Roofing Material Choices
There Are Many, Many Green Roofing Choices
Consider cost, production impacts, disposal, and maintenance
A variety of roofing products promise very long life, and, barring accidental damage, some should last virtually as long as the building. In addition to durability, other factors worth considering are the environmental impacts of production, service, and disposal; cost; whether the material can be recycled or reused; and how much maintenance it will require. In areas where cooling loads are very high, a reflective roof covering can reduce air conditioning costs substantially.
Vegetated roofs keep homes cool,cut stormwater runoff, and could last forever
Also called "living roofs," these consist of specially chosen plants in a growing medium suited to the climate and site. A living roof protects the waterproof membrane beneath it and could last indefinitely. Though they are more common in Europe, vegetated roofs are becoming a familiar sight in the U.S.
Residential living roofs usually are "extensive" systems — they have relatively thin soil coverings (up to 6 inches thick) and typically support low-growing plants such as succulents, moss, and grass. "Intensive" systems, found in commercial buildings, have enough soil to support trees.
Benefits of Living Roofs
Insulation value. A green roofRoof system in which living plants are maintained in a growing medium using a membrane and drainage system. Green roofs can reduce storm-water runoff, moderate temperatures in and around the building (by providing insulation and reducing heat island effect), as well as provide a habitat for wildlife and recreational space for humans. When properly constructed, green roofs can increase roof durability because the roof assembly’s air and water barriers are buffered from temperature fluctuations and UV exposure. lowers heating and cooling costs by providing an additional layer of insulation.
Long life. The soil and vegetation layer protects roof membranes from UV damage, potentially extending the life of the roof by 20 years or more, according to the U.S. Environmental Protection Agency.
Reduced stormwater runoff. Soil on a living roof retains rainfall and reduces runoff. A study of a 3,000-square-foot living roof in Philadelphia found that runoff was negligible when rainfall was 0.6 inches or less and overall was only about one-third of measured rainfall over an extended period. The roof was 2 inches thick and weighed less than 5 pounds per square foot when dry.
Even roof temperatures. At the same project, a neighboring black asphalt roof showed variations in temperature of up to 90° F, while the vegetated roof varied by only 18°.
Lower neighborhood temperatures. In urban areas, green roofs help to keep the air cooler by reducing the heat island effect produced by large tracts of concrete and asphalt.
On the downside, vegetated roofs are more complicated and expensive than conventional roof coverings and are likely to require specialists who can offer advice on roof loads, waterproofing, soil selection, and the types of vegetation that will prosper in a particular climate.
In many states, steel roofing is the greenest choice
Metal roofing is durable and lends itself to recycling, and a number of companies make roofing with as much as 100% guaranteed postconsumer recycled content. Metal roofing is resistant to fire, rot, and insects — and roofing that reflects a lot of sunlight can reduce cooling costs.
Metal roofs make excellent rainwater collection systems because of their smooth, clean surfaces. Snow slides off easily, a great advantage; but snow piling up around the base of a house can block doors and windows, and even cause structural damage if walls are not securely pinned to the foundation.
Materials-to-labor ratio: 65% materials/35% labor
Weight: 0.5 lb. to 1.75 lb. per sq. ft.
Most metal roofing is installed in long panels, which are either through-fastened or installed with standing seams and hidden fasteners. Metal shingles are also available.
Through-fastened panels are installed with roofing screws equipped with rubber washers. Standing-seam roofing is formed into long, shallow pans that are crimped together on the roof. Fasteners are concealed.
These roofs can be made from a variety of metals, including galvanized steel, stainless steel, and copper.
Given that metal is vapor impermeable, a designer must consider whether or not a roof assembly requires venting to promote drying. The decision depends on the type of metal roofing (metal shingles and corrugated through-fastened panels allow more airflow than standing seam) and the vapor profileA vapor profile is an assessment of the relative vapor permeabilities of each individual component in a building assembly and a determination of the assembly's overall drying potential and drying direction based on vapor permeabilities of all of the components. The vapor profile addresses not only how the building's enclosure assembly protects itself from getting wet, but also how it dries when it gets wet. For a detailed treatment of this subject, see Building Science Corporation's article Understanding Vapor Barriers. of the rest of the roof assembly. For example, back-venting roofing materials on structural insulated panel (SIP(SIP) Building panel usually made of oriented strand board (OSB) skins surrounding a core of expanded polystyrene (EPS) foam insulation. SIPs can be erected very quickly with a crane to create an energy-efficient, sturdy home. ) roofs is either strongly recommended or required by panel manufacturers.
Metal roof types
Most metal roofing is made from painted galvanized steel. Steel roofing that’s been galvanized or coated with an aluminum-zinc alloy called Galvalume is long-lasting.
The use of corrugated aluminum roofing, once a favorite for agricultural buildings, has been almost entirely eclipsed in recent years by other types of steel roofing. Because aluminum has a high coefficient of thermal expansion and contraction, fasteners undergo stress, subjecting the roofing material around fasteners to abrasion and wear, loose fasteners, or leaks.
Copper is the most durable roofing option and is easy to recycle. One potential downside is that water runoff contains ionic copper, which in high concentrations is harmful to sensitive aquatic life. Tests in the U.S. and Europe have helped produce models that predict how much copper is washed off a roof, although it’s not clear whether the amount of copper from an average-size house is an environmental threat. One study conducted at the University of Connecticut found that copper readily bonded to concrete and iron drainpipes and could be trapped by filters containing organic material.
Recycled rubber makes a great "slate"
Slate lookalikes made from recycled material are becoming increasingly common. Many have Class A fire ratings and Class 4 hail ratings (the highest), and come with 50-year warranties. They are an excellent alternative in areas where even fire-rated wood shingles are banned because of fire danger.
A number of companies produce roof shingles made from recycled plastic or a mix of plastic and wood fiber that approximate the traditional look of cedar or slate. Recycling plastic shingles when they eventually wear out is another environmental advantage.
As with plastic lumber, the long-term effects of UV light, and expansion and contraction of the material are still unknown.
Advantages of rubber or plastic shingles
Long warranties. Limited warranties of 50 years are common, representing a longer life span than most types of wood roofing, with lower maintenance. (Roofing warranties are more of a marketing ploy than a scientific estimate of service life, however, so warranty promises should be taken with a grain of salt.)
Good use of plastic. Like wood/plastic composite decking, roof shingles made from recycled material reduce the volume of waste that ends up in landfills and incinerators. Recycled content can be high, as in Ny-Slate shingles that are made from 100% postconsumer recycled carpet.
Lighter than slate. Plastic offers a way of getting the look of slate without the heavy weight. EuroSlate roofing, for example, made with tire crumb rubber and other recycled material, weighs less than 4 pounds per square foot.
Prices should be roughly in line with wood, metal, and high-end concrete tile roofing.
Locally harvested wood roofs can be a green choice
Cedar shakes and shingles make a long-wearing roof that’s lightweight and easy to repair. White oak roofs have lasted hundreds of years in Europe. Shingles can be made from many species of wood, and there are suppliers in local markets who take advantage of what grows in their areas.
In the U.S., wood shingle roofs are usually made from red or white cedar. Red cedar shingles make a handsome roofing material that lasts a long time when properly installed. The problem is that the best grades of red cedar — all-heart, vertical grain — typically come from old-growth forests, which by definition are not a sustainable supply source. Red cedar shingles certified by the Forest Stewardship Council(FSC) Nonprofit organization that promotes forestry practices that are sustainable from environmental and social standpoints; FSC certification on a wood product is an indicator that the wood came from a well-managed forest. (FSCNonprofit organization that promotes forestry practices that are sustainable from environmental and social standpoints; FSC certification on a wood product is an indicator that the wood came from a well-managed forest.) appear to be rarely if at all available.
Materials-to-labor ratio: 60% materials/40% labor
Weight: 0.35 lb. to 1.5 lb. per sq. ft.
Steep roofs are better for wood shakes and shingles. Most experts recommend a minimum slope of 6:12 for a trouble-free installation. Wood shingles should never be installed on a roof with a pitch that is shallower than 3:12.
Let the shakes and shingles dry evenly, or they'll twist, cup, and crack. To let them dry, wood shingles were traditionally installed over gapped sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. . Cedar Breather, a nylon matrix that provides an air space between the shingles and sheathing, can help make the roof last longer. Copper or zinc flashing and ridge caps can retard the growth of moss.
Debris leads to decay. Leaves and other organic debris collect moisture that can rot the roof prematurely. Valleys should be swept or cleaned every so often. Depending on where they are installed, wood shingles may also need periodic cleaning to remove moss, and shingles that crack or curl should be replaced.
Types of wood roofing
In addition to red cedar shingles, these other possibilities are also available:
Eastern white cedar has been a common siding and roofing material in the Northeast for over 200 years. Eastern white cedar is not as threatened as western red cedar, and the species can be sustainably harvested. There are several companies that produce FSCForest Stewardship Council. An independent, nonprofit organization that promotes responsible forest management through the use of a third-party certification process. FSC certification includes a chain-of-custody requirement that tracks sustainability of wood products from growth to end use.-certified shingles, including Maibec, and Koenig Cedar Co. Prestained shingles are available.
Alaskan yellow cedar. This is a Western wood that grows in a limited coastal range. It often has very tight growth rings and is exceptionally resistant to decay. This species faces the same environmental hurdles as western red cedar, although large tracts of standing deadwood in southeastern Alaska would offer some intriguing possibilities if consumers proved willing to pay the extra costs associated with helicopter-yarding.
Treated pine. Shingles cut from plantation-grown southern yellow pine and pressure treated with preservatives have warranties of up to 50 years. Treated pine costs somewhat less than cedar. Like pressure-treated framing and decking, this material doesn’t have high decay resistance unless it is treated, and it will have a lower percentage of vertical grain material than cedar.
Roof tiles weigh a lot but are fire resistant
Developed 5,000 years ago, roof tiles are heavy, but they have high fire and wind resistance and last a long time. They are produced in a range of shapes, colors, and finishes.
Clay roofing tiles have a long history in some parts of the U.S. They are simple to manufacture from locally available materials and are useful for limiting solar heat gainIncrease in the amount of heat in a space, including heat transferred from outside (in the form of solar radiation) and heat generated within by people, lights, mechanical systems, and other sources. See heat loss.. The range of available colors and finishes is extensive. When installed properly, the tiles are extremely durable, although somewhat fragile.
Clay roofing tiles have been almost entirely eclipsed by concrete roofing tiles, which are available for about half the cost. Concrete tiles have many of the same qualities as clay tiles, including high resistance to fire and wind.
Tile roofs can withstand 125 mph winds, according to tests by the Tile Roofing Institute. The roofs were installed with wind clips and strategically placed adhesive. Some tile can weigh up to 18 pounds per square foot. Manufacturers also offer lightweight versions that weigh between 5 and 7 pounds per square foot, about double the weight of a heavy asphalt roof.
two types of roof tile
Concrete tiles can be made to look like slate or cedar, broadening their appeal beyond the traditional Mission-style homes of the West. Manufacturers say that concrete tiles are resistant to hail as well as freeze-thaw cycles.
Clay tiles have at least one major advantage over concrete tiles: They hold their color over time. According to many roofing experts, clay tiles are probably more durable than concrete tiles, which have an expected life span of between 30 and 50 years.
Concrete tiles are available in three profiles: Mission S-tiles, villa tiles (low tiles with a shallow double-S profile), and flat tiles.
Clay or concrete tiles should be installed on roofs with a slope greater than 3:12.
Clay and concrete roofing tiles can break when stepped on. Once in place, however, they make for a robust, durable roof.
Concrete tiles can be installed with or without 1x2 battens. When used, battens are installed parallel to the eaves. Free-draining roof battens can make a roof more durable and improve water-runoff management.
For underlayment, most tile manufacturers recommend, at a minimum, one layer of #30 asphalt felt. Many roofers prefer to use #40 felt, a specialty underlayment available in areas where concrete tiles are common.
Plumbing vent pipes generally require two layers of flashing. The primary flashing is usually a galvanized steel boot that is integrated with the asphalt felt layer. The secondary pipe flashing is installed at the same time as the tiles.
Because the state of California has a long history of incentives for the installation of photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. (PV) systems, many PV manufacturers have concentrated their marketing efforts in that area, where concrete tile roofs are common. That's why most available roof-integrated PV modules (which do double-duty, producing electricity while acting as roofing) are designed for use on concrete-tile roofs.
Among the manufacturers offering PV modules designed for integration with concrete-tile roofing are BP Solar, GE Energy, Kyocera, MSK Corporation, Powerlight, and Sharp Solar.
Slate is beautiful, durable, and expensive
To many eyes, slate is the most beautiful roofing option. The relatively soft rock is sliced into thin sheets to form an extremely durable roof covering in a variety of natural colors. With care, it can be used over and over again. But for most builders, slate is a prohibitively expensive option.
Slate doesn’t undergo much processing before it’s used as roofing. And a service life of 100 years is not a stretch. Slate is a relatively loose-fitting roofing material that is vapor permeable with a great drying potential, so much so that the substrate can last as long as the claddingMaterials used on the roof and walls to enclose a house, providing protection against weather. .
Slate is nontoxic, and it can’t burn, rot, or be consumed by insects. Depending on where it’s quarried, slate comes in a wide range of colors, including black, gray, green, and red, and it can be cut in decorative patterns. Because it lasts so long, slate is often removed from one building and used on another, and there are a number of companies that specialize in salvaged slate tiles.
Traditionally, slate shingles (like cedar shingles) were installed on skip sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. , shingle-style, beginning at the eaves. Between one-third and one-half of the slate is exposed to the weather.
Materials-to-labor ratio: 60% materials/40% labor
Weight: 6 lb. to 11 lb. per sq. ft.
Must be installed with high-quality fasteners and flashing materials. In most cases, slates are installed with copper nails. Valleys, ridge flashing, and step flashing should be made of copper, weighing at least 16 ounces per square foot.
Finding a skilled installer can be difficult, especially in regions where slate doesn’t have a local history.
Slates are brittle and can crack if they’re walked on, making installation and repairs a challenge.
Asphalt shingles are affordable and easy to install
Asphalt shingles account for about 60% of the residential roofing market. They do have positive attributes: Thin, three-tab shingles are among the cheapest roofing options available; they are easy to install and repair; and they don’t require any maintenance. Installers are plentiful.
It's estimated that old roofing shingles account for up to 11 million tons of waste each year, much of which is not recycled. For those reasons, BuildingGreen's Residential Green Building Products recommends avoiding asphalt shingles altogether.
Asphalt shingles are often replaced for aesthetic reasons before reaching the end of their useful lifespan. The most common aesthetic problem is staining caused by algae. The use of metal ridge flashing will reduce algae growth on asphalt shingle roofs.
To reduce costs, manufacturers have lowered the asphalt content and increased the percentage of filler in many types of shingles. This trend may account for the increase in complaints about algae staining.
There is no consensus on whether organic-mat shingles have longer or shorter life spans than fiberglass-mat shingles.
Do warranties matter? Roofing consultants agree that asphalt shingle warranties are marketing tools, not scientific estimates of the product's likely life span. Most asphalt roofing warranties are prorated over time and do not cover labor, so they are unlikely to be of any value when needed.
Materials-to-labor ratio: 40% materials/60% labor
Weight: 3 lb. to 5 lb. per sq. ft.
Light shingles are cooler, but not much. If you live in a hot climate and are considering asphalt shingles, their color may help cut cooling costs. White asphalt shingles don't have a much higher solar reflectance than darker asphalt shingles. The solar reflectance of white shingles is not much more than 30%, while other colors vary from 5% (black) to 15% (red). One company, ISP Minerals, has developed a whiter roof granule that could be used to make white asphalt shingles that have a solar reflectance as high as 50%.
Heavy shingles may last longer. Unfortunately, little research has been conducted on the question of whether shingle longevity correlates to shingle weight. Owens Corning and CertainTeed are among companies making asphalt shingles that weigh up to five pounds per square foot, more than double the weight of a shingle with a 20-year warranty. More asphalt and multiple fiberglass mat layers make these heavier shingles stronger and more wind-resistant.
Shingle recycling is becoming more common. The prospects for asphalt-shingle recycling are improving. Shingles are between 19% and 36% asphalt by weight, so the roughly 12.5 billion square feet of shingles produced every year in the U.S. represent a sizable amount of petroleum. As the price of oil rises and its availability declines, recycling should become more financially attractive.
Concerns over asbestosMineral fiber once commonly used in many building materials, including insulation, fireproof siding, and resilient flooring. Inhalation of invisible asbestos fibers can lead to chest and abdominal cancers as well as scarring of the lungs. The use of asbestos in some products has been banned by the EPA and the U.S. Consumer Products Safety Commission; manufacturers also have adopted voluntary limitations on its use. When found in older buildings (most commonly in floor tiles, pipe and furnace insulation, or asbestos shingles), the product's friability is a major determinant in how it must be handled during renovations. More information: http://www.epa.gov/iaq/asbestos.html content in old roofing shingles have proven largely unwarranted. More states are working on road specifications (“roofs to roads”) that accommodate a blend of recycled asphalt shingles. (For more information on the future of asphalt shingle recycling, visit http://shinglerecycling.org). When ground into small pieces, waste shingles can be used for new hot-mix asphalt, cold patch, as temporary road surfaces, and even as fuel in cement kilns. Recycling old shingles into new ones, though, has proved problematic.
A more friendly shingle? One company —Tallant Industries of Fredericksburg, Va.— makes roofing shingles that are 50% asphalt and 50% cellulose fiber. All of the cellulose is postconsumer recycled waste.
ABOUT ROOFING CHOICES
ROOFING CHOICES AND BUILDING CODES
Clay and concrete tile roofs may be installed on solid sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. or spaced sheathing boards on roofs pitched 2.5/12 or greater. Roofs with a pitch of less than 4/12 require double-coverage underlayment (905.3.3.1); roofs pitched at 4/12 and greater require one layer (905.3.3.2). Tile-attachment methods vary with climatic conditions, roof slope, underlayment system, and tile type. Consult IRCInternational Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code. Section 905.3.7 and Table 905.3.7 for guidance on proper attachment methods. Flashing and counterflashing should be provided at walls and vertical penetrations. Valley flashing must be at least 26-gauge “W” profile, G90 galvanized sheet and extend 11 inches in both directions from the valley's centerline (905.3.8).
Slate is covered in Section 905.6 of the 2006 IRC. Slate must be installed with two nails on solid sheathed roofs of at least 4/12 pitch (905.6.2), with an ASTMAmerican Society for Testing and Materials. Not-for-profit international standards organization that provides a forum for the development and publication of voluntary technical standards for materials, products, systems, and services. Originally the American Society for Testing and Materials. D 226, Type 1 underlayment (905.6.3) underneath. Roof areas with a history of ice damming must have two layers of underlayment cemented together or a self-adhering, bituminous membrane extending from the roof edge to 24 inches beyond the building’s exterior wall line. Head lap requirements vary with roof pitch and can be found in Table 905.6.5. The minimum standard for valley flashing is 15-inch, G90 galvanized steel of .0179-inch thickness (905.6.6).
Asphalt roof shingles
Asphalt shingles (Section 905) must be installed on solid sheathed roofs of at least 2/12 pitch with 12-gauge roofing nails long enough to go through the shingle and penetrate the roof deck 3/4 of an inch. Roofs under 4/12 pitch require two layers of underlayment; roofs 4/12 and steeper require one layer. Roof areas with a history of ice damming must have two layers of underlayment cemented together or a self-adhering, bituminous membrane extending from the roof edge to 24 inches beyond the building’s exterior wall line.
Open and closed valleys are covered in Section 905.2.8.2, with approved valley flashing materials identified in Table R905.2.8.2.
ENERGY STAR: Information on all roofing products that meet the Energy Star criteria for “cool" roofs.
GreenRoofs.com: Companies that supply the components for vegetated roofs, including geotextile fabric, plastic and metal trays that hold soil and plants, and the plants themselves.
ShingleRecycling.org: State-by-state list of asphalt-shingle recycling programs and contacts, along with helpful background papers.
Lawrence Berkeley Lab: The solar properties of asphalt shingles.
University of California Fire Center: Great information on fire-safe details for concrete and clay tile roofs.
BattensPlus.com: One type of free-draining furring strip that is well suited to concrete and clay tiles.
The Cedar Bureau's list of Forest Certified Products
American Slate Co., Baltimore
Evergreen Slate Co., Granville, N.Y..
Greenstone Slate Co., Poultney, Vt..
Joseph Jenkins Slate, Grove City, Pa..
New England Slate Co., Poultney, Vt..
North Country Slate, Toronto, Ont., Canada.
- Krysta S. Doerfler/Fine Homebuilding #185
- Daniel S. Morrison/Fine Homebuilding #177
- Roe A. Osborn/Fine Homebuilding #134
- Charles Miller/Fine Homebuilding #179
- Dan Morrison/Fine Homebuilding #185
- Courtesy of Tile Roofing Institute/Fine Homebuilding #185
- John Mahan/Fine Homebuilding #185
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