Asphalt shingle
It is one of the most widely used roofing covers in North America because it has a relatively inexpensive up-front cost and is fairly simple to install.
Types of granules tested have included mica, oyster shells, slate, dolomite, fly-ash, silica and clay.
[6] In 1926 the Asphalt Shingle and Research Institute with the National Bureau of Standards tested 22 types of experimental felts and found no significant differences in performance.
In the 1950s self-sealing and manually applied adhesives began to be used to help prevent wind damage to shingle roofs.
Later generations of shingles constructed using fiberglass in place of asbestos provided acceptable durability and fireproofing.
[8] In 1996, a partnership between members of the U.S. property insurance industry, the Institute of Business and Home Safety, and the Underwriter's Laboratory (UL) was established to create an impact resistance classification system for roofing materials.
Subsequently, insurers offered discounted premiums for policies on structures using shingles that carried the highest impact classification (class 4).
Both are made in a similar manner, with an asphalt-saturated base covered on one or both sides with asphalt or modified-asphalt, the exposed surface impregnated with slate, schist, quartz, vitrified brick, stone,[6] or ceramic granules, and the under-side treated with sand, talc or mica to prevent shingles from sticking to one-another before use.
The top surface granules block ultra-violet light, which causes the shingles to deteriorate, provides some physical protection of the asphalt core, and provides color – lighter shades preferred for their heat reflectivity in sunny climates, darker in cooler ones for their absorption.
The early wood material-based versions were very durable and hard to tear, an important quality before self-sealing materials were added to the underside of shingles to bond them to the layer beneath.
Widespread hurricane damage in Florida during the 1990s prompted the industry to adhere to a 1700-gram tear value on finished asphalt shingles.
While more expensive to install, they come with longer manufacturer's warranties, sometimes up to 50 years - typically prorated, as virtually all asphalt shingle roofs are replaced before such an expiration could be reached.
Asphalt shingles have varying qualities which help them survive wind, hail, or fire damage and discoloration.
Thermal shock can damage shingles, when the ambient temperature changes dramatically within a very short period of time.
[citation needed] "Experiments...have noted that the greatest cause of asphalt shingle aging is thermal loading.
Eventually the loss of the heavy oils causes the fibers to shrink, exposing the nail heads under the shingle flaps.
Cycles of wet and dry environmental conditions, as well as organic growths such as algae and foliose lichen and woody debris which remains on the shingles, will cause premature deterioration through both chemical and physical processes.
[16] Post-consumer RAS have fewer appealing properties for recycling, primarily because the asphalt cement component in shingles naturally hardens during its service life, resulting in higher stiffness, melting point, and susceptibility to fatigue cracking.
[17][19] Post-consumer RAS also require additional processing, such as the removal of nails and other metal waste through the use of a magnetic sieve.
[21] The primary reason restrictions on the use of RAS exist is the rare presence of asbestos in asphalt shingles manufactured before the early 1980s.
