What size hail damages a roof?

A threshold size is the smallest hail that commonly causes functional damage: a fracture, puncture or tear that reduces a roof's ability to shed water or shortens its life. The most widely cited table comes from field observations published by Haag Engineering researchers in 2002 (after Morrison 1997), with slate and clay tile added from later Haag work.

In laboratory tests on roofing aged about 11 years, organic 3-tab shingles were damaged by 1-inch ice balls half the time, fiberglass 3-tab shingles started failing at 1.25 inches, laminated shingles at 1.5 inches, and S-shaped concrete tile and gravel-surfaced built-up roofs needed 2-inch ice. Lab ice is denser than natural hail, so lab results are a worst case.

There is no published functional threshold for metal roofing comparable to the shingle table. IBHS describes impact-rated metal as likely to survive most hailstone sizes without functional damage but vulnerable to cosmetic dents. Whether cosmetic denting is covered depends on the insurance policy; some policies exclude it.

• Age and condition. The thresholds assume a roof in good or mid-life condition. Weathered, brittle shingles fail at smaller sizes.
• Hail hardness and density. Hard, dense stones transfer more energy than soft or slushy hail of the same diameter.
• Wind. Wind-driven hail falls faster and at an angle, hitting windward slopes, siding and windows harder.
• Impact angle and slope. Square hits do the most damage; glancing hits on steep slopes do less.
• Support. Shingles over gaps or soft decking break more easily.
• Temperature. Asphalt is more brittle when cold and more pliable when warm.

A single sub-1-inch storm rarely causes functional damage to a sound roof. However, 2025 research from the Insurance Institute for Business and Home Safety (IBHS) found that large numbers of small hailstones measurably degraded asphalt shingles, and that weathered specimens became roughly ten times more susceptible to later large hail. Repeated small-hail events can shorten a roof's life even when no single storm leaves obvious damage.

Contractors compare a storm's hail size with the roofing in the area. In Hail Pro you can filter the properties inside a hail swath by estimated hail size, then by roof permit history and year built, so a 1.25-inch storm surfaces neighborhoods of older 3-tab and laminated shingle roofs first. See how to find hail-damaged roofs.