Small blisters on a commercial roof are a common concern, especially on built-up roofing (BUR) and modified bitumen systems. While not every blister requires immediate repair, they should never be ignored without a professional inspection. Some blisters remain stable for years with routine monitoring, while others grow, rupture, and lead to leaks, insulation damage, and costly roof repairs.
The key is determining whether the blister is cosmetic or a sign of an underlying roofing problem.
What Is a Roof Blister?
A roof blister is a raised bubble that forms when air, moisture, or volatile gases become trapped between layers of roofing material. As temperatures rise, the trapped material expands, causing the roofing membrane to lift away from the layer beneath it.
Blisters can develop in:
- Built-up roofing (BUR)
- Modified bitumen roofs
- Some asphalt-based commercial roofing systems
Single-ply membranes such as TPO, PVC, and EPDM are less likely to develop traditional blisters, although localized membrane separation can occur for other reasons.
Can Small Blisters Be Left Alone?
In many cases, small, intact blisters that are stable and not located in high-traffic areas can be monitored rather than repaired immediately.
A roofing contractor may recommend observation if the blister:
- Remains tightly sealed
- Shows no signs of cracking
- Has not increased in size
- Does not trap standing water
- Is not located near seams, flashing, or roof penetrations
- Is not causing leaks inside the building
Simply cutting open every small blister is not considered best practice because unnecessary repairs can create new entry points for water if performed improperly.
When Does a Blister Require Repair?
A blister should be repaired when it begins affecting the roof’s waterproofing performance or structural integrity.
Warning signs include:
- The blister continues to grow.
- The membrane becomes soft or spongy.
- Cracks develop in the surface.
- The blister ruptures.
- Water enters beneath the membrane.
- Multiple blisters begin appearing across the roof.
- Interior leaks develop.
Once a blister opens, rainwater can enter the roofing system and saturate insulation, significantly increasing repair costs.
What Causes Roof Blisters?
Several conditions contribute to blister formation, including:
- Moisture trapped during roof installation
- Poor adhesion between roofing layers
- Wet insulation beneath the membrane
- Inadequate ventilation during installation
- High thermal expansion caused by repeated heating and cooling cycles
- Aging roofing materials
Understanding the underlying cause is just as important as repairing the visible blister. Otherwise, new blisters may continue to develop.
What Happens If Blisters Are Ignored?
Although some small blisters remain harmless for years, others gradually worsen.
Ignoring deteriorating blisters can result in:
- Membrane splitting
- Water infiltration
- Wet insulation
- Reduced thermal performance
- Mold growth
- Deck corrosion
- Larger repair areas
- Shortened roof lifespan
The longer moisture remains inside the roofing assembly, the greater the risk of hidden structural damage.
How Roofing Professionals Evaluate Blisters
Experienced commercial roofing contractors examine several factors before recommending repairs.
They evaluate:
- Blister size
- Number of blisters
- Location on the roof
- Whether moisture is present
- Roof age
- Membrane condition
- Existing leaks
- Manufacturer recommendations
Moisture scans or infrared roof inspections are often used to determine whether water has entered beneath the membrane before deciding on repairs.
Repair vs. Monitoring
Not every blister requires immediate removal.
Monitoring may be appropriate when:
- The blister is small.
- The membrane remains intact.
- No leaks are present.
- The blister has remained unchanged.
Repair is generally recommended when:
- The blister is growing.
- Surface cracks appear.
- Water infiltration is suspected.
- Roof traffic could damage the blister.
- The blister threatens nearby seams or flashing.
Routine inspections allow roofing professionals to monitor changes over time and intervene before significant damage occurs.
Preventing Future Blisters
The best prevention begins with proper roof installation and ongoing maintenance.
Preventive measures include:
- Installing roofing materials under proper weather conditions
- Keeping insulation dry during installation
- Following manufacturer installation specifications
- Performing regular commercial roof inspections
- Repairing small defects promptly
- Maintaining proper drainage to prevent moisture intrusion
Quality workmanship significantly reduces the likelihood of blister formation throughout the roof’s service life.
Shieldline Roofing’s Expert Opinion
Small, stable blisters don’t always require immediate repair, particularly when the membrane remains intact and the roof isn’t leaking. We recommend documenting and monitoring them during routine inspections, while repairing any blister that is growing, cracked, punctured, or associated with moisture.
Our Key Insights
Not every blister indicates active water intrusion, but puncturing a blister without confirming the cause can make the problem worse by creating a new leak point. A professional inspection can determine whether the blister is cosmetic, caused by trapped moisture, or evidence of a larger roofing-system problem.
The Bottom Line
Small roof blisters do not always require immediate repair, but they should never be dismissed without professional evaluation. Some remain stable and only need periodic monitoring, while others indicate trapped moisture or membrane failure that can quickly develop into expensive leaks.
For commercial property owners, the safest approach is scheduling routine roof inspections so developing blisters can be evaluated early. At Shieldline Roofing, our experienced team assesses blister severity, identifies underlying causes, and recommends the most cost-effective solution to protect your commercial roof and maximize its service life. Learn More
