After a hailstorm, roofs across a neighborhood often get inspected within days of each other, and it is common for different inspectors to reach different conclusions about the same marks on the same shingles. Much of that disagreement traces back to the difficulty of telling true hail bruising apart from other marks that can look similar from a distance, particularly heat blistering and mechanical scuffing.
A true hail bruise on an asphalt shingle typically shows a random distribution that does not follow any pattern related to the roof layout, with granule displacement that exposes the asphalt mat underneath. Pressing gently on the spot often reveals a soft or spongy feel compared to surrounding areas, sometimes with a visible crack in the mat. Hail marks generally correspond to the size and force of the stones that fell, which is why hail damage tends to be denser on slopes that faced the storm than on sheltered slopes.
Heat blisters are a different phenomenon entirely, formed during manufacturing when trapped gas or moisture in the asphalt expands as the shingle heats in the sun, eventually popping and leaving a small crater with granules still largely intact around the edges. Blisters often appear in clusters or rows tied to how a particular shingle was produced, rather than scattered randomly the way storm driven hail lands, and blisters are unrelated to hail even though a popped blister can resemble a mark when viewed from a distance.
Mechanical scuffing is a third possibility. Foot traffic during installation or later roof work, ladders, or equipment can dislodge granules in linear or localized patterns, often concentrated near valleys, ridges, and roof access points, again without the random distribution a hailstorm produces across an open roof plane.
Because these three conditions can resemble each other on sight, appraisers and roofing professionals commonly use test squares, marked off sections of roof examined closely and sometimes outlined for reference, to count and characterize damage indicators within a defined area. Test squares create a consistent, documented sample that can be compared slope to slope and, where needed, reviewed by more than one party, rather than relying on a general impression formed while walking the roof.
Two inspectors can reasonably reach different conclusions if one is trained to distinguish blister craters from bruises and the other is not, or if a roof carries a mix of storm damage layered over pre existing wear. An appraisal panel works through that by relying on the physical characteristics at the mat, the granule loss pattern, the distribution across the roof, and documented test squares, forming an independent opinion grounded in what the material itself shows rather than assuming any single explanation in advance.
This article is general education about how the appraisal process commonly works. It is not legal advice, and specific procedures can vary by state and policy.
Russ Lis is a working property insurance appraiser and umpire based in Minnesota, serving clients nationwide. His construction background supports an independent, evidence based opinion on scope and value in property insurance disputes. Contact Appraisal Resolution.