Asphalt Shingle

An asphalt shingle is a thin, flexible roofing unit made of a reinforcing mat saturated or coated with asphalt (bitumen) and surfaced on its exposed face with crushed mineral granules. Shingles are nailed to a continuous wooden deck in overlapping courses, so that each course sheds water onto the one below and covers the nails of the course beneath.²⁴ In the United States they are often called composition or "comp" shingles, and the industry has long described them as the covering on roughly four out of five American homes; in 2009 the Asphalt Roofing Manufacturers Association put annual output at more than 12.5 billion ft² (about 1.16 billion m²), enough for over 5 million homes.⁵ In Europe the equivalent product is known as the bitumen shingle and is standardised under EN 544.⁶

The material is cheap to make and quick to install, comes in many colours and textures, and is light enough for ordinary timber roof framing. Its main limitations are a shorter service life than slate, tile or metal, sensitivity to heat and ultraviolet light, and a large end-of-life waste stream.²⁸

History

Asphalt shingles grew out of the American composition roofing of the mid-19th century. In the last quarter of that century manufacturers adapted the components of site-built "built-up" roofs into factory-made rolls sold as "ready roofing", today's roll roofing; asphalt, which could be processed to a firmer consistency than coal tar, made this possible.¹ An asphalt prepared roofing appeared in 1893, slate granules were added to its surface in 1897, and the material was first cut into strips in 1901.²

Herbert M. Reynolds of Grand Rapids, Michigan, is credited with making the first asphalt shingles in 1903 by hand-cutting stone-surfaced roll roofing into individual pieces.¹ Early shingles were rectangular or hexagonal and were made in red, green or black.¹ The multi-tab strip shingle, which gave the look of small shingles at a lower installation cost, followed soon afterwards, and in 1906 Bird and Son marketed a notched shingle that looked like two units once laid.¹

Several forces drove rapid adoption:

• Fire. In 1916 the National Board of Fire Underwriters called for wood shingles to be eliminated as a fire hazard, and asphalt products were promoted as the safer alternative.¹
• War. During the First World War asphalt shingles used materials not needed for the war effort and were easier to ship than wood or slate.¹
• Mail order. In 1926 Sears, Roebuck and Co. promoted slate-surfaced asphalt shingles in its catalogue of houses.¹
• Standardisation. By 1935 every major manufacturer offered the 12 by 36 in (305 by 914 mm) multi-tab strip, which remained the standard North American format for decades, and ceramic-coated granules broadened the colour range at about the same time.¹

Until about 1930 the Barber Asphalt Company advertised shingles made with natural asphalt from Trinidad's Pitch Lake, and the variety of shingle shapes and sizes on the market peaked around the same date; in the 1940s firms such as Flintkote still offered a wide range of shapes.¹ By 1939, production had reached about 11 million squares (roughly 100 million m²) a year.² Self-sealing adhesive strips arrived in the 1950s, glass-fibre mats were introduced in 1960, and by 1982 glass-fibre shingles had overtaken organic-felt shingles in use.² Organic-felt shingles are no longer made in North America, and their ASTM standard, D225, was withdrawn in 2012.³ Laminated "architectural" shingles have gradually displaced flat three-tab shingles on new houses. T-lock shingles, held by their hooked shape and fasteners rather than adhesive, ceased production around 2006, though many such roofs remain in service.¹⁰

Materials and construction

A modern shingle has four main parts:²⁷

• Reinforcing mat. Historically organic felt made from rag, paper or wood fibre; today almost always a glass-fibre mat. Canada's CSA A123.5 describes shingles of impregnated glass felt coated on both sides with asphalt.⁷³ European bitumen shingles may use mineral or synthetic reinforcement, or a combination.⁶
• Asphalt coating. Oxidised or polymer-modified bitumen, usually filled with finely ground mineral stabiliser, that provides the waterproofing.²
• Granules. Crushed and often ceramic-coated stone that shields the asphalt from ultraviolet light, adds colour and improves fire performance. Materials used over the years include slate, schist, quartz, vitrified brick, ceramics and others.² Some granules contain copper to inhibit algae.⁹
• Back surfacing and sealant. Sand, talc or mica keep bundled shingles from sticking together, and a factory-applied thermoplastic strip bonds each course to the one above once warmed by the sun.²³

Types

• Three-tab (strip) shingles: a single layer with two cut-outs forming three tabs, typically 12 by 36 in (305 by 914 mm) and weighing about 200 to 250 lb per square (roughly 9.8 to 12.2 kg/m²).¹⁰
• Laminated (architectural or dimensional) shingles: two or more bonded layers, the upper ones cut into shapes to create shadow lines; often metric-sized at about 39 by 13 in (about 1,000 by 333 mm) and weighing about 250 to 300 lb per square (about 12 to 15 kg/m²).¹⁰
• Premium or designer laminates: up to five layers, approaching 500 lb per square (about 24 kg/m²), and shaped to imitate slate or wood shake.¹⁰
• Individual and locking shingles: older or specialist forms, including hexagonal and T-lock patterns.¹¹⁰

A "square" is 100 ft² (9.29 m²) of roof, and is sold as three to six bundles depending on the product.¹⁰

Standards

United States. The International Residential Code requires asphalt shingles to comply with ASTM D3462, the standard for glass-felt shingles surfaced with mineral granules.⁴ ASTM D3462 sets minimum and maximum mass and physical properties and requires at least Class A fire resistance and Class A wind resistance (60 mph, 97 km/h).³ Two wind test methods are used:³⁴

• ASTM D7158 (an uplift method for self-sealing shingles): Classes D, G and H, corresponding to ultimate design wind speeds of 115, 150 and 190 mph (185, 241 and 306 km/h).
• ASTM D3161 (a fan-induced method): Classes A, D and F, corresponding to 60, 90 and 110 mph (97, 145 and 177 km/h).

The codes require the D7158 classification for shingles with factory self-sealing strips, with D3161 available for products outside its scope; for example, at an ultimate design wind speed of 168 mph (270 km/h) or above only Class H (or D3161 Class F) shingles may be used.⁴ Impact resistance is classified under UL 2218, with Classes 1 to 4 corresponding to impact energies of 3.53, 7.35, 13.56 and 23.71 ft-lbf; Class 4 is the highest.³ The UL 2218 classification system was established in 1996.²

Canada. CSA A123.5 covers glass-felt asphalt shingles, single- or multi-tab and single- or multi-layer, intended to be laid with at least a 50 mm (2 in) headlap.⁷

Europe. EN 544 specifies the properties, test methods, marking and conformity assessment of bitumen shingles for pitched roofs and wall cladding; it leaves design and installation to manufacturers and national rules, and requires each layer of a multilayer shingle to use the same reinforcement and coating.⁶

Installation

Asphalt shingles must be fastened to a solid deck of wood structural panels or lumber sheathing.⁴ Typical North American practice under the residential code is:⁴

1. Check slope. The minimum slope is 2:12 (about 17 percent, or 9.5 degrees). Between 2:12 and 4:12 two layers of underlayment are required, starting with a half-width strip at the eave and lapping each full sheet by half its width plus 2 in (51 mm).
2. Install ice barrier where required. In cold regions a self-adhering polymer-modified bitumen sheet, or two cemented layers of underlayment, runs from the eave to at least 24 in (610 mm) inside the exterior wall line, or 36 in (914 mm) along the slope on roofs of 8:12 or steeper.
3. Lay underlayment, drip edge and valley linings. Open metal valleys need a lining at least 24 in (610 mm) wide; closed valleys use roll roofing or self-adhering membrane at least 36 in (914 mm) wide.
4. Start at the eave with a starter course, then lay full courses upward, offsetting joints and aligning exposure to the manufacturer's marks.
5. Nail correctly. Nails must be galvanised steel, stainless steel, aluminium or copper roofing nails with at least a 12-gauge (0.105 in, 2.67 mm) shank and a 3/8 in (9.5 mm) head, long enough to penetrate 3/4 in (19 mm) into the deck or right through thinner sheathing. At least four nails are used per strip shingle, or more where the manufacturer specifies; above 21:12 the manufacturer's steep-slope instructions apply.
6. Flash walls, chimneys and penetrations with corrosion-resistant metal at least 0.019 in (0.48 mm) thick; sidewall base flashing must be at least 4 in (102 mm) high and 4 in wide.
7. Finish hips and ridges with cap shingles, often over a ridge vent.

Performance

Wind. Wind resistance depends on the sealant bond and fastening as well as the shingle itself. Basic three-tab shingles are designed for about 60 mph (97 km/h); laminated shingles are commonly rated between 70 and 130 mph (113 to 209 km/h) depending on the product.¹⁰

Hail. Hail damage to asphalt shingles has been found to begin with hailstones larger than about 1.5 in (38 mm), and impact-resistant shingles tested to UL 2218 Class 4 are offered in hail-prone regions.²³

Fire. Glass-mat shingles achieve a Class A fire rating, the highest under the US classification system, which ASTM D3462 requires as a minimum.³

Ageing. Heat and ultraviolet light drive volatile oils out of the asphalt; the shingle becomes brittle, granules wash into gutters, and the mat is eventually exposed. Manufacturer warranties on laminated products commonly run 30 to 50 years but are usually prorated.²¹⁰

Algae. Dark streaks on shingle roofs are usually caused by the airborne cyanobacterium Gloeocapsa magma, which thrives in warm, humid conditions and is common in the US Gulf states, along the north-west and eastern seaboards and in the Midwest. It is mainly cosmetic. Copper-bearing granules resist it; dilute bleach and trisodium phosphate solutions can lighten existing growth, while pressure washing is discouraged because it strips granules.⁹

End of life and recycling

Asphalt shingle waste is a large share of construction debris: a 2007 study estimated about 11 million short tons (10 million tonnes) of shingle waste a year in the United States, mostly landfilled.² Ground reclaimed asphalt shingles (RAS) can replace part of the binder and aggregate in road asphalt; 641,000 tons of unprocessed RAS were diverted from landfill in 2022, up 7 percent on 2021.⁸

Regional practice

• United States and Canada: the dominant residential roof covering, governed by ASTM D3462 and the IRC in the US and by CSA A123.5 and the National Building Code in Canada.⁵⁴⁷
• Europe: bitumen shingles are produced and sold under the harmonised standard EN 544, adopted nationally as, for example, SS-EN 544 in Sweden; they are used on pitched roofs and as wall cladding.⁶