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Built up roofing, often called BUR, and modified bitumen roofing are older but still common low slope systems, particularly on commercial buildings, additions, and multifamily properties across the Midwest. BUR consists of alternating layers of bitumen and reinforcing felt, frequently finished with a gravel or mineral surface, while modified bitumen is a related but more modern single or multi ply system, typically installed as rolled sheets that are torched, hot mopped, or self adhered. Both systems present real assessment challenges when evaluating hail impact, more so than most other roof types.
Gravel surfaced BUR is particularly difficult to inspect for hail damage because the loose aggregate covering the membrane obscures the surface underneath, and hail impacts can displace gravel in ways that look dramatic without necessarily damaging the membrane itself, or conversely can leave the membrane bruised or fractured beneath gravel that appears undisturbed. A thorough evaluation typically involves pulling back gravel in a representative sample of areas, particularly in locations showing displaced aggregate, to examine the actual membrane surface for cracking, fracturing, or granule loss consistent with impact.
Core cuts are one of the more reliable tools for evaluating BUR and modified bitumen systems, since they allow a direct look at the full cross section of the roofing assembly, membrane plies, felt layers, and insulation, at a specific location. A core cut taken at a suspected hail impact point can reveal whether the damage penetrates through multiple plies or is limited to surface granule displacement, information that is difficult to obtain through surface inspection alone. Core cuts are typically taken at several locations, both at suspected damage points and at control areas away from suspected damage, so the findings can be compared against each other rather than interpreted in isolation.
Blistering is a common condition on these roof types that is frequently confused with impact damage. Blisters form when moisture or air becomes trapped between roofing plies and expands under sun exposure, creating raised bubbles in the membrane that can look similar to hail related fracturing at a glance. Blistering develops gradually from moisture entrapment, application issues, or general aging, and it is not, by itself, evidence of a storm event. Separating blistering from genuine impact fracturing usually comes down to the pattern, since storm damage tends to correlate with hail size and directional exposure while blistering tends to appear more randomly across the roof regardless of orientation, along with what a core sample shows about whether the membrane layers themselves have actually been compromised.
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. Contact Appraisal Resolution.