A roof system consists of various types of materials that are interconnected in order to provide weatherproof protection in buildings. In addition to being waterproof, roofs help protect buildings from the sun, rain, snow, and other elements.
Roofing materials vary depending on the shape of the roof, location and climate, and whether the use is for residential or commercial. Asphalt shingles are popular for residential use as they are fairly inexpensive and have a good lifespan. In commercial construction where flat roofs are more common, metal, EPDM, and built-up roofs are extensively used.
A wide variety of roof coverings exist today, each with its own advantages depending on the use. The most common roofing materials available include asphalt, wood, metal, clay, cement and slate, glass and plastic, and plastic liquid coatings.
Asphalt and coal-tar pitch are the bituminous materials used in built-up roofing. Both are solid at normal temperatures and are heated to a liquid state before application. Asphalt is typically preferred for sloping roofs and coal tar for flat roofs.
Built-up roofs consist of alternate layers of asphalt saturated felts and hot asphalt cement. They are designated as 3-ply, 5-ply, etc. depending on the number of layers used over the base layer nailed to the roof deck. The finish surface is composed of slag or stone chips set in a final flood coat to protect the plies from the weather.
Installation of asphalt shingles is done in a lapped fashion with galvanized roofing nails on roof decks having a pitch of at least 3:12. Asphalt strip shingles are typically manufactured with adhesive tabs along the underside. This allows them to adhere to the shingle strip below and prevents them from blowing off the roof during high winds.
Another type of asphalt roofing known as asphalt roll roofing is manufactured in rolls that are 36 inches wide, allowing it to be used on slightly to steeply pitched roofs. Similar to asphalt shingles in composition, they are also installed by lapping and nailing.
Wood shingles are made from decay-resistant wood species such as red cedar, cypress, redwood, etc. They are available in a variety of grades and are either machine-sawn or hand-split called shakes.
Wood shingles are applied both to roofs and walls over solid or spaced sheathing and fastened with aluminum or galvanized nails. The shingles are tapered in thickness, with the thickness of the butt (the thick end) expressed as the number of shingles required to produce a total thickness.
Wood shingles are typically installed on roofs with a slope of 4:12 or greater. In order to prevent cupping or rotating, they should be applied in a manner that allows for underside ventilation.
Fire can be a concern with wood shingles, however, they are often pressure treated with fire retardant chemicals to prevent combustion. An alternative method of application is to spray, brush or mop with fire retardant chemicals after installation. If cost is a consideration, wood shingle shake roofs can be relatively expensive.
Metal roofs are commonly used on flat roofs but can also be used on roofs with a pitch of 3:12 or greater. If used on flat roofs they are commonly either soldered or welded, while on pitched roofs they are attached with either nails or screws of the same metal.
Metal roofing materials include galvanized iron, copper, aluminum, and terne plate (steel coated with lead and tin). Also used, but less common, are lead, zinc, and stainless steel.
In order to allow for movement, various installation details exist. These include the standing seam, batten seam, and flat-locked seam roofing systems. Additionally, corrugated metal is designed to respond to thermal movement better than sheet metal due to the shape of the panels.
When used on flat roofs, metal tiles are either soldered or welded. On roofs with a pitch of 3:12 or greater, metal screws or nails are typically used.
Metal roofs tend to be relatively expensive, however, they are very durable and can last for many years.
Clay, Cement, and Slate
Clay roofing tiles are available in a wide range of earth colors, patterns, and can be glazed. They are manufactured from the same clays as bricks. Cement roofing tiles are manufactured from Portland cement and fine aggregate. They tend to be less expensive than clay tiles and also come in a variety of colors and shapes that resemble clay tiles.
Slate roofing tiles or shingles are quarried from natural rock and split into thin rectangular slabs. Sizes vary from about one-quarter inch to half an inch in thickness and an average dimension of about 12 inches by 16 inches. Slate is available in a variety of colors and textures from a rough surface to smooth.
Tile roofs, in general, tend to be heavy, very durable, fireproof, and relatively expensive. They are always applied to sloping roofs, lapped over the proceeding courses and attached with nails.
Glass and Plastic
Glass and translucent plastic sheets are used in skylights and clearstories or in industrial structures or greenhouses. Both plastic and glass have poor resistance to fire and therefore wire-reinforced glass and fiberglass-reinforced acrylic sheets are commonly used.
Skylights come in various shapes, including flat, domed, arched and pyramidal. They can also be either fixed or operational, providing venting through the roof in similar fashion to a window.
Available in single-ply sheets and in liquid form, plastic coatings can be rolled, sprayed, brushed, mopped, or troweled onto the roof, making them ideal on curved or difficult to get to surfaces.
Single ply sheets can also be insulated with foam. When the foam is thick, oftentimes heavy gravel or crushed rock is used to hold in place the plastic roofing.
Sustainable Roofing Materials
In addition to traditional roofing materials, new eco-friendly materials and roof systems are being explored. Roof gardens, for example, are becoming more common in buildings with flat roofs. They offer both an added functional amenity as well as improved heat control.
By absorbing more of the sunlight and reducing heat gain (heat island effect), roof gardens also help reduce the use of traditional cooling systems, such as air conditioning during the hot seasons. Roofing materials that are manufactured in light shades of color can have a similar impact by reducing the heat island effect.
In addition to thermal heat transfer control, new innovative roofing materials are being used to harness the energy of the sun to meet the energy demands of the building. Photovoltaic panels are being reimagined to take the form of more traditional roofing materials.
Roofs are the first layer of protection in a building. From sunlight, to rain, to snow, materials used in roofing are being constantly subjected to the elements. The selection of roofing materials, therefore, can have a big impact on the performance and lifespan of a building.
A wide range of roofing materials are available today. Their use varies depending on geographic location, roof shape, and desired look. In residential construction, asphalt shingles are most common due to cost and durability. In commercial construction where flat roofs are more common, metal, EPDM and built-up roofs are often used.
Newer roofing materials and methods of construction are also harnessing the energy of the sun and helping reduce the heat island effect on the surrounding environment. It is likely that in the future these new and sustainable roofing materials will continue to improve and help buildings achieve a carbon-neutral footprint. As such, roofing materials will be more efficient and likely be the primary source of energy production in a building.
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