Asphalt shingles are an American invention by Henry Reynolds of Grand Rapids, Michigan.[2] They were first used in 1903, in general use in parts of the United States by 1911 and by 1939 11 million squares (100 million square meters) of shingles were being produced.[3] A U.S. National Board of Fire Underwriters campaign to eliminate the use of wood shingles on roofs was a contributing factor in the growth in popularity of asphalt shingles during the 1920s.[4] The forerunner of these shingles was first developed in 1893 and called asphalt prepared roofing, which was similar to asphalt roll roofing without the surface granules.[5] In 1897 slate granules were added to the surface to make the material more durable. Types of granules tested have included mica, oyster shells, slate, dolomite, fly-ash, silica and clay. In 1901 this material was first cut into strips for use as one-tab and multi-tab shingles.
All shingles were organic at first with the base material, called felt, being primarily cotton rag until the 1920s when cotton rag became more expensive and alternative materials were used. Other organic materials used as the felt included wool, jute or manila, and wood pulp.[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. The design standard was for the self-sealing strips of adhesive to be fully adhered after sixteen hours at 140 ยฐF (60 ยฐC). Also in the 1950s testing on the use of 3โ4-inch (19 mm) staples rather than roofing nails was carried out showing they could perform as well as nails but with six staples compared with four nails.[3] In 1960 fiberglass mat bases were introduced with limited success; the lighter, more flexible fiberglass shingles proved to be more susceptible to wind damage particularly at freezing temperatures. Later generations of shingles constructed using fiberglass in place of asbestos provided acceptable durability and fireproofing.[7] Also in the 1960s research into hail damage found that it occurs when hail reaches a size larger than 1.5 inches (38 mm).
The Asphalt Roofing Manufacturers Association (ARMA) formed the High Wind Task Force in 1990 to continue research to improve shingle wind resistance.[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. The system, known as UL 2218, established a national standard for impact resistance. Subsequently, insurers offered discounted premiums for policies on structures using shingles that carried the highest impact classification (class 4). In 1998, Texas Insurance Commissioner Elton Bomer mandated that Texas provide premium discounts to policyholders that installed class 4 roofs.[9]
Types
Asphalt shingles on a home in Avalon, New Jersey
Two types of base materials are used to make asphalt shingles, organic and fiberglass. 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 โ lighter shades preferred for their heat reflectivity in sunny climates, darker in cooler ones for their absorption. Some shingles have copper or other biocides added to the surface to help prevent algae growth. Self-sealing strips are standard on the underside of shingles to provide resistance to lifting in high winds. This material is typically limestone or fly-ash-modified resins, or polymer-modified bitumen. American Society of Civil Engineers ASTM D7158 is the standard most United States residential building codes use as their wind resistance standard for most discontinuous, steep-slope roof coverings (including asphalt shingles) with the following class ratings: Class D โ Passed at basic wind speeds up to and including 90 mph (140 km/h); Class G โ Passed at basic wind speeds up to and including 120 mph (190 km/h); and Class H โ Passed at basic wind speeds up to and including 150 mph (240 km/h). An additive known as styrene-butadiene-styrene (SBS), sometimes called modified or rubberized asphalt, is sometimes added to the asphalt mixture to make shingles more pliable, resistant to thermal cracking, and more resistant to damage from hail impacts. Some manufacturers use a fabric backing known as a scrim on the back side of shingles to make them more impact resistant. Most insurance companies offer discounts to homeowners for using Class 4 impact rated shingles.