Consider the conditions a roof must endure. First there is the intense heat of the sun, which scorches the surface of the roof and raises rooftop temperatures 50º – 70ºF above ambient temperature. The sun’s rays are relentless, especially during the early afternoon hours. In addition to heat, the sun is the source of 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 coloured 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 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 160ºF. Now imagine a cold front sweeping through the area, bringing with it the violent thunderstorms that are a common occurrence during the sweltering days of summer. Almost instantaneously, the rooftop temperature drops 60º – 100ºF 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 of the climatic and external variables that can impact the performance of a roof, consider the internal factors that negatively influence the performance of roofing 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 shingles.
As you can see, the roofing environment is a hostile one with many factors influencing the longevity of roofing shingles. The natural aging process begins as soon as the shingles are installed on a roof. Day after day the shingles are exposed to the elements – sun, rain, heat and cold. A roof never has a “good” day.
Asphalt is one of the primary ingredients in roofing shingles. Its purpose is to provide the waterproofing integrity for the roof. Secondarily, the asphalt holds the coloured granules in place and contributes to the overall strength of the shingle. Asphalt, which is derived from petroleum, contains the oils that provide ductility and pliability to the shingles. During the lifetime of the shingles these begin to rise to the surface, where they are washed away by rainwater. In an attempt to restore equilibrium, new oils surface and the washing process continues. Also, the intense heat of the roof oxidizes or hardens the asphalt over time.
Wind is a major threat to a shingle roof system. Shingle sealant, drip edge, the construction of the shingle itself, and using proper fastening techniques are the primary defenses against wind damage.
Heat – A Natural Enemy of Asphalt
Heat, along with ultraviolet light, causes asphalt shingles to age through chemical changes that stiffen the asphalt. Initially, shingles are protected from ultraviolet light by the granules embedded in their surface. As long as the asphalt stays flexible the granules will stay in place. Eventually, however, the shingles become brittle and the granules break loose and gradually wash away.
Excess heat accelerates this aging process, causing the shingles to become prematurely brittle and show all the signs of aging, such as cracking, curling, clawing, and spalling. The aging shingles lose their granules at a faster and faster rate and subject them to even more rapid deterioration from ultraviolet light.
Fortunately, accelerated shingle aging can be slowed by reducing the heat from directly below the roof deck. Proper attic ventilation is the best way to achieve this objective and is a key component of the shingle roof system.