Two types of asphalt shingles are used: organic and fiberglass or glass fiber. Organic shingles are generally paper (waste paper) saturated with asphalt to make it waterproof, then a top coating of adhesive asphalt is applied and ceramic granules are then embedded. In the case of algae-resistant shingles, a portion of the granules contain leachable copper ceramically coated, designed to protect against discoloration from algae on the roof. This does not protect from moss growth but does slow the growth. Moss feeds on algae and any other debris on the roof. Most manufactures offer a 5- to 10-year warranty against algae growth.
Shingles are judged by warranty and ASTM test standards. Organic shingles contain around 40% more asphalt per square (100 sq ft.) than fiberglass shingles. But this extra needed asphalt makes them less environmentally friendly. The paper-based nature of “organic” shingles leaves them more prone to fire damage, and their highest FM rating for fire is class “B”. Shingle durability is ranked by warranted life, ranging from 20 years to 50 years; in some cases lifetime warranties are available.
Fiberglass shingles have a base layer of glass fiber reinforcing mat. The mat is made from wet, random-laid fiberglass bonded with urea-formaldehyde resin. The mat is then coated with asphalt which contains mineral fillers and makes the fiberglass shingle waterproof. Fiberglass shingles typically obtain a class “A” fire rating as the fiberglass mat resists fire better than organic/paper mats. Fiberglass reinforcement was devised as the replacement for asbestos paper reinforcement of roofing shingles and typically ranges from 1.8 to 2.3 pounds/square foot.
The older organic (wood and paper pulp product) versions were very durable and hard to tear, an important property when considering wind uplift of shingles in heavy storms. Fiberglass is slowly replacing felt reinforcement in Canada and has replaced mostly all in the United States. Widespread hurricane damage in Florida during the 1990s prompted the industry to adhere to a 1700-gram tear value on finished asphalt shingles.
A newer design of fiberglass asphalt shingle, called laminated or architectural, uses two distinct layers which are bonded together with asphalt sealant. Laminate shingles are heavier, more expensive, and more durable than traditional 3-tab shingle designs. Laminated shingles also give a more varied, contoured visual effect to a roof surface.
Traditionally, asphalt — also called composition — shingles were made by saturating a heavy layer of building felt (made from organic fibers) with asphalt. These asphalt-felt shingles have largely been
supplanted by fiberglass-based shingles. Instead of building felt, they have a fiberglass base impregnated with the asphalt. These shingles are more durable and will last twice as long as the felt-based shingles. In addition to the asphalt coating, the shingles also have a layer of ceramic and hard mineral granules. This layer adds color to the roofing material, but its main function is to protect the asphalt base from the intense ultraviolet radiation of the sun. The asphalt-saturated base is relatively impervious to rain and snow, but without the mineral coating it would quickly break down when exposed to the sun.
People assume that most roof damage comes from the wind, rain and snow. Indeed, these elements eventually erode the granular coating from the shingles, but it is the intense heat of the sun that does the
real damage. Thus the longevity of the roof covering is often determined by the amount of sunlight it is exposed to. On many houses the shingles on the northern side of the roof last longer than those on the
southern side, because they receive less sunlight. For the same reason, houses in the Southern states usually need roof replacement before those in the Northern states.
Other than planting shade trees near the house, there is little you can do to shield your roof from the sun. You can, however, make sure that the attic remains cool so that heat cannot rise through the sheathing to attack the shingles. The best way to do this is by installing vents in the attic. Adding soffit and ridge vents, for example, will allow cool air to enter under the eaves, flow along the underside of the roof and exit at the peak. This circulating air can lower roof temperatures by up to 20 degrees.
The protective nature of asphalt shingles primarily comes from the long-chain hydrocarbons impregnating the paper. Over time in the hot sun, the hydrocarbons soften and when rain falls the hydrocarbons are
gradually washed out of the shingles and down onto the ground. Along eaves and complex roof lines more water is channeled so in these areas the loss occurs more quickly. Eventually the loss of the heavy
oils causes the fibers to shrink, exposing the nail heads under the shingle flaps. The shrinkage also breaks up the surface coating of sand adhered to the surface of the paper, and eventually causes the
paper to begin to tear itself apart. Once the nail heads are exposed, water running down the roof can seep into the building around the nail shank, resulting in rotting of roof building materials and causing
moisture damage to ceilings and paint inside.
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