Roofing in the United States

The United States has one of the largest roofing markets in the world and one of the widest ranges of roofing climates. It runs from the hurricane coasts of Florida and the Gulf through the hail belt of the Great Plains and the snowy north to the deserts and wildfire country of the West. American roofing history begins with the flat earth roofs of the Ancestral Puebloans. It continues through Spanish and English colonial traditions to the mass-produced asphalt shingle, which now covers most American houses, and the single-ply membrane, which dominates commercial flat roofs.³¹⁷⁸

Practice is shaped by model building codes that states and cities adopt, by insurers and their test-based ratings, and by a contracting industry organised around lightweight, quickly installed materials. Roofing is priced and ordered by the square, 100 ft² (9.29 m²) of roof surface. The unit appears even in historical production statistics.⁶²

Climate and hazards

Different hazards drive different roofs:

• Hurricanes. On the Atlantic and Gulf coasts, roof uplift and water entering through a damaged roof cause much of the storm damage. About 65% of the water striking an exposed roof deck gets into the house.¹¹ Florida's code history was rewritten by Hurricane Andrew in 1992.¹⁰
• Hail. Across the Plains and Texas, impact-rated coverings are in demand, and many insurers offer discounts for roofs rated UL 2218 Class 4.⁶
• Snow and ice. In the northern states and mountains, heavy snow loads, attic ventilation and eave protection against ice dams govern design. Some tile manufacturers do not allow direct-to-deck installation in climates prone to ice dams.¹⁴
• Wildfire. In the West, fire performance matters most. California's codes include wildland-urban interface provisions that roof products must meet.¹⁵
• Heat. In the South and Southwest, sun and heat shorten the life of shingles and membranes.⁶⁹

History

Ancestral Puebloan and Hispanic roofs

The oldest roofing tradition still in use in the United States is the flat earth roof of the Southwest. Ancestral Puebloan builders, between about 750 and 1300 CE, spanned rooms with peeled log beams (vigas) carrying smaller poles or boards (latillas). These were finished with brush and a sloped layer of earth for drainage and insulation, and viga ends or their sockets can still be seen in many ruins.⁴ Taos Pueblo in New Mexico, whose multi-storey adobe buildings date from the late thirteenth and early fourteenth centuries, has been continuously inhabited ever since. Its earthen buildings are kept in repair by periodic replastering. It is a UNESCO World Heritage Site and has been a National Historic Landmark since 1960.⁵

Spanish colonists adopted the method. From the seventeenth to the mid-nineteenth century adobe buildings in the Southwest were roofed almost entirely with flat earth roofs on vigas behind low parapets, drained by projecting canales.³ After the railroads arrived, hipped roofs, shingles, tile and sheet metal spread. Clay tile became widespread in southern California, and sheet metal became the most common covering in New Mexico.³ In the 1920s and 1930s the Pueblo Revival style brought back the flat roof and projecting vigas, though usually as ornament rather than structure.⁴ San Xavier del Bac, near Tucson, Arizona, built between 1783 and 1797 entirely of adobe, is among the region's great colonial buildings.³

Colonial wood, slate and metal

In the English colonies of the Northeast, early roofs were framed and boarded in the English manner, heavily enough to carry slate or tile. Timber was abundant, however, and hand-split wood shingles, smoothed with a drawknife, became the normal covering.¹ Oak and white cedar were used in southern New England and eastern white pine further north.¹ Sheathing changed from vertical boards in the seventeenth and eighteenth centuries to horizontal boards, often spaced apart, which ventilated the shingles and probably lengthened their life.¹ By about 1900, western red cedar shingles from the Pacific Northwest were readily available in the Northeast.¹

Slate appeared early. Roofing slate found at Jamestown, Virginia, dates from 1625 to 1670. There were slate roofs in Boston by 1654 and in Philadelphia by 1699, almost all of them using slate imported from North Wales.² Although slate was quarried in New England in the 1600s, transport problems kept it rare until after 1800. Then a series of devastating city fires encouraged, and in some places required, its use.¹ The first commercial American slate quarry opened in 1785 in Peach Bottom Township, Pennsylvania.² Quarrying spread through Vermont, Maine and New York in the first half of the nineteenth century.¹ By 1876 the country was a net exporter of slate. In 1899 more than 200 quarries were working in 13 states, with Pennsylvania the largest producer, and output peaked between 1897 and 1914.²

Metal arrived in stages. Sheet lead was imported from England in the seventeenth century but was costly. Sheet copper became available in the late eighteenth century, driven by shipbuilding, and was used mainly on complex roof forms.¹ By the mid-nineteenth century tin-plated and terne-coated (lead-tin) iron and steel sheet was in common use, mostly on low-slope roofs. Stamped metal "shingles" for steeper roofs followed late in the century.¹

The asphalt age

Asphalt-impregnated felts were introduced in the 1880s, at first as roll roofing.¹ Mineral granules were added to the surface in 1897, and strips were first cut in 1901.⁶ Henry Reynolds of Grand Rapids, Michigan, is credited with inventing the asphalt shingle, first used in 1903.⁶ By about 1915, three-tab strip shingles were on the market, coloured brown to imitate wood or red, black and green to imitate slate.¹ Production reached about 11 million squares by 1939.⁶ The slate industry declined from about 1915, as skilled labour became scarce and cheaper asphalt shingles took its market.²

The shingle's base mat changed too. Early shingles used cotton rag felt. Fibreglass mats appeared in 1960 and overtook organic felt by 1982, and the last organic-mat production ended in 2011.⁶

Modern commercial roofing

On low-slope commercial buildings, polymer membranes challenged multi-ply built-up roofing from the 1970s. EPDM single-ply roofs were introduced in 1962 and gained popularity after the oil embargo raised asphalt prices.¹⁷ TPO entered the American market in the early 1990s.⁹ By 2023 about 81% of commercial roofing contractors installed single-ply systems, which made up 36% of their commercial revenue. TPO led single-ply sales, ahead of EPDM and PVC.⁸

Roofing today

Houses

Asphalt shingles are used on more than 80% of American roofing and re-roofing projects on homes.⁷ They come in two main types. Thin, flat three-tab shingles typically last 15 to 18 years, and thicker, layered architectural or dimensional shingles 24 to 30 years.⁶ Most builders of new homes now use architectural shingles. Three-tab shingles remain common in re-roofing but have been losing popularity.⁷

Other coverings have smaller shares:

• Metal. Mostly painted steel in standing-seam or vertical-rib profiles, metal is gaining ground as both an accent material and a full re-roofing choice.⁷ Among contractors, 56% of residential roofers offered metal in 2023.⁸
• Concrete and clay tile. Tile is common in the Sunbelt, where concrete has displaced clay in most residential tile work.¹⁴ Its overall share has been declining.⁷ US codes treat properly installed concrete tile as a Class A fire-rated covering.¹⁵
• Wood shingles and shakes. Use has fallen sharply.⁷
• Slate. After its decline from about 1915, slate has regained some ground through the historic preservation movement.²

Commercial buildings

Large low-slope roofs are covered with single-ply membranes (TPO, EPDM, PVC), modified bitumen, built-up roofing or metal. About 79% of commercial contractors installed metal roofs in 2023, which accounted for 13% of their revenue.⁸

Condition of the housing stock

The American Housing Survey asks about roof problems rather than materials. Its 2023 data counted about 6 million households reporting roof leaks, 3.5 million with missing roofing material, 1.9 million with sagging roofs and 1.5 million with holes in the roof.¹³ Among the 15 largest metropolitan areas, Detroit, Philadelphia and Los Angeles had the worst combined roof-condition scores.¹³

Waste

Shingle roofs produce large amounts of waste. An estimate from 2007 put tear-off and manufacturing scrap at about 11 million short tons a year, mostly sent to landfill. Recycled shingle can be used in asphalt paving, but some states restrict this, partly because shingles made before the early 1980s may contain asbestos.⁶

Codes, standards and regulation

Model codes

Most American jurisdictions adopt the model codes of the International Code Council (ICC), often with local amendments.¹² The ICC was formed in 1994 by merging three regional code bodies: BOCA, ICBO and SBCCI. The first International Building Code appeared in 2000, and new editions have followed every three years.¹² Roof assemblies for houses are governed by the International Residential Code, and those for other buildings by the International Building Code. Product evaluation reports are written against the 2006 to 2024 editions of both.¹⁵

Product standards and ratings

• Asphalt shingles. ASTM D3462 covers glass-felt asphalt shingles. ASTM D3161 is a wind-resistance test, and ASTM D7158 sets wind classes D, G and H, for wind speeds up to 90, 120 and 150 mph.⁶
• Impact. UL 2218 rates impact resistance, with Class 4 the highest.⁶
• Concrete tile. Tiles are made to ASTM C1492.¹⁵
• Slate. ASTM C406 grades slate by service life, with S1 rated for more than 75 years.¹⁶
• Fire. Roof coverings are classified A, B or C. Codes recognise some materials as Class A without testing, others through ASTM E108 or UL 790 tests.¹⁶¹⁵
• Slate testing. Slate has been tested for hail and wind as well as fire. In FM 4473 testing, ⅜ in slate achieved Class 4 hail resistance. Slate nailed with copper nails passed ASTM D3161 Class F wind testing and resisted uplift to 160 mph.¹⁶

Florida

Before Hurricane Andrew struck in 1992, Florida had more than 400 separate county and municipal building codes and no uniform wind standard. The storm destroyed about 63,500 homes.¹⁰ In 1994 the South Florida Building Code created the High-Velocity Hurricane Zone (HVHZ), and Miami-Dade and Broward counties still apply its stricter rules.¹⁰ A unified statewide Florida Building Code, based on the International Building Code, took effect on 1 March 2002.¹⁰ Its 8th edition took effect on 31 December 2023, and the 9th is scheduled for 31 December 2026.¹⁰ Design wind speeds in Miami-Dade reach 165 to 185 mph (266 to 298 km/h), depending on the building's risk category.¹⁰ Roofing products must hold state or Miami-Dade product approval, backed by test protocols such as TAS 201, 202 and 203 for impact.¹⁰ A review after Hurricane Milton in 2024 reported that no homes built after the 2002 code were destroyed.¹⁰ About 4.7 million Florida homes predate it.¹⁰

Beyond code: FORTIFIED

The Insurance Institute for Business & Home Safety (IBHS) runs FORTIFIED, a voluntary programme that goes beyond code minimums. A FORTIFIED Roof has improved attachment of the roof sheathing, a sealed roof deck, better edge detailing and protection against attic vent failure.¹¹ IBHS reports that a sealed roof deck with improved attachment can cut water intrusion by up to 95%.¹¹ In Alabama, a 2019 law (Act 2019-240) requires homeowners' insurers to offer an endorsement that pays the extra cost of re-roofing to FORTIFIED standards when an insured roof is replaced. IBHS estimated that extra cost at $700 to $1,700 per roof, plus $300 to $600 for the required third-party evaluation.¹¹ FORTIFIED designations last five years.¹¹

Notable roofs

• Taos Pueblo, New Mexico. Multi-storey adobe buildings with earth roofs, continuously inhabited since the late 13th or early 14th century.⁵
• San Xavier del Bac, Arizona (1783–1797). A mission church built entirely of adobe.³
• Colonial slate roofs of Boston and Philadelphia. Documented by 1654 and 1699 respectively.²

Local roofing terms

• Square: 100 ft² (9.29 m²) of roof, the unit used in ordering, pricing and production statistics.⁶
• Viga / latilla (Spanish): the beam and the smaller poles of a Southwestern flat roof.⁴
• Canale (Spanish): a projecting roof drain on a flat adobe roof.³
• Three-tab and architectural: the two main grades of asphalt shingle.⁶
• HVHZ: Florida's High-Velocity Hurricane Zone.¹⁰