof covering when it strikes squarely. A widely cited table published in the roofing consultants' journal Interface puts the threshold at about 1 inch for lightweight three-tab asphalt shingles and about 1¼ inches for heavier laminated (architectural) shingles. Those thresholds assume dense, hard hail hitting at a right angle. Softer stones, glancing blows on a shallow slope and wind-blown hail on the leeward side all change the picture.

Age matters too. Shingles get stiffer and more brittle as they lose oils and granules, so an older roof can be damaged by hail that a new one would shrug off. What hail damage looks like on asphalt is often subtle: a dark spot where granules were knocked off, sometimes with a soft, bruised feel where the mat underneath fractured. The NRCA's Professional Roofing magazine notes that granule loss from hail exposes the asphalt to sunlight, which degrades it and makes it more brittle over time, and that dents and tears can let water through to the deck.

That is why hail damage so often shows up as a leak months later. A fractured mat holds for a while, then cracks through after a winter of freeze-thaw cycles or a hot summer. If a storm dropped hail near the thresholds above, the time to find out is soon after, while the cause is clear.

Impact-resistant shingles are rated under UL 2218, which drops steel balls on a roof covering from heights chosen to match the energy of a hailstone of the same size. The Class 1 ball is 1¼ inches, Class 2 is 1½ inches, Class 3 is 1¾ inches and Class 4 is 2 inches. A product passes if no opening, such as a tear, fracture or crack, shows on the back of the shingle. The Insurance Institute for Business & Home Safety points out the limits: crushed or knocked-off granules, dents and marks visible only on top are not failures under UL 2218, and its pass criteria do not necessarily match what insurers use to decide whether to repair or replace a roof.

IBHS has since built a separate test using laboratory-made hailstones that rates shingles excellent, good, marginal or poor for tears, dents and granule loss, and Professional Roofing reports that not all products sold as impact resistant perform equally. In short, a Class 4 shingle is generally tougher than a standard one, especially against the 1 to 2 inch hail that makes up most of West Michigan's severe reports, but it is not hail proof, and cosmetic damage can still occur.