Roof membrane blistering is a very common issue in commercial and low-slope roofing systems, often leading to premature wear and potential leaks. While some blisters may seem minor, they can weaken the integrity of your roof over time. Understanding what causes roof blistering and how to fix it can help property owners extend the lifespan of their roofing system and avoid expensive repairs down the line.
What Is Roof Membrane Blistering?
Roof membrane blistering occurs when air, moisture, or gas becomes trapped between the layers of a roofing membrane. Over time, exposure to heat and pressure causes these pockets to expand, leading to visible bubbles or raised areas on the roof’s surface.
Common Types of Roofs Affected by Blistering
- TPO and EPDM Roofing – Single-ply membrane systems can develop blisters due to poor adhesion or moisture infiltration.
- Modified Bitumen Roofing – The layered composition of this material makes it vulnerable to blisters when moisture gets trapped between the plies.
- Built-Up Roofing (BUR) – Older tar-and-gravel roofs often experience blistering due to heat exposure and trapped air pockets.
Blisters may be small and localized or they can spread across large sections of the roof. While minor blisters may not cause immediate damage, larger ones can weaken the membrane, making the roof more susceptible to leaks.
What Causes Roof Membrane Blisters?
Roof blisters form when roofing materials fail to bond properly, allowing air or moisture to become trapped beneath the membrane. Several factors contribute to this issue, such as:
Trapped Moisture During Installation
If a roofing system is installed over a damp substrate or during humid conditions, moisture can become sealed inside the roofing layers. Over time, temperature fluctuations cause the moisture to expand, creating blisters.
Poor Adhesion to the Substrate
A strong bond between the membrane and the roof substrate is essential for long-term performance. If the adhesive is applied incorrectly or exposed to contaminants like dust or debris, it can weaken, leading to blistering.
Thermal Expansion and Contraction
Roofing materials expand and contract with temperature changes. If a roof isn’t installed with enough flexibility or the adhesive cannot accommodate movement, the membrane may lift in areas, forming blisters.
Aging and UV Exposure
Prolonged exposure to sunlight degrades roofing materials over time. UV rays can break down adhesives and cause the membrane to lose its flexibility, increasing the likelihood of blistering.
Blistering often results from a combination of these factors, making it essential to identify the root cause before proceeding with repairs.
Are Roof Membrane Blisters Dangerous?
Not all roof blisters require immediate repairs, but understanding their impact can help determine the right course of action.
When Are Blisters a Cosmetic Issue?
Small, stable blisters that do not change in size or affect the waterproofing of the roof may not need immediate attention. These are often caused by minor adhesion issues and may not impact the roof’s functionality.
When Do Blisters Indicate a Serious Problem?
Blisters that continue to grow or that occur in multiple areas can indicate deeper issues, such as moisture infiltration or poor installation. If the blisters rupture, they can expose the underlying layers to water damage, leading to leaks and structural deterioration.
If a roofing system has extensive blistering, it’s best to consult a professional commercial roofing contractor to assess whether repairs or a full replacement are necessary.
How to Fix Roof Membrane Blistering
The right repair approach depends on the severity of the blistering. A professional inspection can determine whether targeted repairs or a more extensive solution is needed.
Conducting a Roof Inspection
A thorough inspection should identify the number, size, and location of the blisters, as well as any underlying causes such as moisture buildup or adhesive failure.
Patching Small Blisters
For minor blisters that have not ruptured, applying a high-quality adhesive or sealant can help re-bond the membrane to the substrate. This is a cost-effective solution that prevents further separation.
Replacing Affected Sections
When blistering is more widespread, it may be necessary to cut out the affected areas and replace them with new membrane material. This approach ensures the repaired sections are properly bonded to prevent future issues.
Improving Ventilation and Drainage
If moisture buildup is contributing to blistering, improving ventilation and drainage can help prevent recurrence. Choosing the right roofing ventilation is key to regulating airflow and reducing trapped moisture, which helps protect the membrane from premature damage. Proper airflow reduces trapped moisture, while well-maintained drainage systems prevent water from seeping beneath the roofing layers.
Considering a Full Roof Replacement
If a roof has extensive blistering or if previous repairs have failed, a full roof replacement may be the best long-term solution. A new roofing system installed with proper adhesion techniques and moisture control measures will help prevent future blistering.
Addressing roof blistering effectively comes down to understanding its severity and choosing the right repair strategy. Whether it’s a simple patch, improved ventilation, or a full replacement, taking the right steps early can help extend your roof’s lifespan and prevent bigger issues down the road.
How to Prevent Roof Membrane Blistering
Preventative measures can significantly reduce the risk of blistering and prolong the life of a roofing system.
Ensure Proper Installation
Hiring an experienced roofing contractor is one of the most effective ways to prevent blistering. A well-installed roof will have properly applied adhesives, moisture-free materials, and a strong bond to the substrate.
Schedule Regular Roof Inspections
Routine inspections help catch early signs of blistering before they become severe.Commercial roofs, in particular, benefit from regular inspections to catch early signs of blistering. OSHA’s roof inspection guidelines outline safety measures and best practices for maintaining roofing systems.
Choose High-Quality Materials
Investing in durable, high-performance roofing materials can reduce the likelihood of blistering. Modern adhesives and reinforced membranes are designed to withstand temperature fluctuations and environmental exposure.
Taking these steps can help maintain a smooth, well-adhered roofing membrane, reducing the chances of blistering over time.
Keeping Your Roof in Top Condition
Roof membrane blistering is a common but manageable issue. While some blisters may be minor, widespread or growing blisters can compromise the roof’s integrity. Identifying the underlying cause—whether it’s trapped moisture, poor adhesion, or thermal movement—ensures the right repair approach is taken. With proper installation, regular inspections, and proactive maintenance, property owners can prevent blistering and keep their roofs in top condition for years to come.
