Blisters and bubbles on a built-up roof (BUR) are common issues that concern many property owners and facility managers. These raised areas on the roof surface usually signal underlying problems that can affect the roof’s integrity. Identifying the causes and knowing how to address them promptly can prevent costly repairs and extend the lifespan of the roof.
| Aspect | Description |
|---|---|
| Definition | Raised areas (blisters/bubbles) on roof surface from moisture or trapped air |
| Common Causes | Trapped moisture, heat buildup, poor installation, deteriorated roof materials |
| Potential Risks | Water infiltration, membrane damage, structural weakening |
| Detection Methods | Visual inspection, infrared thermography, moisture meters |
| Repair Options | Patching, roofing material replacement, improving ventilation |
What Are Blisters and Bubbles on a Built-Up Roof?
Blisters and bubbles appear as raised, dome-like sections forming on the top layers of a built-up roof. These formations typically contain air, moisture, or a combination trapped beneath the roofing membrane. A built-up roof consists of multiple layers of bitumen alternated with reinforcing fabrics, capped by a protective layer to shield it from the elements.
These blisters emerge when trapped moisture or air expands due to heat, pushing the roofing layers upward. They are often visible as small or large bubbles and can vary in firmness.
Key Reasons Blisters and Bubbles Form on Built-Up Roofs
1. Moisture Entrapment During Installation
One of the most frequent causes is moisture trapped in the insulation or roofing materials during installation. If the materials are not fully dry or work is done under high humidity conditions, water vapor can become sealed within the layers. When the sun heats the roof throughout the day, this moisture expands, causing the roof membrane to blister.
2. Poor Roof Ventilation
Inadequate roof ventilation leads to heat and moisture buildup under the roofing membrane. Without proper airflow, internal humidity levels rise and become trapped, encouraging blister formation as the trapped air expands in higher temperatures.
3. Thermal Expansion and Contraction
Repeated cycles of heating and cooling cause roofing materials to expand and contract. Over time, this thermal movement can weaken the bond between layers, allowing vapor pockets or air to get trapped and form blisters.
4. Deterioration of Roofing Materials
Older built-up roofs may begin to degrade due to UV exposure, aging materials, or mechanical damage. Such deterioration can cause the roofing membrane to become less flexible and more prone to blister formation.
Why Do Blisters and Bubbles on Built-Up Roofs Matter?
Blisters are not merely cosmetic issues; they indicate potential weaknesses in the roof structure that can lead to leaks and water damage. When a blister bursts, water can penetrate the roofing layers, causing rot, mold, or structural damage to the underlying deck. This compromises the roof’s effectiveness in protecting the building and may shorten its service life.
Detecting and Assessing Blisters on Built-Up Roofs
Visual Inspection
Regular roof inspections can identify blistering early. Look for raised bubbles or cracks in the roofing membrane, especially after hot days or heavy rains.
Infrared Thermography
This technology detects temperature variations caused by moisture under the roof surface. Wet or trapped water areas show different thermal signatures than dry ones, helping pinpoint blister-heavy zones.
Moisture Meters and Core Sampling
These methods can verify the presence of moisture trapped beneath the membrane. Core sampling involves removing a section of the roof to examine the layers directly, providing detailed information about the blister’s cause.
Effective Repair and Prevention Strategies
Patching Small Blisters
For minor blisters, roofing contractors can cut out the affected area, dry it completely, and patch it with new roofing materials. This restores the membrane’s integrity and prevents water infiltration.
Replacing Large Damaged Sections
When blisters cover a significant area or repeatedly appear in the same spots, partial or full roof replacement may be necessary. This approach is more expensive but ensures long-term protection.
Improve Roof Ventilation
Enhancing ventilation reduces heat and moisture buildup, minimizing blister formation. Installing ridge vents or exhaust fans in the attic spaces can substantially improve airflow.
Use Proper Installation Techniques
Ensuring roofing materials are dry and installed under recommended weather conditions helps prevent initial moisture entrapment. Hiring experienced roofing contractors who follow manufacturer guidelines is crucial.
Long-Term Maintenance to Avoid Future Blisters
- Regular Inspections: Schedule inspections twice yearly, particularly after extreme weather.
- Routine Maintenance: Seal cracks, repair damage promptly, and clean debris that trap moisture.
- Upgrade Roofing Materials: Consider newer systems with improved moisture resistance if frequent blistering occurs.
The Role of Roof Warranties and Insurance
Many roofing warranties cover blistering caused by material defects or installation issues but exclude damage from neglect or natural wear. Understanding warranty terms can help property owners know when repairs are covered. Additionally, insurance may cover damage from sudden events but rarely from gradual blistering problems.
Summary
Blisters and bubbles on a built-up roof mainly indicate moisture or air trapped under the membrane, poor ventilation, or deteriorating roofing materials. Early detection and appropriate repairs such as patching or roof replacement can prevent leaks and structural damage. Proper installation, roof maintenance, and ventilation are essential to minimize blister formation, keeping the roof durable and functional over its expected lifespan.