Cracking Through Reinforcement
Depending upon the style of shingle, the normal weathering characteristics described earlier may be a sign of more serious problems. For example, cracks across a typical three-tab shingle may be a sign of a weak reinforcement. This type of cracking threatens the waterproofing integrity of the roof and needs to be addressed immediately.
For the overlayed-style shingle, on the other hand, cracks that are restricted to the un-reinforced decorative built-up are the result of normal weathering and do not compromise the long-term performance of the roof system.
Granule Loss Exposing Asphalt
Large areas of granule loss that expose the underlying asphalt place the shingle at risk of premature failure because UV rays can now get to the asphalt layer.
In situations in which hail has knocked off large areas of granules, you can expect the life of your shingles to be appreciably reduced due to the effects of ultraviolet radiation from the sun. Shingles with open blister in which the asphalt becomes visible are also at greater risk for premature failure.