Roof Blistering: Detect, Reasons, Impacts, and Fixing

Written By Adam Paul - Waterproofing Expert

Roof blistering is the formation of raised bubbles or pockets between roof layers or on the surface. Roof blistering occurs due to poorly installed roofing materials, exposure to extreme temperature shifts, or lack of proper ventilation, rapid temperature fluctuations, aging, and the installation of incompatible roofing components.

Roof blistering can be visible on mostly BUR and modified bitumen roofings in flat roofs. To detect the roof blistering, homeowners need to check raised or bubbled spots on roof shingles, soft or spongy areas on the roof, uneven roof surfaces, and splitting or cracks in the roof area.

Roof blistering damages the roof’s waterproofing membrane, causes leaks, harms insulation, shortens the roof’s lifespan, increases energy bills, and promotes mold and mildew growth inside the home. To prevent these blistering impacts, roof blisters should be fixed in a proper way by following a successful method. In this guide, we have included a blistering fixing guide from our waterproofing experts. To prevent roof blistering, you should install roofing under dry conditions, use high-quality materials, improve roof ventilation, apply adhesives and sealants properly, avoid laying over existing blistered areas, and maintain a proper roof drainage system on the roof.

What Is Roof Blistering?

Roof blistering is the formation of raised bubbles or pockets between roof layers or on the surface. Roof blisterings typically filled with air or moisture and it can be seen on both pitch and slope roof types. Roof blistering occurs mostly in asphalt-based roofing systems, especially built-up roofs (BUR) and modified bitumen roofs. As well as shingle roofs, particularly in hot climates, are also prone to blistering when poor ventilation or moisture presence is involved.

These blisters occur when gas or liquid gets trapped between the roofing membrane or materials and expands due to heat. The trapped pressure weakens the roofing structure, causing visual swelling that compromises both performance and appearance over time.

How to Detect Roof Blistering?

To detect roof blistering, we need to inspect the roof regularly, especially after extreme temperature changes or storms. Most cases begin as minor swelling before evolving into large pockets. We recommend below 5 ways to detect the roof blistering.

Here are five ways to detect roof blistering

Check for raised or bubbled spots on roof shingles or membrane surfaces after sunny days.
Identify soft, spongy areas on the roof that give under light foot pressure.
Discover uneven roof surface textures during routine visual inspections.
Find discoloration or patches on the roof where blisters have ruptured and exposed materials.
Observe splitting or cracking in affected roof areas, especially on aged or sun-damaged sections.

What Are the 7 Reasons for Roof Blistering?

Roof blistering occurs due to poorly installed roofing materials, exposure to extreme temperature shifts, or lack of proper ventilation, rapid temperature fluctuations, aging, and the installation of incompatible roofing components.

Here are the 7 main causes of roof blistering:

Trapped moisture during installation: When water or humidity is sealed within roof layers causes pressure buildup when heated during roofing installations.
Poor roof ventilation: Inadequate airflow in the attic or roof deck leads to heat and humidity accumulation under the roof.
Low-quality roofing materials: Inexpensive or improperly stored roofing products lose bonding integrity under sun exposure.
Improper adhesive application: Uneven or insufficient bonding of roofing materials allows air pockets to form between layers.
Rapid temperature fluctuations: Hot sun and cool rain cause roof materials to expand and contract over time which cause to wekaing the membrane and blistering.
Aging or weathered roof surfaces: Over time, UV rays and rain degrade roofing material surfaces and make them more prone to blistering on shingles over time.
Incompatible roofing components: Mixing different roofing materials without considering chemical or physical compatibility causes separation under stress due to heat and water.

What Are the 7 Impacts of Roof Blistering?

Roof blistering can seriously degrade the structural integrity and performance of your roofing system by compromising the waterproofing membrane, leaking water, damaging the insulations and vapor barrier, decreasing the roof lifespan, increasing the bills, damaging the aesthetic view, and prone to grow mold and mildew in the ceilings.

Here are 7 major impacts of roof blistering:

Compromised waterproofing membrane: Blisters weaken the roof protective layer by making it easier for water to seep through.
Roof leaks and moisture intrusion: Opened blisters become direct channels for rainwater to penetrate the structure.
Insulation damage: Roof blistering damages the roof insulation layer due to water leaking overtime.
Decreased roof lifespan: Frequent blistering accelerates wear and forces premature roof replacement.
Increased energy bills: Damaged roofing fails to insulate properly and making HVAC systems work harder.
Aesthetic degradation: Blisters cause visible bubbling, warping, and discoloration that ruin the roof’s appearance.
Potential mold and mildew growth: Trapped moisture inside the roof system fosters organic growth that spreads indoors.

A roof can be damaged by other roof problems, such as roof alligatoring, ceiling cracks and roof seepage. So you should be aware all of these problems before fix the roof damages.

How to Fix Roof Blistering?

Fixing roof blistering involves a careful process of assessing the damage, removing the affected area, and restoring the integrity of the roof system. At Aqviz, we always recommend addressing blisters early to prevent deeper water intrusion or structural issues.

Here is a step-by-step guide to fix roof blistering:

Inspect the roof surface thoroughly: Identify all blistered areas and note their size, location, and condition pay attention to whether they’re soft, cracked, or leaking.
Cut and remove damaged material: Use a utility knife to carefully cut open the blister without damaging the surrounding membrane or shingle, then remove all loose or deteriorated material inside.
Dry the exposed area completely: Use a heat gun or allow natural drying to remove all trapped moisture before patching, especially in sunny and low-humidity conditions.
Apply roofing cement or adhesive: Spread a uniform layer of roofing cement or compatible adhesive on the cleaned surface to ensure strong bonding with the patch material.
Place and secure the patch: Install a new patch using matching roofing material, pressing it firmly into the adhesive and overlapping the surrounding surface to prevent water entry.
Seal all edges and seams: Apply a layer of roofing sealant or bitumen around the patch to create a watertight barrier against future leaks or blistering.
Allow curing and inspect post-repair: Let the repair cure according to the manufacturer’s instructions, then check for adhesion strength and surface consistency after 24-48 hours.

How to Prevent Roof Blistering?

Preventing roof blistering starts with proper material selection, correct installation, and ongoing roof maintenance. At Aqviz, we’ve learned that most blistering issues can be avoided by addressing moisture control, ventilation, and temperature stress from the very beginning.

Here are the key steps to prevent roof blistering:

Ensure dry installation conditions: Always install roofing materials in dry weather and make sure substrates are completely moisture-free before application.
Use high-quality roofing materials: Choose well-manufactured, UV-resistant, and properly stored shingles or membranes that can handle thermal stress.
Install proper attic and roof ventilation: Promote airflow using ridge vents, soffit vents, or turbine fans to control heat and humidity buildup beneath the roof.
Apply adhesives and sealants correctly: Follow manufacturer instructions on temperature ranges, spread rates, and curing times to avoid trapped air pockets on roof.
Avoid layering over existing blisters: Never install new material over blistered or damaged roofing sections, always repair underlying issues first
Schedule regular roof inspections: Check for early signs of blistering, especially after seasonal weather changes or storms, and address issues promptly.
Maintain proper roof drainage: Clear gutters, downspouts, and scuppers regularly to prevent standing water, which contributes to moisture intrusion and pressure buildup.

Can Roof Waterproofing Stop Blistering?

Yes. Roof waterproofing prevents moisture from entering the roofing layers, which is the main cause of blistering. By sealing the surface and improving water resistance, waterproofing systems reduce the risk of trapped moisture and pressure buildup under heat.

Which Roofing Is Blistering Mostly?

Asphalt-based roofing blisters the most due to heat sensitivity, moisture absorption, and poor ventilation compatibility. These systems are layered and prone to trapping air or water between sheets.

Subtypes of asphalt roofing that blister commonly:

Built-Up Roofing (BUR): Multiple asphalt and felt layers trap moisture easily.
Modified Bitumen Roofing: Heat-applied sheets expand and blister if not properly installed.
Asphalt Shingles: Common in residential roofs, especially in hot climates or poorly ventilated attics.

How Long Can a Roofing Material Withstand Without Blistering?

A well-installed and properly ventilated roof can withstand 15 to 25 years without blistering, depending on material quality, climate conditions, and maintenance. Roofs with premium waterproofing systems and good airflow can even go beyond 30 years blister-free in ideal conditions.

Which Roofing Is Not Blistering?

Roofing systems that resist blistering offer long-term durability, minimal maintenance, and improved energy efficiency. They maintain structural integrity, prevent water damage, and reduce the risk of early roof failure. Choosing blister-resistant roofs also lowers repair costs and enhances the building’s overall lifespan.

Roof types that do not blister easily:

Metal roofing
EPDM (ethylene propylene diene monomer)
PVC membrane roofing
TPO (thermoplastic polyolefin) roofing
Clay tile roofing
Slate roofing
Concrete tile roofing

Which Part of the Roof Is Mostly Blistering?

The parts of a roof most prone to blistering are those exposed to high heat, poor ventilation, or moisture accumulation.

5 Most impacted roof parts.

Roof valleys
Ridge lines
South-facing slopes
Low-slope sections
Around penetrations (vents, chimneys, skylights)

Inspecting these roof parts will help you to troubleshoot the roof problems.

Which Types of Roof Are Mostly Blistering?

Roof geometry plays a big role in blistering potential. From our years of experience, flat and low-pitched roofs are the most vulnerable due to water ponding and heat buildup. These designs offer less drainage and limited airflow beneath the surface.

Roof types that blister the most.

Flat roofs: Flat roofs have a poor drainage system. It leads to standing water and heat retention, which causes roof blistering overtime.
Low-slope roofs: Low slope roofs have a slower water runoff and limited air circulation which cause to trap the water in the roofing membranes.
Shed roofs with minimal pitch: Shed roofs are often exposed to one-sided sun without proper venting, which causes to increase thermal impacts overtime.
Gambrel roofs with poor ventilation: Moisture buildup in upper angles.
Combination roofs with flat sections: Mixed geometries trap moisture at transition points.

You can choose a better roof type among these 9 types of roofs. We have included all about roofs, their functionality, and efficiency in this guide.