Asphalt Shingle Roofs

Asphalt shingle roofs are installed over plywood or manufactured
wood product sheathing. Typical roof pitches range from 3:12 to 12:12.
The most common defects found in asphalt shingle roofs include the
following:
1. Blistering. Blistering in shingle roofs is caused by a combination of
a loss of granules from the shingles and the penetration of moisture
into the asphalt of the shingle. When blistering occurs, the roof is
at the end of its service life.
2. Buckled shingles. Shingles that have been nailed too tightly can
buckle when they expand in the heat of the sun. Buckles also can
form as the result of damage from foot traffic on the roof. Buckled
shingles is a sign that the roof is approaching the end of its service
life.
3. Cracked shingles. As asphalt shingles age, they lose much of their
flexibility. As a result, cracks can form on the shingle tabs. Cracks
can also form as the result of personnel walking on the roof. Eventually,
the crack will expand and the tab will separate from the
shingle. The formation of cracks in asphalt shingles is an early
warning that the roof is approaching the end of its service life.
4. Curled shingles. Exposure to heat and ultraviolet radiation dries
the asphalt material in the shingles. As the shingles dry they tend
to curl along their edges. Curled shingles is a sign that the roof will
require replacement in the near future.
5. Flashings. The most common defects found in the flashing used
with asphalt shingle roofs include corrosion and separation.
Flashings should be replaced as part of roof replacement programs.
Defective and leaking flashings should be repaired as quickly as
possible.
6. Loss of granules. The granules embedded in the surface of the asphalt
shingles can loosen and be carried away as a result of a breakdown
of the asphalt material from aging. Granule loss is a gradual
process. When the loss is sufficient to result in bare spots in the asphalt
shingle, the roof has reached the end of its service life.

7. Missing tabs. Missing tabs can be the result of aging, wind, or
localized damage to the roof. If the number of missing tabs is minimal,
the damages shingles can be replaced. If a moderate number
of tabs are missing from shingles scattered throughout the roof, it
is a sign that the roof will require replacement in the near future.
8. Rotted underlayment. If an asphalt shingle roof has been leaking
for some time, the plywood or manufactured wood product
underlayment may have rotted. Rotted underlayment is difficult to
detect, but often will appear stained from the underside. It will also
feel soft or spongy when walked on. Rotted and damaged
underlayment requires replacement of all or part of the roof.