The lifespan of asphalt shingles depends highly upon the environment. Shingles in cooler climates such as the northern United States seem to last longer than those installed in the warmer climates. Studies have shown that the average lifespan for a 20 year shingle in Phoenix, Arizona is around 14 years. In Minneapolis, Minnesota the lifespan was 19.5 years. And in Reading, Pennsylvania, the lifespan was 20.8 years.

From this data it seems obvious that the hotter the environment is, the shorter the service life of the shingles. One thing that's very damaging to shingles is Thermal Shock. Thermal Shock is what roofing materials experience when the ambient temperature changes dramatically within a very short period of time - usually 24 hours. For example, in Yreka, California, the temperatures during a summer day can often reach 100 degrees and at night, they'll often drop below 50, sometimes as low as 40. Roofing materials are unable to expand and contract to accommodate such a dramatic temperature change in such a short period of time so cracks and splits in the materials start occurring. Water can then enter the materials and damage them further in two ways. One is the damage water does to asphalt materials in general. It's not that water hurts asphalt, but algae and fungus do and the continuous presence of water will permit algae and fungus to grow on asphalt materials. Another way water damages is the freeze-thaw cycle. In the cold months, water will get into the cracks and then freeze at night. Water expands as it freezes so the more this occurs, the bigger the cracks or splits become. This is why most roofing contractors and consultants are such big advocates of sloped roofs. The better the roof sheds water, the less problems it will usually experience.

Still another factor affecting asphalt shingle roofs is attic ventilation. Proper roof ventilation has been known to extend the service life of a roof.

• Strip Shingles - these asphalt shingles are approximately three times as long as they are wide. Manufactured in both standard and metric dimensions, strip shingles are distinguished by the number of cutouts or tabs that they have. The most common type of strip shingle is the "three-tab" shingle. Different textural and lighting/shadowing effects can be achieved with strip shingles depending on the number, shape and alignment of the cutouts.

• Laminated Shingles - these special shingles contain more than one layer of tabs to create extra thickness. They are also referred to as three-dimensional or architectural shingles because they create visual depth on a roof and impart a custom look. Laminated shingles continue to be a favorite among builders, roofing contractors and homebuyers.

• Interlocking Shingles - as the name suggests, interlocking asphalt shingles are individual shingles that mechanically fasten to each other, and are used to provide greater wind resistance. They come in various shapes and sizes providing a wide range of design possibilities.

• Large Format Shingles -generally rectangular or hexagonal in shape, these shingles do not utilize cutouts or tabs.

• Product Performance - Asphalt shingles perform well in extreme temperatures and in areas where wind, water, and ice are prevalent.

• Affordability  -The efficient, high-volume production and relatively low application cost of asphalt shingles provide consumers with an overall value that’s tough for other roofing materials to match, especially in terms of comparable life expectancy.

• Low Maintenance - Asphalt shingles, when properly chosen and applied, require little or no regular upkeep, and are easily repaired if damaged.

• Ease of Application - Asphalt shingles are considered to be the easiest of all standard roofing materials to apply. In addition, the flexibility and strength of asphalt shingles supports their application on a wide variety of roof designs.

• Fire and Wind Resistance - Asphalt shingles are manufactured to resist external fire and flammability standards, and carry Class A, B or C fire ratings, with Class A providing the greatest fire resistance. These fire ratings are defined by nationally recognized standards and tested by independent testing agencies. In addition, many asphalt shingles carrying a "wind resistance" label indicate that they have been manufactured and tested to demonstrate acceptable resistance in high-wind locations.

Sooner or later, every roof needs to be replaced, usually due to the long-term effects of weathering. If a residential roof is more than 20 years old, it is a prime candidate for reroofing. To determine if you need a new roof:

• On the ground, walk around your home with binoculars and inspect your roof for cracked, curled or missing shingles, as well as any excessive loss of the protective mineral granules. DO NOT CLIMB ON THE ROOF; walking on the roof is dangerous and can damage your roof.

• In your attic, take a flashlight and look at the underside of the roof deck and rafters for any stains or wet spots indicating water leaks.

Asphalt shingles can often be applied directly over existing roofs without the necessity of tearing off the old roof. However, new shingles can not be properly applied over hard or brittle materials, uneven surfaces for nailing or roof decks with warped, rotted or unsound support that should first be replaced or repaired.

Some local ordinances forbid reroofing over two or more layers of shingles. If a home already has been shingled several times, it is important to first determine if the roof deck can support another layer of shingles before undertaking any re-roofing project.

In addition to asphalt shingles, asphalt roll products are used for residential roofing applications (primarily for underlayments and flashings). There are four basic types of roll roofing materials, each tailored for use in certain job requirements:

• Smooth Surfaced Roll Roofing - Also termed coated felt, this smooth-surfaced roll roofing is covered with ground talc or mica. It is used primarily as flashing to seal the roof at intersections and protrusions, and for providing extra deck protection at the roof’s eaves and valleys.

• Saturated Felt - This asphalt-impregnated, organic-based felt is used as an underlayment between the roof deck and the roofing material. Saturated felt is produced in a variety of weights.

• Specialty-Eaves Flashings - This self-adhering, polymer-modified bituminous sheet material is designed for special flashing applications along roof eaves and in other areas. It is used particularly in regions where ice dams and water backups are common.

• Mineral-Surfaced Roll Roofing - This type of roll roofing is used alone as a primary roof covering, most frequently on small or secondary-use buildings such as supply buildings, barns, garden sheds, etc. The top surface of the roll is imbedded with mineral granules.