How Normal Weathering Affects Your Roof

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 degrees F 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 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. Sudden changes in temperature are called thermal shocks, and can cause the roof deck beneath your shingles to expand and contract, placing a strain on the shingles. Year after year this process is repeated, resulting in cyclic fatigue of the shingles.

Research has confirmed that improperly ventilated air space inhibits air movement and increases moisture content. Heat shortens the shingles' life, and moisture causes deck movement and/or deterioration.

What can I expect my roof to look like as the aging process takes place?

Curling: As the asphalt hardens over time, the granules, which were once securely embedded, begin to break away. Occasionally you may see the colored granules in your gutters. As this hardening advances, the asphalt layers begin to shrink. As the asphalt layer shrinks, it is being countered by the shingle reinforcement, which resists shrinking. We now have a situation in which the top and bottom coatings are shrinking and the reinforcement is remaining stable. As a result, the edges of the shingle may begin to curl over time.

Surface Cracking: Another manifestation of the normal aging process may be the development of surface cracks. As the oils of the asphalt are depleted due to heat, the shingle becomes more brittle, to the point where surface cracking may appear. The stresses created by thermal shock and the movement of the roof deck also increases the likelihood of surface cracking.

Blisters: During the course of natural weathering, small bubble-like raised areas known as blisters may appear on the surface of the shingles. The blisters may be small and pea-sized or as large as a quarter. The blisters may be open, exposing the asphalt, or closed. Blisters frequently result when minimum ventilation requirements are not met.

Staining: Over time, shingles may develop dark brown or black streaks that are sometimes mistaken for soot, dirt, moss or tree droppings. In actuality, the discoloration may be caused by algae growth. Although most roofing systems are susceptible to algae discoloration, it is most readily visible on which or light-colored shingles.

The Life Cycle of a Roofing Shingle

Research indicates that aging begins soon after the shingles are installed and progresses rapidly during the initial curing phase of its life cycle. During this stage, granule loss may occur, small blisters may develop or the shingles may curl slightly at their edges. You may even notice that this curling is more pronounced during cold weather and the shingles may lie flat as temperatures rise. The good news, however, is that after this curing stage, the shingles enter a long period of slow aging, which lasts for the major portion of the shingles' natural life.

During the mid-life period, aging continues at a much slower rate. The cracking or granule loss still occurs but does not increase at a noticeable rate. Only after this long period of mid-life does the aging process begin to accelerate once again as the shingles enter their declining years. It's during this period that homeowners normally think about replacing their roofs.

Facts About Organic and Fiberglass Shingles

Both types of shingles provide years of service. Organic shingles are preferable in colder climates; Fiberglass shingles are preferable in warmer climates.

Fiberglass Shingles:

Resist heat better - no blistering
Require installation of asphalt saturated felt underlayment
Resist curling better than organic shingles
Higher fire resistance rating

Organic Shingles:

Softer - more likely to blister in high temperatures
Usually require heavier weight reinforcement than similar fiberglass shingles
More flexible and tear resistant
Hide roof imperfections better than fiberglass shingles