What Causes Blisters on Asphalt Shingle Roofs?

One of the most common reasons for service calls among roofing and window companies is asphalt shingle blisters. They may look the same as impact damage from hailstones but they’re entirely different. In this blog, V. Nanfito Roofing & Siding, Inc. discusses what causes asphalt shingle blisters and how the problem can be prevented.

What Causes Asphalt Shingle Blisters?

Asphalt shingles are made of two basic layers: a backing material, which can be made of recycled paper (“organic” shingles) or fiberglass, and an outer layer of granules. The latter is made of crushed minerals that protect the backing material from UV rays. It also contains colored granules, as well as other features that make it algae resistant. During manufacturing, the backing material is soaked in asphalt before being coated with granules. Variations in moisture levels and temperature at the factory may result in moisture getting trapped in the asphalt layer.

Blisters form on the shingles when heat from the sun causes the pockets of moisture to expand. Other heat sources, particularly trapped heat in the attic caused by poor ventilation, can also do the same. This is why roofing and window replacement contractors recommend proper attic ventilation. Trapped heat and moisture in the attic can cause long-term damage to the roof framing, as well as ice dam formation during winter.

How to Prevent Asphalt Shingle Blisters

The good news is that if your asphalt shingle roof was installed within the last ten years, it’s much less likely to form blisters. Manufacturers such as GAF have stringent quality standards, which include testing their products for moisture content. If blisters form on your roof, call your roofing contractor for repairs. Your roofing warranty may have coverage against roofing blisters if it’s a defective product.

While the heat from the sun isn’t preventable—which means blisters during hot days can’t be stopped—there is something you can do about heat from the attic. If your roof seems to be lacking in ventilation, roofing contractors like us offer ridge vent systems from manufacturers like GAF. There should also be enough air intake through the soffits to allow proper air circulation. Large roofs may require active ventilation from exhaust fans.

V. Nanfito Roofing & Siding, Inc. is your leading provider of quality roofing systems and replacement windows. Give us a call at (203) 639-1634 or fill out our contact form to schedule an appointment.