The short answer
How Heat Creates Blisters
Heat waves push roof surface temperatures well above the air temperature. On dark shingles, the surface can get hot enough to soften the asphalt. When moisture or air gets trapped under that softened layer, it expands and pushes the roof material upward into a blister.
Blisters often show up where the roof has poor ventilation or where the decking was damp during installation. Older roofs with worn surface granules are more vulnerable, because the protective layer has thinned. You may notice small bubbles first, and they can grow over repeated hot days.
Signs of Blistering on Your Roof
Look for raised bumps or bubbles on the roof surface, often a few inches across. They may appear darker or lighter than the surrounding shingles. Blisters can crack open, letting water into the layers below, which can lead to leaks and water damage inside your home.
Check after a heat wave, especially on south- and west-facing slopes that get the most sun. Also inspect around vents, chimneys, and skylights, where the roof structure changes. If you see blisters, avoid walking on them, as they can break and worsen the damage.
- Raised bumps or bubbles on the roof surface
- Cracks or splits in the blister area
- Granules or coating flaking off around the bump
- Dark or discolored patches that feel soft to the touch
- Water stains on ceilings or walls inside your home
- Mold or mildew odor in the attic after a hot day
What Causes Trapped Moisture
Moisture can get trapped under the roof surface from a few sources. Rain or snowmelt can seep through small cracks and sit under the shingles. Humidity from the attic can also rise into the roof deck, especially if ventilation is poor.
When heat hits that trapped moisture, it turns to vapor and expands. That pressure pushes the roof material outward, creating a blister. If the roof was installed over damp wood or wet insulation, the problem may appear within the first few hot seasons.
How to Protect Your Roof
You can reduce blistering by keeping your roof well-ventilated and ensuring attic airflow is clear. Trim tree branches that block air movement near the roof. Check for and seal any small cracks or nail pops that might let moisture in.
After a heat wave, inspect for blisters. If you find them, have a roofing professional look at the affected areas. They can determine whether the blister is just cosmetic or if water has already entered the roof layers.
- Keep attic vents and soffit vents clear of debris
- Seal small cracks and gaps around flashing and pipes
- Trim overhanging tree branches to improve airflow
- Check for blisters after several days of extreme heat
- Avoid walking on blistered areas to prevent breaking them
- Have a roofer assess any blisters you find
When to Call a Roofing Pro
If you spot blisters, it's wise to have a roofing professional examine them. They can tell if the blister is just on the surface or if it goes deeper into the roof structure. Catching it early can prevent water from reaching the decking and insulation.
Heat waves are part of summer in many regions, so checking your roof after hot spells is a good habit. If you notice blisters, water stains, or attic moisture, contact a local roofer for an inspection. They can advise on repairs or replacement if needed.
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Call Now (479) 370-1500Frequently asked questions
Do blisters always cause roof leaks?
Not always. A blister that remains intact may not leak right away, but it weakens the roof's surface. If the blister cracks, water can get in. It's wise to have a roofer inspect any blister to see if it's at risk of leaking.
Can I fix a roof blister myself?
Small surface blisters might be sealed with roofing cement or patch compound, but it's tricky to get it right. If the blister is large or the roof is steep, a professional should handle it. Walking on a hot roof can be dangerous, and improper repairs can make it worse.
Will roof blisters go away on their own?
Blisters rarely disappear on their own. They may flatten in cooler weather, but the trapped moisture remains. Over time, the blister can grow and crack. It's better to have it inspected and repaired rather than waiting for it to cause a leak.