Consider the conditions your roof must endure. First there is the intense heat of the sun, which scorches the surface of the roof and raises rooftop temperatures 50-75°F above ambient temperature. The sun's rays are relentless, especially during early afternoon hours. In addition to heat, the sun is the source of the ultraviolet radiation, which has been shown to degrade and accelerate the aging of the asphalt layers of the shingle. If not for the protective layer of the colored granules, roofing shingles would fail very quickly. Other factors such as moisture, pollution and physical effects (roof traffic, hail, snow loads, tree limbs etc.) all contribute to the aging and degradation of your roofing shingles.

Seasonal and weather changes also play a role in the aging of asphalt roofing shingles. For example, consider the common situation in which the roof is bathed in the intense heat of the summer sun. On such a day the rooftop may reach temperatures in excess of 160°F. Now imagine a cold front sweeping through the area, brining with it the violent thunderstorms that are a common occurrence during the sweltering days of summer. Almost instantaneously, the rooftop temperature drops 60-100°F as it's pounded with a summer shower. Thermal shocks such as this cause the roof deck beneath to expand and contract. placing a strain on the shingles. Year after year this process is repeated, resulting in cyclic fatigue of the shingles.

In addition to all the climatic and external variables that can impact the performance of your roof, consider the internal factors that negatively influence the performance of roof shingles. Research has confirmed that an improperly ventilated air space inhibits air movement and under most circumstances increases moisture content in comparison with properly vented attic air spaces. heat shortens the shingles' life and moisture causes deck movement and/or deterioration, which ultimately affects the performance of the shingles.

As you can see, the roofing environment is a hostile one with many factors influencing the longevity of your roofing shingles. The natural aging process begins as soon as the shingles are installed on your roof. Day after day the shingles are exposed to the elements - sun, rain, heat and cold.

Your roof never has a "good" day. 

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