Evaluating Roof Damage Potential By Material

Over the past week, damaging storms have hammered the Denver Metro and areas in the upper Midwest.  Night after night, the weather is relentless: flash flood warnings, heavy rains, giant hail, flickering power, and constant rumbling from massive thunderstorm cells.  Then the real flooding begins: the flood of claims to the insurance industry for wind damage, hail damage, flooding, and other damages.  How do we wade through the claims?  Advocates for owners are pointing out every ding and dent in a 30-year-old gutter.  They are peeling up shingles, running chalk over roof vents and window frames, looking for any potential damage to include in the claim.   As forensic experts, we are often called to independently evaluate these damages to determine causation, extent, and repair options.


Steep-sloped roofs are common on residential properties, with asphalt shingles being the most popular covering.  The following are the likely types of roofing materials for steep-slope roofing found in the area as well as their potential risk for damage:

•  Heavyweight laminate fiberglass-mat asphalt shingles- These shingles typically can handle hail from 1 to 1-1/2 inches without significant loss of serviceability.

Above: Hail impact damage to laminated asphalt shingles.

• Metal roofing – Hail can affect the appearance of metal roofing; however, lower gauge metal will not be as affected as higher gauge.  The effect of hail impacts is typically minor to severe denting, which is a cosmetic issue and generally does not affect the performance or expected lifespan of the roof.

• Lightweight three-tab fiberglass-mat asphalt shingles- These shingles can be more susceptible to damage from hail, particularly if the shingles are installed over an old layer of roofing.  This is due to the thinner mat and less bitumen surrounding the mat.

• Three-tab organic-mat shingles- These shingles can be a claims nightmare for adjusters.  Many of the organic shingles produced in the 1990’s and early 2000’s were part of a class action lawsuit due to accelerated weathering issues.  These shingles are susceptible to weather cracking/tearing, granule loss, deformation from absorption of water, blistering, and etc.  Distinguishing manufacturing defects and accelerated weathering from hail impact damage takes requires a diligent analysis from an experienced observer.


Low-sloped roofing is more common in commercial applications.  The following is a general overview of low-slope roof types as well as their potential risk for damage (this list is far from inclusive of all types and information):


•  Smooth surfaced – Smooth-surfaced built-up roofs can be damaged by hail and flying debris due to the lack of granules or aggregate protection.  However, the damage is usually visible and repairable

•  Granular surfaced – Granular-surfaced built-up roofs are susceptible to impact damage mainly from the loss of granules.  Such damage can typically be repaired without full scale removal.

•  Aggregate surfaced – Aggregate-surfaced built-up roofs are the least susceptible BUR to impact damage.

Above: Aggregate surface BUR (and ballasted single-ply roofs) are very resistant to impact damage.

Note:  The three roof types listed above can all sustain damage from hail and windblown debris.  If there is a question about damage, a sample of a strike location can be evaluated in our laboratory by solvent extraction of reinforcements.



Polyvinyl Chloride (PVC) – PVC membranes are the most susceptible single-ply membrane to hail impact damage, particularly in a re-cover situation.  Modern PVC’s are less prone to impact damage than the first generation non-reinforced PVC’s.  Reinforced PVCs and improved formulations have brought PVC’s a long way.  Not all PVCs are formulated the same, and plasticizers intended to make the membrane flexible migrate out over time, causing embrittlement.  Most PVC manufacturers use a plasticizer with a high molecular weight to slow this process.  All PVC roofs, particularly aged PVC roofs, should be carefully investigated after a hail or wind event.  (PVC membranes are typically white with the texture of the scrim prominent through the weathering surface)

Thermoplastic Olefin (TPO) – TPO has physical properties similar to PVC and are also susceptible to damage from hail and windblown debris.  According to TPO manufacturers, it does perform similar to PVC’s in a hail event.  TPO does not have plasticizers that migrate out, so they should perform the same until the end of their service life.  (TPO membranes are typically white with a smooth surface)

Above: Hail impact damage to single-ply PVC roof.


Ethylene Propylene Diene Monomer (EPDM) –  EPDM roof membrane is the least susceptible membrane to hail impact damage.  Studies have shown a fairly consistent resistance to hail of up to 3 inches in diameter.

• Chlorosulfinated polyethylene (CSPE)  –  CSPE is most recognized by the trade name Hypalon.  CSPE is actually a thermoplastic that becomes a thermoset as it cures in the field.  CSPE is susceptible to damage from hail and wind-blown debris. (CSPE membranes are white and look like a PVC, but lichen or algae growth can be seen on the surface of the membrane, particularly near the seams)

Note:  Fastening patterns, substrates, and ballast can all play a part in the likelihood of impact damage to a single-ply membrane.  Damage to single-ply membranes can be very difficult to identify.  Impact marks that are not visible on the surface may be visible when the back side of the membrane is closely examined.  If collateral damage is identified near the roof system, a thorough investigation of the membrane should be performed.

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