Asphalt shingles

Asphalt shingles are usually made with bitumen from refined petroleum. Roofing felt is coated with asphalt and colored mineral or ceramic granules. These materials are classified by size, shape, weight, color, life expectancy, and fire or wind resistance. Glass fiber-reinforced felts have been the most commonly used asphalt shingles produced since the late 1970s.

History
The first composite roofing was used in New England in the 1840s. These roofs were usually made of a felted or woven fabric that was covered with a tar-like substance like pine tar and sand. Later improvements included saturating the fabric with asphalt and a mixture of materials like talc, sand, or powdered gravel or limestone. The first true composition roofing was credited to the S.M and C.M Warren Company. This roofing was made of coal tar, which was a byproduct of the gas lighting industry, and rolled felt that was saturated with the tar and fine gravel. Roll roofing emerged in the last part of the nineteenth century and became commonplace at the beginning of the twentieth century. Roll roofing was soon replaced by asphalt shingles.

The idea of shaping asphalt roofing into individual shingles is credited to Henry M. Reynolds of Grand Rapids, Michigan in 1903. A roofing contractor and manufacturer, he started cutting stone-surfaced roofing into 8 by 16 inch shingles by hand, with a knife. Adding crushed granules of slate—a 1914 idea from F.C Overby of the Flintkote Company—helped weight such shingles down to the roof. From here a new industry seems to have sprung. A big help was a push by the National Board of Fire Underwriters to eliminate wood shingle roofs, starting around 1911. World War I was a boost too because asphalt shingles made use of non-strategic materials. It was not until about 1915, however, that manufacturers perfected the machinery for roller-die cutting thick roofing into irregular shapes on a continuous production line, thereby opening a cornucopia of asphalt shingle products to the market.

Asphalt shingles were initially cut into 8 by 12 ½ inch pieces that were meant to imitate the wood shingles. Originally, the surfacing materials were natural materials like black or green slate. Several varieties of patterns were produced and attachment systems were introduced. Shingle sizes eventually became more varied. The greatest innovation in the asphalt shingle industry was the introduction of the multitab strip shingle. Bird and Son introduced the Neposet twin, which was a 12 ½ by 20 inch shingle with a slot tab that divided the piece to look like two shingles. Larger pieces made the price of installation decrease while the tab pieces imitated wood shingles. Prepared Roofing Manufacturers Association was later formed as a means to promote asphalt products as well as improve material quality. Also, asphalt shingles had a higher flame-resistance rating than wood shingles and were promoted by the manufacturers because of this fact. Pattern and size variety reached its highest point in the 1920s. Shingles could be diamonds, appear thatched, or even have scalloped edges. The use of different felt sizes and granule coatings helped to create a shadowed effect. The variations of tabs and interlocking shingles made it easy to install pieces in a straight line and protect against the pieces being lifted by strong winds. By the early 1930s, experimentation in sizes and shaped seemed to dwindle due to the upcoming Great Depression. Manufacturers had to cut their production and the building industry saw a dramatic decrease. Soon, a standard in shingle size was developed as being 12 by 36 inches, which was a multitab shingle and is still the industry standard today.

Though there was a dramatic decrease in size and shape variety, the amount of available colors seemed to grow exponentially. Colors were originally slate colored, which evolved to a variety of colors and blends. Decorative effects were available made from a wide variety of colors. Special rollers made it possible to put a texture on the top surface. The Ruberoid Company was the first manufacturer to offer asphalt shingles with a rolled wood-grain texture. At the end of the 1950s, 12-by-36 inch, multitab, blue shingles were the most popular roofing material.

In the 1970s, a glass fiber-reinforced felt was introduced. This material had increased tensile strength and was thinner and more light-weight. Several layers of these felts were laminated together to give a dramatic shading effect.

Manufacturing Process
Felt, which is the primary ingredient in asphalt roofing, was made originally of wool rags, cotton, or paper. Wood fibers later became the main ingredient. Felt is produced in a roll and then saturated with asphalt flux. Asphalt flux is a distilled crude oil. The saturated felt is then passed through a pan where the coating is applied. The coatings may have included mineral fillers like slate flour or powdered oyster shell. These materials helped to stabilize the mixture. The sheet was then passed under a shower of mineral or ceramic granules. Water was sprayed to cool the material, which was then rolled with a pattern to imprint either texture or patterns. The material was the cut with a rotary knife and possibly dusted with talc to keep the pieces from sticking to each other. Color could be created by adding fillers and granules in the desired colors. Colors varied depending on the fashion or regional preference as well as the available technology. Ceramic-fired granules were introduced around 1930 and produced colors of natural stones. Asbestos was added to some shingles to increase fire resistance.

Uses and Installation
Asphalt shingles were used in replacement of wood shingles due to affordability. The asphalt and fiberglass shingles dominated the residential roofing market since their introduction. Shingles should be installed in an overlapping method to help move water downward. Shingles have several small pieces and joints but depend on the overlapping installation to keep water from penetrating these spots. The amount of shingle exposed varied on every row. It was suggested that two layers of felt be used on low-sloped roofs. Shingles could also be fastened in a variety of ways. Originally, most shingles were nailed to the roof with the use of a tern-plate disk. The disks were made of a thick felt or cork. Large-headed galvanized roofing nails soon dominated the market as a method of fastening shingles. Spot cement could be applied after the shingles had been fastened, usually using a putty knife or caulking gun.

Conservation
Asphalt shingles durability relies heavily on how old the product is, how well it’s been taken care of, and how well it was made. Asphalts should be expected to change over time and are likely to experience weathering from physical and chemical means. Asphalt shingles are expected to last roughly twenty years before any serious signs of deterioration are obvious.

Deterioration
Moisture and drying phases can break down the asphalt-and-felt saturated base. While mineral and ceramic granules can resist exposure, asphalt and fiberglass are likely to degrade. Shingles are likely to warp or lose their granular covering if the soluble elements are allowed to be leached away. Also, shingles can curl if the felt is not properly saturated in the manufacturing process. Oxygen is likely to cause oxidation in the asphalt, which will lead to hardening in the shingles. Light is likely to promote this deterioration and the effects may be irreversible. Corrosive chemicals and organic growths may also affect the shingle’s durability.

Failure of asphalt shingles is not usually caused by the shingles but by the components of the system. Connections can become infiltrated with water. Flashing material is required when the materials connect to vertical surfaces adjacent to the roof. Flashing will work as a barrier against water infiltration. As the bituminous emulsion ages, it is likely to become brittle and less flexible. The material may crack the connection points. Separate flashing materials are the best type of roofing systems; it extends under and above the shingles and along an adjacent wall element.

Valleys are likely to experience twice the volume of rain water as regular shingles and are the most likely places to expect failure. Valleys with lapped shingles are more vulnerable to weather exposure. For these reasons, thicker shingles (known as valley linings) are suggested. Thermal expansion is likely to occur where a low slope roof meets with a steeper sloped roof. Also, these roof meetings are more likely to experience greater snow and ice buildup, which may result in leaking. Extra pressure added to a roof on extremely hot days can also cause damage; these are likely to include anything from a person walking on the roof or a large tree branch falling on the roof. Dented shingles are likely to lose granules, which will leave the felt exposed. Exposed felt is likely to increase the speed of deterioration. Walking on or hitting shingles on extremely cold days are likely to crack or break the shingles.

Conservation Techniques
The most common sign of shingle failure is a leaky roof. While finding the origin of the potential leak is suggested, individual shingles should also be investigated. A simple investigative technique is to scrape an individual shingle to understand how well the granules are adhering to the asphalt. Visual inspections are also helpful in identifying hardened spots and cracking. The extreme loss of granules or a buckling shingle may be signs of an impending failure. There are other ways for asphalt shingles to fail. Insufficient attic ventilation can shorten the life of shingles by causing condensation under the felt. This trapped moisture caused the roof and shingles to deteriorate.

Information on conserving individual shingles is limited since most information concentrates on preventing or stopping leaks. Paints and water repellents can help extend life of the shingles but is not a common practice. The addition of metal (zinc) strips along the upper portion of the roof has proved somewhat beneficial. During rain, the water washes minuscule quantities of metal down the shingles, which acts as a fungicide. During installation, the addition of a layer of rolled roofing below the areas of the roof that may be subject to ice dams can help prevent serious roof damage.

Regular maintenance, like cleaning gutters and downspouts can reduce damage. Trees and branches should be trimmed to prevent falling on the roof. Surface ventilation should be addressed to prevent prolonged moisture buildup. Downspouts from upper roof portions should never direct water on to lower roofs. If a shingle has been damaged, it should be removed. It is common practice to purchase extra packages of shingles in case damage occurs.

Algae discoloration is the most common conservation issue when dealing with an asphalt shingled roof. Algae discoloration presents as dark streaks and are products or growth and byproducts of airborne algae. Gloecapsa is the most common form of roof algae and is common in the southern and eastern coastal areas. Washing the roof with watered down household bleach should lighten the stain. Scrubbing and high-pressure washes are likely to be damaging as they will dislodge granules.

Replacement
If asphalt roofing has deteriorated beyond repair, it is time to install new roofing. New roofing can be placed over the existing roofing if the roof has only one layer of shingles, the decking is in good condition, and the roof structure is sound. Otherwise, remove the existing roofing and make any needed repairs before installing new roofing felt and shingles.

Replacement roofing that matches the historic appearance of American method shingle installation is relatively easy to find. Manufacturers are increasingly offering specialty shapes and interlocking shingles. For unique shapes or sizes, new shingles can be cut from roll roofing or tabless shingles using a utility knife.

Asbestos
Historically, asbestos has been used as an ingredient in several different asphalt roofing products. In 1990, U.S. EPA published a notice in the Federal Register identifying products made with asbestos. The asbestos National Emission Standards for Hazardous Air Pollutants (NESHAP) regulation lists the following asphalt roofing products as possibly containing asbestos:
 * Built-up roofing
 * Asphalt-containing single ply membrane systems
 * Asphalt shingles
 * Asphalt-containing underlayment felts
 * Asphalt-containing roof coatings and mastics
 * Asphalt-containing base flashings

While asbestos was commonly used in many asphalt roofing materials, asbestos was rarely used in the shingles themselves. It is acknowledged by the asphalt shingle manufacturers that between 1963 and the mid 1970s, some manufacturers did use asbestos in the fiber mat of shingles. The total asbestos content of asphalt shingles manufactured in 1963 was only 0.02 percent; in 1977, it dropped to 0.00016 percent. Unfortunately, less is known about the possible presence of asbestos in imported roofing coatings. Asbestos may also be present in the older bottom layers of roofing that has been built up over time.