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Song bird perched on an ridge cap on a 3-tab asphalt shingle roof

沥青瓦是一种安装在墙壁或屋顶的瓦片状材料，由于其相对廉价和易于安装的特点，成为北美地区最为广泛应用的屋顶防水的材料。

历史

沥青瓦是一项美国发明，1901年首次应用，1911年在美国部分地区大规模应用。到1939年，总共有超过1.1千万块沥青瓦被生产出来。 沥青瓦的前身是一种1893年被称为“沥青预涂屋顶”，一种没有颗粒材料的“沥青卷屋顶”。 1897年，经过测试不同材质的颗粒的表现，包括云母，蚌壳粉，板岩，白云石，飘尘，石英石，粘土。颗粒状板岩被添加到了涂层表面用来增加这种材料的耐久性。1901年，这种材料的沥青涂层被裁剪成长条形,使用时可以单条或多条叠加使用。

所有的沥青瓦都是将有机物涂在基底材料上。最早的基底材料是毡制品，主要是以棉花为材料制成。但在十九世纪二十年代之后，棉变得越来越昂贵，替代材料开始出现。其他的有机物用作毡制品的有，羊毛，黄麻，马尼拉麻和纸浆。 1926年，沥青瓦研究机构和国家标准制订机构在测试22种基底材料后得出没有显著差异的结论。在五十年代，自封技术和手工涂抹的粘性剂的应用有效的阻止了大风对于沥青瓦屋顶的破坏。制订的自封条的标准是在140华氏度条件下6小时之内达到完全的黏合。同样是在五十年代，对于3/4英寸胶带的测试得出六张胶带的效果同四颗钉子效果相同。在1960年，无纺布基底材料的引入，曾带来一定的成功。生产出的更轻，更具弹性的沥青瓦被证明具有更强的抗风特性，特别是在零下的环境下。同样是在六十年代，又增加了对冰雹损害的评估，特别是冰雹大小超过1.5英寸。

All shingles were organic at first with the base material, called felt, being primarily cotton rag until the 1920's 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. In 1926 the Asphalt Shingle and Research Institute with the National Bureau of Standards tested twenty two types of experimental felts and found no significant differences in performance. In the 1950's 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 degrees Fahrenheit. Also in the 1950's testing on the use of 3/4 inch staples rather than roofing nails was carried out showing they could perform as well as nails but with six staples compared with four nails. In 1960 fiberglass mat bases were introduced with limited success, the lighter more flexible shingles proved to be more susceptible to wind damage particularly at freezing temperatures. Also in the 1960's research into hail damage which was found to occur when hail reach a size larger than 1.5 inches.

Asphalt Roofing Manufacturers Association (ARMA) formed the High Wind Task Force in 1990 to continue research to improve shingle wind resistance.

Types

A home in Avalon, NJ showing an asphalt shingle roof.

Two types of base materials are used to make asphalt shingles: A formerly-living organic base and fiberglass base. Both types are made in a similar manner with asphalt or modified-asphalt applied to one or both sides of the asphalt-saturated base, covered with slate, schist, quartz, vitrified brick, stone, or ceramic granules and the back side treated with sand, talc or mica to prevent the shingles from sticking to each other before use. The top surface granules block ultra-violet light which causes the shingles to deteriorate, provides some physical protection of the asphalt and gives the shingles their color. Some shingles have copper or other materials added to the surface to help prevent algae growth. Self-sealing strips are standard on shingles to help prevent the shingles from being blown off by 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 – Passed at basic wind speeds up to and including 90 mph; Class G – Passed at basic wind speeds up to and including 120 mph; and Class H – Passed at basic wind speeds up to and including 150 mph. 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 resistant to thermal cracking, as well as 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.

Organic

Organic shingles are made with a base mat of formerly living (organic) materials such as paper (waste paper), cellulose, wood fiber, or other materials saturated with asphalt to make it waterproof, then a top coating of adhesive asphalt is applied and ceramic granules are then embedded. Organic shingles contain around 40% more asphalt per square (100 sq ft.) than fiberglass shingles. The paper-based nature of "organic" shingles leaves them more prone to fire damage, and their highest FM rating for fire is class "B". Organic shingles are less brittle than fiberglass shingles in cold weather.

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. Also, some organic shingles produced before the early 1980s may contain asbestos.

Fiberglass

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.

Fiberglass shingles are slowly replacing organic felt shingles and by 1982 the production of fiberglass shingles overtook organic shingles. Widespread hurricane damage in Florida during the 1990's prompted the industry to adhere to a 1700-gram tear value on finished asphalt shingles.

Per 2003 International Building Code Sections 1507.2.1 and 1507.2.2, asphalt shingles shall only be used on roof slopes of two units vertical in 12 units horizontal (17% slope) or greater. Asphalt shingles shall be fastened to solidly sheathed decks.

Qualities

Asphalt shingles have varying qualities which help them survive wind, hail, or fire damage and discoloration.

• The American Society of Testing Materials (ASTM) has developed specifications for roof shingles: ASTM D 225-86 (Asphalt Shingles (Organic Felt) Surfaced with Mineral Granules) and ASTM D3462-87 (Asphalt Shingles Made from Glass Felt and Surfaced with Mineral Granules), ASTM D3161, Standard Test Method for Wind-Resistance of Asphalt Shingles (2005),
• Many shapes and textures of asphalt shingles are available: 3 tab, jet, "signature cut", t-lock, tie lock, etc. Architectural (laminated) shingles are a multi-layer, laminated shingle which gives more varied, contoured visual effect to a roof surface. These shingles are designed to avoid repetitive patterns in the shingle appearance. Special shingles are needed for the eaves starter course and ridge caps. Laminated shingles are heavier and more durable than traditional 3-tab shingle designs.
• Solar reflecting shingles help reduce air conditioning costs in hot climates by being a better reflective surface.
• Wind damage: Asphalt shingles come in varying resistance to wind damage. Shingles with the highest fastener pull through resistance, bond strength of the self seal adhesive, properly nailed will resist wind damage the best. Extra precautions can be taken in high wind areas to fasten a durable underlayment and/or seal the plywood seams in the event the shingles are blown off. UL 997 Wind Resistance of Prepared Roof Covering Materials class 1 is best Wind Resistance roof standard and ASTM D 3161 class F is best for bond strength.
• Hail damage: Hail storms can damage asphalt shingles. For impact resistance UL 2218 Class 4 is best. This increases survivability from hail storms but the shingles become more susceptible to hail damage with age.
• Fire resistance: Forest fires and other exterior fires risk roofs catching on fire. Fiberglass shingles have a better, class A, flame spread rating based on UL 790, and ASTM E 108 testing. Organic shingles have a class C rating.
• Algae resistance Algae is not believed to damage asphalt shingles but it may be objectionable aesthetically. Different treatment methods are used to prevent discoloration from algae growth on the roof. Moss feeds on algae and any other debris on the roof. Some manufactures offer a 5- to 10-year warranty against algae growth on their algae resistant shingles.
• Locking shingles: Special asphalt shingles are designed to lock together called tie lock or T lock.
• Durability Shingle durability is ranked by warranted life, ranging from 20 years to lifetime warranties are available. However a stated warranty is not a guarantee of durability. A shingle manufacturer's warrantie may pro-rate repair costs, cover materials only, have different warranty periods for different types of damage, and transfer to another owner.

Shingles tend to last longer where the weather stays consistent, either consistently warm, or consistently cool. Thermal shock can damage shingles, when the ambient temperature changes dramatically within a very short period of time. "Experiments...have noted that the greatest cause of asphalt shingle aging is thermal loading." Over time the asphalt becomes oxidized and becomes brittle. Roof orientation and ventilation can extend the service life of a roof by reducing temperatures. Shingles should not be applied when temperatures are below 10°C (50°F), as each shingle must seal to the layer below it to form a monolithic structure. The underlying exposed asphalt must be softened by sunlight and heat. A few shingle types utilize release tape which must be removed just prior to installation.

Left: Example of faster asphalt shingle wear along eaves due to channeled water running down the roof. Right: Severe shrinkage resulting in tearing away of entire flaps. Water running down the roof can seep around the exposed nails into the interior space.

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 rooflines 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.

Maintenance

Moss and debris which remains on the shingles will cause premature deterioration and should be physically removed from the roof or with a copper sulfate, zinc chloride or other solution carefully applied and thoroughly rinsed. To prevent the growth of algae and moss install zinc or copper strips or wire at the ridge and every four to six feet down the roof. Black algae growth can be cleaned with a bleach solution.

Disposal and recycling

A 2007 study done for the United States Environmental Protection Agency (EPA) titled "Environmental Issues Associated With Asphalt Shingle Recycling" provides the following information:

• Approximately 11 million tons of asphalt shingle waste is generated each year in the United States
• The most common disposal method for asphalt shingles in the US is landfilling. Waste asphalt shingles do, however, offer a strong potential for recovery and recycling with uses in hot mix asphalt (HMA), cold asphalt patching, and as a fuel in cement kilns.
• The main environmental concern in recycling asphalt shingles is the rare presence of asbestos in shingles manufactured before 1980. Asbestos was also used in some felt paper, roll roofing, roof paint, roof coating, caulking, and mastic.
• Asphalt naturally contains polycyclic aromatic hydrocarbons (PAHs) some of which are carcinogenic and may put recycling workers at risk. Leaching and airborn PAHs have remained below detectable levels in most testing.

External links

• Canadian Asphalt Manufacturers Association technical bulletins
• Asphalt Roofing Manufacturers Association Residential/Steep Slope Technical Bulletins
• National Roofing Contractors Association information on asphalt shingles
• The Center for Environmental Innovation in Roofing

Category:Roofs [en:Closed range theorem]