BUR and Modified Bitumen After Hail: Granule Loss, Fractures and Desaturation
By Blake Snow, experienced roof consultant
Built-up roofs (BUR) and modified bitumen roofs cover a lot of commercial buildings, and they are some of the hardest roofs to evaluate after hail. Gravel, cap sheet granules and years of weathering can hide damage, and they can also make an old roof look damaged when it isn't. Owners, carriers, attorneys and appraisal panels end up arguing over the same handful of questions: is that granule loss from hail or from age, is the membrane actually fractured, and does any of it affect how the roof performs?
This article walks through how an experienced roof consultant approaches those questions on asphalt-based roofs. It covers the roof side only, not coverage or legal questions.
A quick look at the systems
A built-up roof is several plies of felt or fabric laid in hot bitumen, usually finished with gravel or a cap sheet. Older roofs may use coal-tar pitch; others use asphalt. A modified bitumen roof uses polymer-modified asphalt sheets, usually two or more plies with a granule-surfaced cap sheet. SBS sheets are typically set in hot asphalt or adhesive or self-adhered, and APP sheets are typically torch-applied. Our roof systems guide covers these in more detail.
The system matters because each one shows hail differently. Gravel can absorb impacts that would mark a bare cap sheet. A cap sheet that has lost much of its granule surface to age has less protection than a new one. And the condition of the bitumen, whether it is still flexible or has become brittle with age and sun, affects how it responds to an impact.
Granule loss: the most argued-over sign
On granule-surfaced modified bitumen, hail often knocks granules loose and leaves dark spots where the asphalt is exposed. The problem is that granules also come off over time from weathering, foot traffic, ponding and maintenance. So a consultant asks:
- Is it random and spread across the roof, the way hail falls, or concentrated along walkways, drains, equipment and low spots?
- Are the spots fresh or weathered? Newly exposed asphalt tends to look different from areas that have been bare for seasons.
- Does it match collateral evidence? Dents and spatter marks on rooftop equipment, vents, edge metal and other soft metals help show whether hail of meaningful size hit that roof. Our article on dating hail damage explains how that evidence ties marks to a storm.
- Is there anything under the spot? Granule loss on its own may be cosmetic. Granule loss over a fractured or crushed sheet is a different finding.
Fractures in the membrane and reinforcement
The more important question on asphalt-based roofs is usually whether hail fractured the membrane or its reinforcement. A fracture may not show on the surface at all, especially under gravel or a granule surface. A consultant will look for soft spots, cracking that radiates from an impact, and tears or splits in the cap sheet, and then confirm with samples where the evidence calls for it.
A small test cut or sample, taken at a suspected impact and properly repaired afterward, lets the consultant look at the underside of the cap sheet or top ply and at the reinforcement inside it. Fractured reinforcement or a cracked ply under an impact point is strong evidence. A sample that shows an intact sheet under the mark is equally important, because it tells everyone the mark may be surface-only.
What "desaturation" means, and why it needs proof
Some reports describe hail impacts on asphalt roofs as causing "desaturation," meaning the bitumen at the impact has been crushed, displaced or pushed away from the reinforcement. Whether that has happened, and whether it affects the roof's water-shedding ability or service life, is something a report should show with photos and samples, not assume. A good report explains what was seen at each sampled impact and why it does or doesn't count as damage.
Gravel-surfaced BUR
On gravel-surfaced built-up roofs, the gravel can hide what's underneath. Displaced gravel, exposed bitumen and marks on the flood coat are worth noting, but they aren't the same as a fractured ply. Consultants often have to scrape gravel back at sample locations to see the surface below, then decide whether a test cut is needed. Older BUR roofs also tend to show age-related problems that look nothing like hail: blisters, alligatoring, splits along felt joints, and ponding areas. Those need to be separated from storm damage, not lumped in with it.
Age, brittleness and prior condition
An old asphalt roof can still be damaged by hail. In fact, a brittle, weathered sheet may fracture more easily than a new one. But age also produces cracking, granule loss and splits on its own. That's why prior reports, repair records, warranty files and photos matter. They help show what the roof looked like before the storm and whether the condition being claimed was already there. Our article on policy-first review covers why we check the policy before the roof work begins.
Water after hail
If hail fractured the membrane, water may already be in the insulation. Drone inspections and infrared inspections to find water infiltration help show where wet insulation is, and core cuts confirm what a scan suggests. Separating storm-related water from long-standing leaks is part of the causation question.
What a good BUR or modified bitumen hail report includes
- The roof system, surfacing, number of plies where known, and overall condition
- A roof plan with test squares or inspection areas and sample locations marked
- Photos of each sampled impact, from the surface through the sample
- Collateral evidence on equipment and soft metals, with photos
- For each finding, whether it is functional damage, cosmetic, or unrelated wear, and the reasoning
- What was not damaged, which matters as much as what was
- How sample cuts were repaired
For more on reports, see our roof inspection reports page and our hail damage expert page. Single-ply roofs show hail differently; our article on hail damage on TPO, PVC and EPDM covers those.
Why we call it straight
Blake has spent 30+ years on roofs, from a family with 80+ years of roof consulting, and has inspected and reported on thousands of roofs on buildings from 10,000 sq ft to multi-million sq ft. On asphalt roofs, the evidence sometimes supports a hail claim and sometimes it doesn't. We document what the roof shows either way. When damage is legitimate, a thorough report makes it hard to dispute. When it isn't, we say so.
Who we work with
We work with owners, property managers, and carriers, adjusters and attorneys on hail claims, through forensic roof consulting, commercial roof assessments, large-loss consulting and the appraisal and umpire process. We don't do public adjusting or give legal advice; when a claim needs one, we refer to a highly experienced public adjuster licensed in most states or to trusted large-loss attorneys. We take any size of roof in Texas and Oklahoma, and large-loss work in other states, including Colorado.
When a modified bitumen roof needs repair or replacement after the claim, our sister company handles modified bitumen roofing in North Texas.
General information only, not legal or coverage advice.