Roofers call them “blisters.” They usually occur during the first couple of years after roof installation, and are caused by excessive heat under the shingles due to poor ventilation of the attic, which is a common problem in Florida. The heat expands any volatile gasses or moisture trapped in the layers of asphalt during manufacture, which try to escape and form tiny raised blisters in the roof surface. Eventually each blister pops, knocking off the granules above it, then the blister recedes back in place to become the pitted spots you see in the roof shingles. 

 
   Extensive blistering is rare, but could lead to a shortened lifespan of the roof due to the missing areas of granules if widespread across roof. Blistering should not be confused with hail damage, which makes a shallow bowl-shaped indention in the roof with the granules still mostly intact in the area of damage.

   Also, older shingle roofs lose granules in larger areas without clearly defined edges as a natural part of aging. Shown below is an older roof with both granule loss and circled spots of hail damage.

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Here’s links to a collection of our other blog posts about SHINGLE ROOFS:

• Why is granule loss a problem for an asphalt shingle roof? 

• What causes roof shingles to curl up at corners?  

• Why is premature curl of roof shingles a problem?

• What would cause a new asphalt shingle roof to have loose tab adhesion (sealant strips)?

• Can I put a new asphalt shingle roof over an existing shingle roof on a manufactured/mobile home?  

• How can I tell if a roof has more than one layer of shingles? 

• What is the life expectancy of an asbestos cement shingle roof?  

• Does a roof with multiple layers of shingles last longer? 

• Why is a popped nail in a shingle roof a problem? How do I fix it?

• What are the dark lines running parallel to shingles on my roof?

• What is the average lifespan of an architectural (dimensional) shingle roof? 

• What is the average lifespan of a regular (3-tab) shingle roof?

• What does "lack of tab adhesion" in an asphalt shingle roof mean?

• What is the minimum pitch/slope of an asphalt shingle roof?

• What's the difference between an "architectural" and a regular shingle roof? 

• Why is an asphalt shingle roof difficult to inspect when wet right after it has rained?

• How can I tell if an asphalt shingle roof manufacturer's warranty rating is 20 years, 30 years, or more?

    Visit our ROOF AND ATTIC page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.