Hail Damage on a Foam Roof in Columbia, MD: What Breaks Under the Coating

On a foam or single-ply roof the hail damage is almost never where you are looking. The coating cracks, the membrane fractures in its top ply, the board underneath takes the hit — and the surface above it all reads fine from six feet up.

Nearly everything written about hail is written about asphalt shingles, and those criteria do not transfer. A flat roof fails by a different mechanism, is assessed with different tools, and is far more often repairable in place.

What hail does to a spray foam roof

An SPF roof is closed-cell rigid foam sprayed in place under an elastomeric coating, because the foam will not survive UV on its own. Two materials, and the coating goes first.

SPFA-139, the Spray Polyurethane Foam Alliance's guideline for repairing hail and wind-driven damage, describes the signature plainly: gouges, cracks and punctures, with hail-induced coating cracks often forming patterns shaped like crow's feet or semicircles. Nothing else up there cracks in a star.

Depending on stone size, shape and hardness, the foam underneath may be dented, cracked or gouged, at depths SPFA puts at one-eighth to three-quarters of an inch — mostly cosmetic on the day, against a system usually an inch or more thick.

What they start is not. SPFA-139 notes hail damage is occasionally not discovered for months or years, and that by then repairs may be more extensive from UV degradation and moisture intrusion through the breached coating. The trade explanation for the spread — widely taught, not a published standard — is that water entering a breach runs along the interface between coating and foam rather than down through it, so the wet area creeps sideways from a hole nobody found.

The flat-roof version of the hit count

For shingles there is no published threshold, and the circulating hits-per-square figures trace to carrier guidelines rather than any standard. For SPF there is a table. SPFA-139 classifies damage by severity crossed with extent per 100 square feet, in four degrees:

Degree	Size and severity	Recommended repair
Light	1/2 in diameter, or less than 1/8 in deep	Caulk and coat; recoat if many
Moderate	1/2 to 3/4 in diameter, or less than 1/4 in deep	Coat or caulk; recoat to seal cracks
Heavy	3/4 to 1-1/2 in diameter, or 1/4 to 1/2 in deep	Remove damaged foam; or scarify 1/2 in, refoam, coat
Severe	1-1/2 in or larger, or 1/2 in deep and over	Remove damaged foam; or scarify 3/4 in, refoam, coat

Extent is counted as fewer than 10 or more than 20 defects per 100 square feet, with anything in between left to judgment against the manufacturer's recommendations.

Read what it is. A repair-method table, not a replace-or-not threshold — every row ends in a repair. SPFA-139's stated objective is that research indicates this class of impact damage typically does not cause an SPF roof to leak and can usually be repaired economically without replacement — a strange thing to be sold a tear-off against.

Why a foam roof is the one system repaired in place

A shingle bruise cannot be reversed. A dented foam roof can be ground back and rebuilt from the dent up — scarify a half inch or three-quarters, refoam, recoat — and what comes back is a continuous system rather than a patch, for a fraction of a replacement. Recoating is the cycle a foam roof was designed around anyway.

That cuts both ways: because the repair is cheap relative to a replacement, a full-replacement scope on a lightly dented foam roof earns the question of what is being replaced.

Hail damage on a TPO roof, and why EPDM behaves differently

Single-ply is where most low-slope hail arguments happen, and the two families do not fail alike.

TPO and PVC, both thermoplastics, fracture. Impact testing produces a concentric circular or star-shaped fracture in the top ply — findable close up, invisible from any distance, easy to walk past on a dirty roof.

EPDM, a thermoset rubber, mostly does not. Damage shows as indentations in the boards underneath plus small discrete tears that are hard to see with the naked eye. Field evidence backs it: in RICOWI's investigation of the 11 April 2016 North Texas hailstorm, three EPDM inspections in hail between 1.0 and 3.0 inches documented no punctures or fractures.

The same investigation is the reason not to over-read that. Of 27 single-ply roofs inspected, seven had severe damage, and two unballasted thermoplastic membranes were significantly damaged by hail under two inches. Attachment matters too: a mechanically attached membrane spans between fastener rows on whatever board is under it, where a fully adhered one is backed continuously.

What is underneath decides more than the membrane does

The result that reframes the whole subject comes from testing bituminous roofs, and applies to every low-slope system.

ASTM D3746 drops a free-falling steel missile calibrated to the impact energy of a 2-inch hailstone. In work presented to IIBEC in 2022 by Stephen L. Patterson, RRC, PE, samples built over insulation had fractures in the felts at every impact area. Samples without insulation had none. Same missile, same membrane, opposite outcome — a rigid substrate backs the membrane, a compressible one lets it deform until the reinforcement tears. The substrate is not a detail under the roof; it is the variable.

Which is why single-ply claims lean on the insulation — and why the thermal argument attached to them needs care. Haag tested dented polyiso, 2 to 4 inches thick, some with half-inch gypsum coverboard, and found the dents had no measurable effect on R-value — every reading inside the heat-flow meter's own ±2 percent accuracy, at concentrations well above the 2 to 7 dents per 100 square feet seen in the field. A dented board is not automatically a degraded board. The case for replacing it is that it no longer supports the membrane, or that it is wet.

Modified bitumen and built-up: closer to shingles, different thresholds

Mod bit and BUR behave most like a shingle roof, having granules and a reinforcing mat and failing the same two ways: granules displaced enough to expose bitumen, and fracture of the reinforcement underneath. The difference is that no thumb settles it.

ASTM D3746 rates impact areas 0 for no damage, 2 for dents or indentations only, 4 for any cracks or splits — and, as Patterson notes, the protocol sets no pass or fail rating, so interpretation is left to the reader. Crushed interply bitumen and fractured felts are the signatures, and both are found by cutting a sample out and opening it.

Age loads the dice: FM Global's Data Sheet 1-34 flags deteriorating felts and alligatored surfaces as especially prone to hail damage, and a brittle roof fails at stone sizes a sound one shrugs off.

Infrared and moisture scanning, the tool shingles do not have

Because low-slope insulation holds water where a shingle roof sheds it, a flat roof can be surveyed for moisture. A shingle roof has no equivalent.

ASTM C1153 covers locating wet insulation with infrared imaging. It works at night: the roof takes on solar heat all day and radiates it back after dark, and wet insulation holds it longer, so it glows. ASTM D7954 does the same with an electrical impedance scanner, and its scope explicitly includes spray-applied polyurethane foam.

Two limits. C1153 requires the anomalies it finds to be verified by cutting cores — the scan locates, the cut confirms. And neither dates anything: a scan showing wet insulation proves wet insulation, not that hail put it there in the storm being claimed. Its real value is as the baseline the next storm is measured against.

FM ratings: the standard that actually applies to a flat roof

Shingles are graded by UL 2218 and rigid coverings by FM 4473, both explained alongside the inspection method. What gets specified on a low-slope building is FM's assembly rating — deck, insulation, cover board and membrane rated together, not a product alone.

Data Sheet 1-34 lists the minimum impact energy each rating must survive: 8 ft-lb for moderate hail, 14 for severe, 24 for Class 4 and 53 for very severe. It also puts hail impact energy at 1 ft-lb for a 1-inch stone, 8 at 1.75 inches, 14 at 2 inches and 35 at 2.5 inches, at average density.

Line those up and the ratings stop being marketing: SH is about a 2-inch stone, VSH above a 2.5-inch one. FM draws its hazard areas the same way: moderate to 1.75 inches on a 15-year mean recurrence interval, severe to 2 inches, very severe above.

The credential question on a flat roof in Maryland

Foam and single-ply sit awkwardly across the trade categories. A coating applicator, a residential roofer and a commercial roofer are not always the same credential, and a flat roof is where that seam shows — so find out what, if anything, your state asks of the person going up the ladder.

The credential is an MHIC license from the Home Improvement Commission, and the number to know is that there is no dollar threshold at all - any home improvement work needs one, whatever it costs. Your deposit is capped at one third, and no money may be taken before you sign. The guaranty fund pays up to thirty thousand dollars per claimant, but only against a licensed contractor, and an unlicensed one cannot enforce the contract against you.

The recoat offer, read against Maryland law

The flat-roof version of the free-roof pitch is a recoat: we will coat the whole roof, the carrier pays, your deductible is handled. Note the arithmetic in it: a coating pass costs a fraction of a replacement, so the gap between what is billed and what is done is where the offer lives.

Maryland treats this as a fraudulent insurance act, and grades it a felony once three hundred dollars is involved - up to ten thousand dollars and fifteen years, with the fine mandatory and not subject to suspension. Three limits matter, though: it reaches weather damage only, applies only where payment comes from policy proceeds, and requires intent to defraud the insurer. Unlike some states, Maryland does not separately ban advertising the practice.

Bottom line

Foam cracks in crow's feet, and SPFA's table ends in a repair on every row. TPO and PVC fracture in the top ply; EPDM hides its damage in the boards below. What is underneath decides the outcome. Get the degree, the count per hundred square feet and a cut sample, and treat a scope that reaches replacement without those three as one written before the roof was looked at.

A low-slope roof needs the core cut open, not just a walk over it. Columbia MD Roof Pros writes that up in Columbia and Howard County — degree, count per hundred square feet, cut samples — as part of storm damage restoration, with documented roof inspections and roof replacement if the boards underneath have gone. Call (866) 814-0634 and we will say plainly when a recoat is all it needs.