Roof Blistering: Causes, Repair & Prevention
Roof blistering is caused by moisture or gases trapped inside shingle layers that expand when heated by the sun, creating raised bubbles on the shingle surface. The three main causes are manufacturing defects that trap moisture during production, installation over damp decking, and poor attic ventilation that causes excessive heat buildup. Small closed blisters are cosmetic, but popped blisters expose the asphalt mat and accelerate roof deterioration.
In Myrtle Beach, roof blistering is more common and more damaging than in cooler climates. Our summer temperatures push attic temperatures above 150 degrees in poorly ventilated spaces, and the intense UV exposure means popped blisters deteriorate the exposed asphalt mat faster than they would in northern states. If your roof has blisters, it is important to understand whether they are a cosmetic issue you can monitor or a structural problem that needs immediate attention.
This guide covers what blisters look like, every cause, when to repair versus replace, how to prevent blistering, and how to handle warranty claims. If you are also seeing other shingle problems like curling or granule loss, read our common roofing problems guide for a complete overview.
In This Guide
What Roof Blistering Looks Like
Roof blisters appear as small raised bumps or bubbles on the surface of asphalt shingles. They can range from the size of a pencil eraser to the size of a quarter. From the ground, they may be difficult to spot, but from the roof surface they are clearly visible as raised areas that feel soft or spongy when pressed.
Stages of Blistering
- Stage 1: Closed blisters — Small raised bumps with the granule surface intact. The blister is sealed and not actively damaging the shingle. This is cosmetic only.
- Stage 2: Expanded blisters — The blisters have grown larger as trapped moisture continues to expand during hot weather. Granules may begin to loosen on the raised surface.
- Stage 3: Popped blisters — The blister has burst, creating a crater-like opening that exposes the dark asphalt layer underneath. Granules are missing from the popped area. This is where real damage begins because UV and water now have direct access.
- Stage 4: Deteriorated blisters — Popped blisters that have been exposed to the elements for months or years. The asphalt around the blister has cracked, dried out, and may have begun to leak. The shingle is at end of life in the blistered area.
Causes of Roof Blistering
1. Manufacturing Defects
The most common cause of blistering is moisture that was trapped between the layers of the shingle during the manufacturing process. Asphalt shingles are made by saturating a fiberglass mat with asphalt and then pressing granules into the surface. If moisture is present during any step of this process, it becomes trapped within the shingle and will expand when heated.
2. Poor Attic Ventilation
Inadequate attic ventilation allows heat to build up against the underside of the roof deck. In Myrtle Beach, attic temperatures in a poorly ventilated space can exceed 160 degrees in summer. This extreme heat bakes the shingles from below while the sun bakes them from above, dramatically increasing the pressure of any trapped moisture or gases. Proper ventilation keeps the attic closer to outside ambient temperature, reducing the temperature differential and the expansion forces that create blisters. See our soffit ventilation guide for more details.
3. Installation on Damp Surfaces
When shingles are installed on damp or wet decking, the moisture trapped between the shingle and the deck creates blistering as it evaporates upward through the shingle in the heat. Professional roofers should never install shingles on wet surfaces, but rushed installations (especially after storms when demand is high) sometimes skip this step.
4. Improper Storage Before Installation
Shingle bundles that are stored improperly (exposed to rain, stacked on wet ground, or left in direct sun for extended periods before installation) can absorb moisture that later causes blistering. Bundles should be stored flat, covered, and off the ground.
5. Multiple Shingle Layers
Installing new shingles over existing ones (layover or re-roof) traps heat between the layers and can promote blistering in both the old and new shingle layers. The trapped layer gets hotter because heat cannot dissipate through the layer above it.
Blistering vs Hail Damage: How to Tell the Difference
This distinction matters enormously for insurance claims. Hail damage is covered by insurance. Blistering is typically not (unless caused by a manufacturing defect covered by warranty).
| Feature | Blistering | Hail Damage |
|---|---|---|
| Shape | Raised bubbles (convex) | Circular dents (concave) |
| Granule condition | Intact until blister pops | Displaced on impact |
| Size variation | Random sizes | Uniform (matching hail size) |
| Pattern | Random placement | Random but affects all exposed surfaces |
| Other surfaces | Only on shingles | Also on gutters, vents, siding |
| Insurance coverage | Usually not covered | Covered |
How Serious Is Roof Blistering?
| Severity | Description | Action |
|---|---|---|
| Minor | A few small closed blisters on scattered shingles | Monitor annually; no action needed |
| Moderate | Multiple blisters, some popped, in one area | Inspect ventilation; replace affected shingles if popped |
| Severe | Widespread blistering across multiple areas, many popped | Fix ventilation; consider full replacement; check warranty |
Repair Options and Costs
Option 1: Monitor (Closed Blisters)
If blisters are small, closed, and not widespread, the best approach is annual monitoring. Check during your regular roof inspection to see if blisters are growing, multiplying, or popping open. No cost beyond normal inspection.
Option 2: Spot Replacement (Popped Blisters in Small Area)
Replace individual shingles with popped blisters. This costs $200 to $500 for a small area and prevents the exposed asphalt from deteriorating further. This is appropriate when the rest of the roof is in good condition.
Option 3: Ventilation Fix + Spot Repair
If poor ventilation is the underlying cause, fix the ventilation first ($500 to $1,500 for ridge vent and soffit improvements), then replace any damaged shingles. This addresses the root cause and prevents future blistering.
Option 4: Full Roof Replacement (Severe, Widespread)
When blistering is severe and widespread, especially if combined with other age-related issues like curling, granule loss, or cracking, a full roof replacement is the most cost-effective solution. This runs $8,000 to $25,000 depending on roof size and materials.
Preventing Roof Blistering
- Ensure proper attic ventilation — This is the most important prevention measure. Balanced intake (soffit vents) and exhaust (ridge vent) keep attic temperatures closer to outside ambient, reducing the heat that causes trapped moisture to expand. Target 1 square foot of net free ventilation per 150 square feet of attic floor.
- Choose quality shingles — Reputable manufacturers (GAF, Owens Corning, CertainTeed) have better quality control that minimizes manufacturing moisture. Avoid bargain shingle brands.
- Never install on wet surfaces — Ensure decking is completely dry before installation. After rain, wait at least 24 hours for the deck to dry.
- Store shingles properly — Keep bundles covered, off the ground, and out of direct sun before installation.
- Avoid installing over existing layers — A tear-off and fresh install eliminates the trapped heat issue caused by multiple layers.
- Hire experienced installers — Proper nailing, alignment, and installation technique reduce the chance of trapped air and moisture. Choose a licensed roofing contractor with manufacturer certification.
Warranty Coverage for Blistering
Whether blistering is covered by the manufacturer warranty depends on the cause:
- Manufacturing defect — Usually covered. You need to prove the blistering is a defect, not an environmental or installation issue. A certified roofing inspector can provide this assessment.
- Poor ventilation — Usually not covered. Most warranties require adequate ventilation as a condition of coverage. If the warranty is denied due to ventilation, fixing the ventilation may prevent further damage even though it does not restore warranty coverage for existing blisters.
- Installation error — May be covered by the installer's workmanship warranty (separate from the manufacturer warranty). Check your installation contract.
To file a warranty claim, you will need the original purchase receipt, installation date, contractor information, and documentation of the blistering (photos and dates). The manufacturer will typically send an inspector to evaluate the claim.
Frequently Asked Questions
What causes blistering on a roof?
Blistering is caused by moisture or gases trapped inside shingle layers that expand when heated. The three main causes are manufacturing defects, poor attic ventilation causing excessive heat buildup, and installation on damp surfaces. Myrtle Beach's extreme summer heat makes blistering worse.
Is roof blistering serious?
Small closed blisters are cosmetic and not serious. Popped blisters expose the asphalt mat to UV and water, accelerating deterioration. Widespread blistering indicates a ventilation problem or manufacturing defect that should be addressed. In Myrtle Beach, popped blisters deteriorate faster due to intense UV exposure.
How do you fix blistering shingles?
For closed blisters, monitor annually. For popped blisters, replace the affected shingles ($200 to $500 for a small area). For widespread blistering, fix the ventilation first ($500 to $1,500), then assess whether partial or full replacement is needed.
Is blistering covered by the shingle warranty?
Manufacturing defects are usually covered. Blistering from poor ventilation or installation errors is usually not. Most warranties require proof of adequate ventilation. Keep installation records and ventilation documentation.
How do you tell the difference between blistering and hail damage?
Blisters are raised bubbles with intact granules until they pop. Hail creates circular dents that displace granules on impact. Hail also damages other surfaces (gutters, vents, siding) while blistering only affects shingles. This distinction matters because hail damage is insured and blistering typically is not.
Can roof blistering be prevented?
Yes. Ensure proper attic ventilation, choose quality shingles from reputable manufacturers, never install on wet decking, store bundles properly, and avoid layering new shingles over old ones. In Myrtle Beach, adequate ventilation is the single most important factor.
Get a Free Roof Inspection in Myrtle Beach
Noticing blisters on your shingles? WeatherShield Roofing provides free inspections that determine the cause and severity of blistering. We will tell you whether you need monitoring, spot repairs, ventilation improvement, or full replacement — and help you navigate warranty claims if applicable.
We are GAF Certified contractors (SC License #124773) with 82 five-star Google reviews, serving Myrtle Beach homeowners since 2022. Honest assessments, no pressure.