What Is Roof Blistering? Causes, Prevention, Repair

Roof blistering is a common yet often misunderstood issue that affects various types of commercial and residential roofing systems. Whether you have an asphalt shingle roof, a built-up roof, or a single-ply system, understanding the phenomenon of roof blistering can be crucial in maintaining the integrity and longevity of your roof. This comprehensive guide aims to shed light on what roof blistering is, what causes it, how to distinguish it from similar conditions like hail damage, and most importantly, how to prevent and address this issue.

Table of Contents

• What Is a Roof Blister?
• Causes of Roof Blistering
• The Impact of Roof Blistering
• Prevention of Roof Blistering
• How to Respond to Roof Blisters

What Is a Roof Blister?

Roof blistering refers to raised areas or bubbles on the surface of a roofing material. These bubbles or blisters often appear to be filled with air or water, giving them a puffed appearance. Blistering can occur on a variety of roofing materials, including asphalt shingles, built-up roofs (BURs), modified bitumen roofs, single-ply roofs, as well as spray foam roofs and elastomeric coatings.

On flat roofs, blisters are almost always caused by poor installation. On asphalt shingles, blisters are usually caused by and inadequate ventilation. These blisters can range in size from as small as a dime to as large as several feet across. They are often spherical but can also take on irregular shapes, depending on the underlying cause and the type of roofing material.

It's important to note that the appearance of blistering can vary depending on the type of roofing material. On asphalt shingles, blisters may appear as small dark spots where the granules have been pushed away. On a single-ply membrane, blisters can look like raised air or water-filled pockets. On foam roofs with elastomeric coatings, blisters may appear as swollen, discolored areas that have detached from the roof substrate.

On most commercial roofs, blisters are often simply a cosmetic problem. However, on elastomeric coatings and spray foam roofs, they can quickly create serious problems water ingress. Water intrusion can then lead to further problems, such as mold growth and structural damage to the building.

Causes of Roof Blistering

Poor installation is one of the most common causes of roof blistering. It often results from inadequate or rushed workmanship during the roof installation process, leading to trapped air or moisture within the roofing layers.

In foam and elastomeric coated roofs, poor installation often takes the form of insufficient preparation of the roof substrate, resulting in poor adhesion of the foam or coating. If there is dust, debris, or moisture on the substrate when the foam or coating is applied, pockets of air or water may become trapped, leading to blister formation as the roof heats up and cools down.

Blistering in Asphalt Shingles

Asphalt shingles are susceptible to blistering, especially when poor manufacturing or installation combines with other adverse conditions, such as poor ventilation in the attic or high rooftop temperatures. When the shingles heat up, any trapped moisture or air within the shingle can expand and push up the shingle's surface, forming a blister.

Proper roof and attic ventilation play a significant role in preventing roof blistering in asphalt shingles. When ventilation is inadequate, heat can build up in the attic. This heats up the shingles, which can lead to the the formation of blisters.

Blistering vs Hail Damage

Popped asphalt shingle blisters and hail damage may at first glance appear similar, as they both lead to a loss of granules, but there are recognizable differences.

An impact from a hail storm causes loss of granulation, but also embeds some granules in the fiberglass mat. In contrast, popped roof blisters result in an almost total loss of granulation, and will not cause granules to embed themselves in the mat.

Another distinct difference lies in their distribution across the roof. Hail damage is likely the cause if only one slope is impacted.

Telling the difference between the two is not always easy, so if you're unsure, you should reach out to a professional roofer who can properly identify hail damage.

Roof Blistering in Built-up Roofs

Built-up roofs (BURs), consisting of alternating layers of bitumen and reinforcing fabric, can also experience blistering. This often happens when air or moisture becomes trapped between the layers during installation. When the roof heats up, these trapped pockets can expand and cause the bitumen layers to separate, forming blisters. The layers' cumulative thickness in BURs can lead to larger and potentially more damaging blisters.

Roof Blistering in Modified Bitumen Roof Systems

Modified bitumen roofs are less prone to blistering than built-up roofs, but blisters can still occur under certain circumstances. Trapped air or moisture between the modified bitumen membrane and the substrate is often the cause. This is typically due to poor installation, such as not correctly torching the underside of the membrane to ensure full adhesion to the substrate.

Blistering in Single-Ply Roofs

Single-ply roofs, such as those made from TPO, EPDM, or PVC, can develop blisters if air or moisture gets trapped under the membrane during installation. It's essential to ensure the roof substrate is clean and dry before the membrane is installed to prevent blister formation.

Blistering on Elastomeric Coatings and Foam Roofs

As previously mentioned, blisters are common on foam roofs and those with elastomeric coatings if the installation isn't done correctly. It's crucial to ensure the substrate is clean and dry and that the foam or coating is applied evenly and at the correct thickness to prevent blister formation.

In conclusion, while various causes can contribute to roof blistering, they often revolve around issues of poor installation, manufacturing defects, and improper ventilation. By addressing these factors, you can significantly reduce the risk of blistering on your commercial roof.

The Impact of Roof Blistering

On most roofs, blistering is not usually a cause for immediate concern.

Blisters can crack or rupture over time due to weather exposure, foot traffic, or thermal expansion and contraction. This can open a pathway for water ingress into the roof system, leading to damaging leaks and moisture build-up. Additionally, exposed areas are more susceptible to further deterioration, including mold growth and rot, especially in roofs with organic decking, like wood.

Prevention of Roof Blistering

For Commercial Flat Roofs

Proper installation is the best way to prevent blisters on flat roofs. The roofing substrate should be thoroughly cleaned and dried prior to the application of the membrane.

For Asphalt Shingle Roofs

When it comes to asphalt shingles, quality plays a critical role in preventing roof blistering. High-quality roofing materials are designed to withstand the pressures of thermal expansion and contraction, reducing the likelihood of blister formation.

It's also vital to ensure that shingles are installed correctly. Poor installation techniques can lead to roof blisters, regardless of the quality of the shingles. So, hiring experienced and reputable roofing contractors is equally crucial to prevent roof blistering.

Proper roof and attic ventilation is another essential factor in preventing roof blisters. An inadequately ventilated roof can trap heat and moisture, leading to accelerated thermal expansion and contraction of roofing materials and, eventually, blistering.

Here are some key points to consider when addressing roof ventilation:

1. Balance between intake and exhaust: A well-ventilated roof should have a balanced system, with equal amounts of intake at the eaves or soffits and exhaust at or near the roof peak. This ensures smooth airflow from the bottom to the top, effectively removing heat and moisture.

2. Correct calculation of ventilation space: The amount of ventilation needed can vary based on the size and design of your building. Generally, there should be a minimum of 1 square foot of ventilation for every 300 square feet of attic space. A professional roofing contractor can provide a more precise calculation based on your building's specifics.

3. Regular inspection and maintenance: Ventilation systems can become blocked or damaged over time, which could compromise their effectiveness. Regular inspection and maintenance can help ensure your roof ventilation remains in good working condition.

4. Using proper ventilation systems: Depending on the type of your roof, certain types of ventilation systems may be more effective. Ridge vents, soffit vents, gable vents, or a combination of these might be used.

How to Respond to Roof Blisters

The first step to addressing roof blistering is evaluating the severity of the problem. To do this, you'll need to look for some tell-tale signs.

1. Number of blisters: The sheer number of roof blisters can be an indicator of the extent of the issue. A single blister may not necessarily be a cause for concern, but multiple blisters may be a sign that a larger problem is at play.

2. Size of blisters: Size is another important factor. Small blisters may not pose a threat to the roof's integrity in the short term. However, larger blisters, particularly those more than 2 inches in diameter, can pose an immediate threat and require attention.

3. Location of blisters: Blisters located on high foot-traffic areas or near crucial parts of the roof, such as flashings or joints, are particularly problematic. These blisters are more susceptible to rupture, which could lead to more significant damage.

4. Condition of blisters: Blisters that remain intact and are not showing signs of rupture or cracking might not require immediate intervention. However, if blisters are already split or cracked, it's best to consult a professional.

When to Contact a Roofing Professional

Once you've assessed the condition of your roof, you may be wondering when you should get a roof inspection from a professional. Here are some general guidelines:

1. Multiple and large blisters: If you notice multiple large blisters on your roof, especially in high-traffic areas or near critical roof structures, it's time to call a roofing professional. These blisters pose a threat to the integrity of your roof and should be addressed immediately.

2. When preventative measures fail: If you've taken preventative steps such as using high-quality shingles and ensuring proper ventilation, yet blistering persists, a professional roofer should be consulted. Persistent blistering could indicate deeper underlying issues that need to be addressed.

3. If you're unsure: If you're uncertain about the severity of your roof's blistering or how to address it, it's always best to consult with a professional.

Remember, it's crucial not to try to repair roof blisters yourself. Improper repair attempts can lead to further damage. Roofing professionals have the necessary knowledge, skills, and tools to perform a detailed roof inspection and address blistering properly and safely.

Addressing roof blistering promptly and effectively is vital to maintaining the integrity and extending the lifespan of your commercial roof. While the initial signs of blistering may not pose an immediate threat, left unchecked, this issue can lead to serious roof damage, costly repairs, and potentially premature roof replacement. By regularly assessing the state of your roof and contacting a roofing professional when needed, you can ensure the longevity of your building.

If you have further questions, feel free to contact our team here at GIDEON. Whether you need advice on specific roofing systems, recommendations for contractors in your local area, or a free inspection of your roof, we're happy to help you in a free, no-obligation call.