Seasonal

Roof Blisters: What a Desert Summer Left Behind

By Scottsdale Roof Repairs · November 2, 2026 · 8 min read

Roofing advice written for the rest of the country spends November on ice dams. Scottsdale essentially never gets one. What it gets instead is roof blisters and the rest of the heat damage that comes with them: a roof surface that ran past 150°F from May through September, materials that expanded and contracted every single day of it, and sealant that has been baked until it has no stretch left. November, with daytime highs finally in the seventies, is the first comfortable month to go find what that did.

What heat actually does to a roof

Three things, in this order.

It drives off the volatiles. Asphalt shingles, felt underlayment and elastomeric coatings all depend on oils and plasticizers that keep them flexible. Heat cooks them out. That is why 30-pound felt under tile dies at 15 to 25 years here instead of 40, and why an architectural shingle rated for 30 years gets 18 to 22 here.

It cycles the materials. This is thermal cycling, and a tile roof deck in Scottsdale can swing 60°F between three in the afternoon and five in the morning. Every material on the roof grows and shrinks a little every day, at a different rate from the one next to it. Metal moves most, asphalt next, concrete tile least. Over a few thousand cycles that shears fasteners loose, opens seams and pulls sealant away from the thing it was sealing.

It blisters. A blister is a pocket of gas or moisture trapped under a membrane that expands when the surface heats. On shingles it shows as raised bumps that eventually pop and leave a bare spot in the mat. On a foam roof it is a bubble under the coating, sometimes the size of a dinner plate.

Where to look for roof blisters in November

• Shingle blistering. Raised bumps, some popped open with dark asphalt showing where the granules blew off. Scattered blisters on a young roof are a manufacturing or ventilation issue; blisters everywhere on a 15-year roof are age.
• Foam roof blisters. Push gently with a foot at the edge, not the middle. A soft, hollow bubble needs cutting, drying and patching before the next coat. Look too for roof coating splitting along seams and around curbs, which lets water reach the foam underneath.
• Sealant that has gone hard. Around pipe jacks, at chimney counterflashing, on skylight curbs, around HVAC curbs on flat roofs. Good sealant dents under a fingernail. Dead sealant is glassy and cracked, and every one of those cracks is a winter leak waiting on the right storm.
• Cracked or lifted pipe boots. Neoprene boots are among the most heat-vulnerable things on a Scottsdale roof, and they usually last about 8–12 years here.
• Nail pops on shingle roofs. Deck movement backs the nail out; the shingle above it lifts into a little tent. Common on the 1970s roofs around Old Town and in South Scottsdale.
• Ridge and hip mortar cracked on 1980s and 1990s tile roofs, where the mortar and the tile have been moving against each other all summer.
• Metal flashing oil-canning or buckled at long runs, especially valley metal and parapet coping.

Blistering versus the things it gets confused with

Ranges, not quotes. The cost page has the full set.

Why the attic is half the story

A shingle roof cooks from both sides. The sun heats the top; a poorly vented attic holds a bubble of 150°F air against the bottom. In older South Scottsdale houses where the soffit vents have been painted shut or stuffed with insulation, the shingles above them age noticeably faster than the same shingles on a well-vented roof two doors down. If a roof is blistering unevenly, look at what is under the bad areas — a blocked soffit run, a bathroom fan dumping into the attic, a section with no ridge vent.

On tile roofs the mechanism is gentler, because the air gap under the tile vents itself, but the deck still gets hot enough to matter and a sealed attic still ages the felt faster.

What to fix before the winter rain

1. Replace any pipe boot that is cracked or hardened — $300–$500 a visit, and it is the cheapest leak you will ever prevent.
2. Cut out and reseal dead sealant at chimney, wall and skylight flashings, or better, replace caulked details with metal counterflashing that does not depend on sealant.
3. Patch foam blisters and tears now; the recoat window reopens in March.
4. Reset cracked ridge mortar before a January storm drives rain under it.
5. Open the soffit vents you find blocked, and confirm the bath fans exhaust through the roof or a gable, not into the attic.

A November walk-around, step by step

1. Start from the street. Use binoculars on a clear morning, when low sun shows raised spots and lifted edges best.
2. Walk the yard. On a shingle roof, look for loose granules at the downspouts and along the drip line.
3. Look at any flat section you can see safely. Check the coating near parapets, scuppers and HVAC curbs for bubbles and splits.
4. Go into the attic on a cool day. Look at the deck under any blistered area for dark stains, and check that the soffit vents let in light.
5. Write it down. Note what you saw and where, with photos, so a roofer can compare your list with what they find up close.

Leave anything that means walking a tile roof to a roofer. Tile cracks under a heel placed in the wrong spot, and a broken tile lets sun straight onto the felt.

Mistakes that make heat damage worse

• Caulking over cracked sealant. A new bead laid on top of dead sealant fails the next summer. The old material has to come out first.
• Recoating over open blisters. A fresh coat over a bubble seals the moisture in, and the blister comes back bigger.
• Pressure-washing a shingle roof. It can strip the granules that shield the asphalt from UV, which speeds up the aging you were trying to clean off.
• Fixing the shingles but not the attic. If the soffits stay blocked, the next set of shingles cooks just as fast as the last one.
• Waiting for the first winter leak. The cheap fixes above cost far less in November than a ceiling repair after a January storm.

When it is not worth chasing

A shingle roof past 18 with blisters, curl and granule loss together is telling you something the sealant gun will not fix. That is a replacement conversation, and the end-of-life signs post has the full list of tells. A tile roof with dead sealant is a different case entirely — the tile is fine, the details are fixable, and the real question is what the felt underneath looks like. That takes lifting a tile, which is what a roof inspection is for, and November is the month a roofer can do it without standing on a 150°F roof.

Common questions

Are blisters on a new shingle roof a defect?

Not always, but they are worth reporting. Scattered blisters in the first few years usually point to a manufacturing issue or poor attic ventilation rather than age. Photograph them, note the date, and ask the installer and the shingle manufacturer how their warranties treat blistering before the bumps pop and shed granules.

Can a blistered foam roof be patched?

Usually, yes. A roofer cuts out the blister, lets the foam dry, fills it with new foam and coats over the patch. The repair holds well as long as the cause of the trapped moisture is found, and it is best done before the next full recoat so the patch is sealed under the new coating.

When is the best time to look for heat damage?

November and early December. The roof surface has cooled enough for a roofer to walk it safely and take their time, the summer's damage is all there to see, and there is still time to fix the small items before the winter rains arrive.

Does attic heat cause shingles to blister?

It contributes. A poorly vented attic holds very hot air against the underside of the deck, so the shingles cook from both sides and age faster than the same shingles on a well-vented roof. Uneven blistering over one section often traces back to blocked soffit vents or a missing ridge vent above that area.