Blistered and Cupped Shingles: What an Inspection Measures

From the ground, a blistered shingle looks like a small bubble, and a cupped one looks like a tab that has curled up at the edges. Neither one is a leak yet. The question an inspector answers is how many shingles are doing it, which slopes they sit on, and whether the sealant strip still holds the tab down. That count decides whether the roof needs a few hand repairs or a longer conversation about replacement.

What a blister is

A blister is a raised spot in the asphalt surface, often the size of a coin or larger, where the shingle has separated slightly from the mat beneath it. Heat, moisture trapped during manufacture or installation, and gas pockets can all push the surface up. Some blisters stay flat for years. Others crack open, and once the surface breaks, the mat underneath loses its protection and granules start to come loose in the same spot. A cracked blister is a repair item, and it belongs on the scope with a photo and a measurement.

What cupping looks like

Cupping is a different problem. The middle of the shingle stays flat while the edges rise, so the tab looks like a shallow bowl. It usually shows up on the sun-facing slopes, where daily heating and cooling push the shingle up and down over many seasons. When the edges lift far enough, wind can get underneath them and tear the tab along the nail line. An inspector checks whether the sealant strip still bonds the tab to the course below by lifting a corner gently, so the shingle is not broken in the process.

Why St. Louis puts stress on the same shingles

Our roofs take heat in summer and freeze and thaw in winter. A sealant strip that bonded well in June can lose some of its grip after several hard freezes, and a tab that was sealed in the morning can lift in the afternoon sun if it was never fully pressed down at install. The south and west slopes take the most sun, so they age faster and show cupping first. The north slope often looks fine from the ground and still has a few tabs that never sealed properly.

Attic ventilation matters here too. A hot attic bakes the underside of the shingles and speeds up the aging of the asphalt from below, which is why the inspector checks the attic while the roof is being walked. Blistering and cupping on a roof with poor airflow may be a symptom of heat, not just a shingle that was wrong from the start.

What the inspector counts

A useful inspection does more than say the shingles look worn. It records the following for each slope:

• How many blisters are present, and how many have cracked open
• How many tabs show cupping, and roughly how far the edges have lifted
• Whether any tabs are unsealed, meaning they lift without resistance
• Whether the sealant strip shows an open gap, a torn strip, or a strip that never bonded
• Whether granules are collecting in the gutters below the affected slope
• Where each affected area sits relative to the ridge, the eave, and the valleys

Each of these becomes a line on the report with a photo. A scale in the photo, such as a tape measure or a folding rule laid beside the shingle, lets you check the measurement later without taking the inspector's word for it.

A few affected shingles versus many

A handful of blistered shingles on one slope is usually a repair. The affected shingles can be replaced individually if the bundle matches and the surrounding shingles are sound enough to hold a new one. Many blistered or cupped shingles across several slopes point to a roof whose shingles are aging together, and that changes the repair question. Replacing individual shingles on a roof where the rest of the field is brittle can damage neighboring shingles during the lift, so the scope should say whether the inspector expects that risk.

Cupping that lifts the tab but leaves the sealant strip intact is a different case from cupping where the strip has torn free. A torn strip means wind has an open path under the tab, and that is where the repair dollars concentrate.

How to read the written scope

Keys documents what the inspector sees, and puts a written scope with photos and measurements in your hands. Read the scope for three things: the number of affected shingles per slope, the photos that show the sealant condition, and a clear statement of what is being recommended. If the scope says cupping on the south slope but does not say how many tabs, ask for the count before you decide anything.

Keep the scope and the photos together with the attic notes and any gutter photos. If the same blistering appears in a later inspection, the earlier record shows whether it is spreading.

Insurance questions on blistered or cupped shingles

Blistering and cupping can come up during a storm claim, and when they do, the rules are strict. Missouri law (RSMo 407.725) forbids a roofing contractor from representing or negotiating a homeowner's insurance claim, and it forbids the contractor from saying anything about paying, waiving, or covering a deductible. Keys can document the shingles, put the written scope in your hands, and attend as the contractor while you deal with your own insurer. The claim decision and any conversation about what the policy pays stay with you and your insurer.

Questions to ask before anyone lifts a tab

1. How many tabs will be checked, and will the count appear on the scope?
2. Will the inspector lift a corner to test the sealant, and how will it be done so the shingle is not broken?
3. Which slopes are expected to show cupping, and why?
4. Does the attic need a check for heat or airflow while the roof is walked?
5. If individual shingles are replaced, will the scope say whether the surrounding shingles are likely to survive the lift?

To set a time for an inspection of blistered or cupped shingles, call Keys Roofing at (314) 220-2333.