Blistering Shingles: Causes, Warranty Questions, and When It Matters

Shingle blisters are raised bubbles in the asphalt surface that can pop and leave small pits where the granules used to be. Before deciding who to call, check the soft metal on the roof and gutters for dents. Dents support a hail explanation and make your insurer the first call; blistering with no dents makes the shingle manufacturer’s warranty the first place to ask, where the wording decides whether blistering is covered and sets a notice deadline. Neither check is a diagnosis: a roofer’s assessment and the documents decide the route. When you find both, or cannot tell which caused the marks, notify both in writing on the same day so neither deadline runs out.

That check is the first sort, because the two problems can look alike from the ground and go to different payers.

What a Shingle Blister Looks Like, Raised and Popped

A raised blister is a small, rounded bump in the shingle surface, covered with granules like the rest of the shingle. Blisters can be scattered or clustered, and they are easier to see in low, raking light. Look from the ground with binoculars or a zoom lens in early morning or late afternoon, when the bumps cast small shadows; there is no need to climb to identify them.

A popped blister is what remains after the bump breaks open. The granule-covered cap comes off and leaves a small crater with dark asphalt at the bottom and a slightly raised rim around it. From a distance, a slope with many popped blisters looks speckled with dark dots.

This page is about asphalt shingles. Flat roofs blister too, but a membrane blister is a different problem with different repairs; see flat roof repair for membranes, blisters and seams.

Why Shingles Blister

What follows is the general mechanism, not a manufacturer’s statement about any product.

A blister forms when something trapped inside the asphalt layer expands and pushes the surface up. The trapped material can be moisture or gas held in the asphalt, and heat is the trigger: the sun heats the shingle from above, and a hot attic can heat it from below through the deck. When the trapped material expands faster than it can escape, the surface lifts into a bubble. Later heating cycles can enlarge the bubble until the cap breaks.

That points to two places to look. The first is the product and how it was made, which is a manufacturer question. The second is heat and moisture coming from the attic side, which is a ventilation question that can affect any shingle. Neither cause makes blisters automatically a defect or automatically harmless.

Blister or Hail Hit? A Fast Way to Tell

Hail and popped blisters both leave dark spots where granules are missing. The surrounding evidence tells them apart.

The metal check is the one you can do from the ground. Gutters and downspouts are visible without a ladder, and dents on roof vents can show up in binoculars. If you find dents and a storm date, treat it as possible hail damage; see how hail marks show on shingles and soft metal.

The route matters because both manufacturer documents quoted next exclude hail from warranty coverage. GAF’s impact resistance brochure states that “hail damage is not covered under the limited warranty,” and Owens Corning’s Duration Series impact resistance data sheet, dated January 2026, says hail damage “is specifically excluded from coverage under the terms of its warranty.” Hail is an insurance question.

A roof can show both. If you find blisters on one slope and dents plus fresh marks after a storm on another, document them separately, with their own photos and locations, so the insurer and the manufacturer each see the evidence that applies to them.

When Blistering Starts to Matter for the Roof

A raised blister that has not popped still has its granules, so the asphalt under it stays covered; while the cap holds, the change is mostly in how the shingle looks.

A popped blister is different. The pit exposes asphalt to the sun, and exposed asphalt ages faster than asphalt under granules. A few pits on a roof are a small, local loss. Many pits spread across the slopes add up to the same thing as widespread granule loss, and HUD’s Residential Rehabilitation Inspection Guide says asphalt shingles that lose their granules and start to curl should be replaced. For how to read granule loss in general, see shingle granule loss.

Age changes the reading. Widespread popped blisters on a roof only a few years old are an early-failure question worth putting in front of the manufacturer while the warranty is fresh. The same pattern on a roof near the end of its expected life is part of the wear that leads to replacement planning.

Watch three things over time: whether blisters are popping, whether the pits are spreading to new areas, and whether the shingles around them are starting to curl; what each curl shape means helps you read that change. Photograph the same spots each season.

Warranty Claim Logic for Blistered Shingles

A manufacturer warranty covers only what its text says it covers. As the National Roofing Contractors Association’s bulletin on roof system warranties puts it, a manufacturer warranty may promise to repair only leaks “that result from specific causes specified in the warranty.” Whether blistering qualifies depends on your warranty’s wording, so read the coverage and exclusion sections of your own document, and if neither mentions blisters, ask the manufacturer in writing how it classifies them.

Notice deadlines are part of the warranty. As one example, the GAF Shingle and Accessory Limited Warranty, form RESWT160L-0426 for GAF products installed after January 1, 2025, requires you to “notify GAF about any claim within 30 days after you notice a problem.” Other manufacturers set their own terms, so find the deadline in yours as soon as you see blisters.

Build the evidence packet before you file:

• Close-up photos of raised and popped blisters, zoomed from the ground or taken by a roofer with a coin in the frame for scale.
• Wider photos showing where they are on each slope.
• The shingle product name and color, from the invoice, the warranty registration or a bundle wrapper.
• The installation date and the installer’s name.
• Attic photos and notes on ventilation, because a manufacturer may ask about attic conditions.
• The date you first noticed the blisters.

Do not coat or treat the shingles before you file. The Asphalt Roofing Manufacturers Association’s page on aftermarket coatings and rejuvenators, dated July 24, 2026, cautions that a coating or rejuvenator applied after installation may affect how the shingles are classified for fire and impact and how well they resist algae. Ask the manufacturer before applying anything. For the filing steps themselves, see how roof warranties work and how to file.

If the manufacturer points to hail and the insurer points to a manufacturing cause, ask each one for its decision and the clause it relies on in writing. Two written answers that contradict each other give you something specific to dispute; a phone conversation does not.

Manufacturer, Insurer, or Neither?

The metal check sorts the likely route; a roofer’s written assessment of the shingle marks confirms it.

If you find dents in soft metal and can match them to a storm date, report the storm to your insurer. If the shingle marks still look like blisters rather than hail hits, notify the manufacturer as well within its deadline, and document the dents and the shingle marks together.

If you find blisters with no dents or storm evidence, and the roof is within its warranty period, start with the manufacturer. Check the notice deadline in your warranty today, assemble the evidence packet, and file in writing; the warranty’s wording, not the absence of dents, decides whether blistering is covered.

If the roof is past its warranty and there is no hail evidence, the likely route is neither: monitor with seasonal photos and have a roofer look when you see pits spreading or curling begin. Any of the three is easier to support with photos taken before the next season; for what a professional inspection should document, see the findings and photos a roof report should include.

This guide is general information for U.S. homeowners, not legal, insurance, tax, or engineering advice. Codes, laws, and policy terms vary by location and change over time; confirm details with your local building department, your insurer, or a licensed professional.

Sources

• GAF Impact Resistance brochure, GAF
• Duration Series Shingles: Impact Resistance Testing and Classification, Owens Corning
• Residential Rehabilitation Inspection Guide, U.S. Department of Housing and Urban Development
• Roof System Warranties (Consumer Advisory Bulletin Issue 1), National Roofing Contractors Association
• GAF Shingle and Accessory Limited Warranty, GAF
• Application of Coatings or Rejuvenators on Asphalt Shingles After Installation, Asphalt Roofing Manufacturers Association