How Do You Tell Hail Damage From a Tear, a Backed-Out Nail, or Foot Traffic?

Four conditions get mistaken for hail on an asphalt roof in Oklahoma, and there is one published test that separates all four at once: direction. A hailstone dents the shingle inward and fractures the mat underneath, leaving a spot you can feel through the shingle. Marring from a tool or a boot pushes asphalt and granules outward into a ridge around the edge of the mark. A backed out nail is not an impact at all. Arrowhead Roofing has inspected northeast Oklahoma roofs since 1987, and publishing the ways an inspection can be wrong is the only honest way to write about the ways it is right.

Note: this is a general guide only. It describes what the published assessment literature says an inspector looks at. It is not a coverage opinion, and what a policy pays for is a matter for your carrier and your policy.

Here are the four, side by side, with the tell for each.

The Short Answer

Hail leaves a bruise. Everything else leaves something you can distinguish from a bruise once you know what a bruise is.

The engineering literature has been consistent on this since the 1990s. A hail bruise is an indentation with a fracture in the mat that feels soft under a thumb, like a bruise in an apple. That is the operative description, and the reason it matters is that it is tactile rather than visual. The fracture is detectable on the underside of the shingle. Granule loss on its own is not damage and never has been.

So the inspection is not really a search for round marks. It is a search for fractured mat, with the round marks as the thing that tells you where to put your hands.

How an Inspection Establishes That Hail Fell At All

Before anybody argues about a shingle, there is a step that settles a lot of arguments on its own, and it happens off the roof.

Soft metals record the storm. Air conditioner fins, electrical boxes, gutters, downspouts, vent caps, mailboxes and fence caps all take the same hail the roof does, and they are made of materials that dent at sizes that do nothing to a shingle. Where a hailstone strikes an oxidized or grimy metal surface it cleans the surface film away and leaves a spatter mark. Those marks are not damage. They are evidence, and they are the reason a competent inspection walks the property before it climbs.

What the soft metals establish is whether hail fell, roughly what size it was, and which direction it came from. All three of those constrain what can honestly be claimed about the roof afterwards.

The Test Square

The published field method is more structured than most people expect, and it is worth describing because it is what separates an inspection from a walk around.

The assessment protocol published through the National Roofing Contractors Association calls for test areas examined on each directional slope, because hail arrives at an angle and marks the faces turned into it far more heavily than the faces turned away. A ten foot by ten foot square is the working unit. The protocol also says to site those squares away from tree shaded areas and away from high traffic areas, which is a quiet acknowledgement that both distort the count.

Damaged shingles are then counted per square. What the protocol does not do is publish a universal threshold number. It sets the repair or replace question as an economic comparison rather than a fixed count. Anyone who tells you there is a published number of hits per square that triggers a replacement is repeating an adjusting convention as though it were a standard.

The Four Look-Alikes, One at a Time

Each of these fails at least one part of the hail test, and each fails it in a specific way.

A tear or a mechanical mark

The single most useful sentence in the assessment protocol is about marring, and it applies to tools and to boots equally: marring results in a ridge of bitumen and granules at the perimeter of the mark.

That ridge is the whole thing. A hailstone compresses the shingle downward and fractures the mat below the point of contact. A hammer, a ladder foot or a dropped bundle drags and displaces material sideways, and the displaced material has to go somewhere, so it piles at the edge of the mark. Run a thumb across the boundary and the difference is obvious.

Distribution is the second tell. The literature on fabricated damage notes that deliberate and mechanical marks tend to occur in groups or in lines, and are frequently concentrated in the middle of shingles away from the edges, where a hailstorm has no reason to prefer one part of a shingle over another.

A backed out nail

This one is the easiest of the four, because the research states it flatly. Elevated fasteners occur during installation, either because the nail was not driven flush or because it was driven into a joint between deck boards where it had nothing to hold. And then the sentence that ends the argument: elevated fasteners are not caused by hail striking the roof.

What you see is the shingle above being tented, buckled, or eventually punched through from underneath by the nail head. It is a real defect and it will eventually leak. It is not hail, and writing it up as hail is how a whole report loses credibility.

Foot traffic

Marring from walking has the same signature as marring from a tool, for the same physical reason.

The mechanism, as published: someone walks across the roof on a day when the shingles are hot and pliable, the asphalt at the surface softens to the point where it is pushed aside along with the granules, and it typically forms a ridge on the outside edge of the mark. Walking also removes granules along the bottom edges of shingles, where the exposed lip takes the abrasion.

On a Tulsa roof in July that is not a hypothetical. Surface temperatures on a dark roof here run far above air temperature, and a shingle at that temperature marks under a boot without anybody doing anything wrong.

Thermal splitting

A split is not an impact, and the position of a split gives it away.

The mechanism is a combination of asphalt shrinkage, deck movement and low tensile strength in the mat, and the resulting splits run diagonal and horizontal. The genuinely useful part is where they land. Splits form where a shingle bridges the joints in the underlying course, so they follow the stair step offset pattern created when the roof was installed. That produces a repeating geometry that traces the assembly rather than the weather.

Hail falls randomly. A split that lines up with the joints of the course beneath it did not fall out of a cloud.

Two More Worth Knowing

Neither is on the usual list, and both come up on older roofs here.

Blisters

Blisters form from a combination of poor quality asphalt and heat, and they appear as small bubbles in the shingle surface with a raised patch of granules on top. They are usually a quarter inch across or less, and they are not caused by hail.

There is a complication worth stating, because it is the honest version. A hailstorm too small to do any functional harm can still break the granule crust off a pre-existing blister, leaving a round bare spot that looks a great deal like an impact. That is one of the reasons the tactile check matters more than the visual one. A popped blister has lost asphalt. A hail impact has not.

Ordinary granule loss

The most common false positive of all, and the one with the best evidence behind it.

A ten year field study removed roughly 6, 15, 45 and 70 percent of the granules from test shingles and tracked them. The conclusion was that the small quantity of granules a hailstorm removes does not shorten the life of the roof or affect its water shedding, as long as the impacted areas are not bruised or punctured and remain covered with granules.

There is a colour test that helps in the field. Where granules have flaked off through ordinary weathering, the asphalt underneath has been oxidizing for years and reads grey. Where a hailstone has just knocked granules off, the asphalt underneath is fresh and reads black.

Where the Literature Genuinely Disagrees

One point is contested, and pretending otherwise would be the wrong way to write this page.

Chipped shingle edges. The NRCA assessment protocol says chipped edges do not shorten service life and generally are not included in the count. Haag Engineering’s own white paper says hail caused chips in the butts or edges of shingles can constitute functional damage in some instances. Those are two of the most authoritative sources in the field and they do not agree.

What both agree on is that shingle edges are genuinely vulnerable, because edges at ridges, rakes, eaves and valleys have little or no support underneath them. Which means edge involvement is a real finding worth documenting, and also a finding that two qualified people can weigh differently.

What the Whole Thing Turns On

Every one of these judgements feeds into a single question, and it is not a question about appearance.

Functional damage is defined in the assessment literature as a reduction in the water shedding capability of the roofing, or a reduction in its expected service life. That definition originated with Haag Engineering, was adopted into the protocol published through the NRCA, and was restated in peer reviewed work published by the Insurance Institute for Business and Home Safety in 2025. It is an engineering formulation rather than a legal one, and it is worth attributing rather than presenting as a rule handed down from nowhere.

The practical version: a mark that will not shorten the life of the roof or let water through is a mark, not damage. The inspector’s job is to state accurately what hail did and did not do. Applying the policy to that is the adjuster’s job, and they are different jobs.

Related Questions

What does a genuine hail impact look like, then?

Round, randomly scattered, heavier on the slopes facing the storm, and soft under a thumb. What does hail damage look like on a roof? covers the signature in full, including what it looks like on the soft metals.

Can you tell how long ago it happened?

Sometimes, and less precisely than people want. How can you tell old hail damage from new hail damage? covers what ages a mark and what does not.

How much of this does an adjuster actually look at?

More than most people assume, and in a defined order. What does an adjuster look for on a roof? covers the sequence and what gets recorded.

See Also

The two answers on either side of this one are how much damage it takes before a roof gets replaced, and what the most common local stone size actually does to a shingle.