How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manfuactured and modular homes
What causes small areas of pitting or pockmarks in an asphalt shingle roof?
Monday, June 17, 2019
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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