Of all the common materials used in construction, none poses quite the challenges of roofing—particularly from an environmental standpoint.
Roofs provide one of the most fundamental functions of a building: shelter from the elements. Roofs must endure drastic temperature swings, long-term exposure to ultraviolet (UV) light, high winds, and extreme precipitation. Yet much of the roofing industry is driven by highly competitive economics and thin profit margins that conflict with these performance and durability requirements. As a result, roofs commonly exhibit the lowest durability of any major building component except carpeting, requiring and frequent replacement. The National Roofing Contractors Association (NRCA) estimates that 78% of the dollars spent on roofing in the U.S. are for reroofing, as opposed to roofs on new buildings.
Given the enormous ongoing investment of resources, energy, and dollars in resurfacing worn-out roofs, any measures that will increase a roof’s longevity are environmentally desirable. Aside from simply investing in better (and usually more expensive) materials, there are some specific regional and climatic considerations that can affect product durability. For example, some products may stand up well to intense heat and ultraviolet radiation from sunlight, but succumb quickly to repeated freeze-thaw cycles. A product’s resistance to natural hazards such as hurricanes, hail, and fire must be taken into account where appropriate. Finally, a roofing surface is only the most visible part of a complete roofing system, and the system is only as good as its weakest link. Thus, flashing details should be designed with the longevity of the roofing material in mind, accommodating any foreseeable maintenance requirements.
In comparing roofing materials, one should consider the natural resources, energy, and manufacturing requirements of various materials, as well as the quantity and toxicity of any pollution generated. Products made from limited or ecologically sensitive resources should be avoided where possible. Products manufactured locally of regionally available resources will consume less energy for transportation, a factor that is especially important with the heavier materials.
To the extent that a product contains recycled materials, it will usually have fewer manufacturing impacts, as well as reduced impact on our landfills. How easily a product can be recycled itself at the end of its useful life is also important, lest it create its own solid waste problem. At present about 32% of residential reroofing jobs simply cover the existing surface, rather than tearing it off. This practice saves money and landfill space in the short term but may be exacerbating future disposal problems unless roofing material recycling increases dramatically.
Recently it has been established that some roofing materials can help to reduce cooling loads (or simply increase comfort in hot weather) by reflecting solar radiation rather than absorbing it. Research done at the Florida Solar Energy Center indicates that the temperature in attics under roofs that effectively reflect sunlight may be up to 30°F (17°C) cooler than conventional roofs. How significant this is depends on the effectiveness of the insulation between the attic and the living space. In new, well-insulated buildings the difference in heat gain may not be very significant, but reroofing some older buildings with a reflective material can be as effective as adding attic insulation—and less expensive.
Finally, roofs are increasingly being recognized as potentially much more than protective shelters. Some of the elements they protect us from, especially sun and rain, can be collected and utilized to reduce a building’s dependence on polluting fuels or limited fresh water. Solar domestic hot water systems are desirable in many parts of the country, and rooftop photovoltaics—while expensive—are growing ever more feasible. Rather than simply mounting such systems on top of a roof, where their penetrations often impinge on durability, there is increasing interest in integrating such functions into the roof surface.
Collecting rainwater off roofs for irrigation and other secondary water uses is also increasingly popular. In some areas, rainwater catchment is a time-honored source of potable water. In densely developed areas, rainwater catchment has the added benefit of reducing stormwater runoff.
The roofing industry distinguishes between low-slope materials—those used on slopes of less than 3:12, or 25% (commonly misnamed “flat” roofs), and steep-slope materials—those used on steeper planes. The scope of this article is limited to steep-slope materials. The standard American unit of roofing materials, the square, refers to the amount of material required to cover 100 ft2 (9.29 m2) of roof surface.
In the U.S. a total of $16.1 billion dollars was spent on roofing contracts in 1994, $5.1 billion of which was for projects utilizing steep-slope materials, according to data from the NRCA. Figure 2 shows the relative market share of various roofing materials in dollars spent on the installation of each type. Although data on quantities of each type of roofing are unavailable, it can be assumed that because asphalt shingles cost less per square than most alternatives, they represent an even bigger fraction of the total materials used than the 75% indicated here.
Asphalt shingles consist of a fibrous mat with an asphalt coating.
The coating is then covered with mineral granules which protect the asphalt from UV degradation. Traditionally an organic felt material was used, made from wood, paper, or other organic fibers. In the 1980s fiberglass mats became more common and have largely replaced the organic felts.
Organic felts often include recycled paper fibers. The CertainTeed plant in Shockapie, Minnesota, for example, uses old corrugated cardboard and mixed paper waste for a majority of its fiber, according to Plant Manager Clem Carfrey. Most of the remaining fiber is from wood chips from debarking operations. Glass fibers for the fiberglass mats are made primarily from silica sand, limestone, and boron. Unlike with fiberglass insulation, little if any recycled glass cullet is used to make these fibers. Glenn Lamb, a senior engineer at Owens Corning Residential Roofing Products Division, speculates that recycled glass isn’t used because the fibers used for shingles are more sensitive to impurities. Another explanation for the lack of recycled content is that consumer demand and government procurement guidelines haven’t pushed the industry in that direction as they have with insulation.
Both types of mats are produced in a process similar to paper-making—the fibers are mixed with water to create a slurry, which is then laid out on a belt, drained, and dried. To bond fiberglass into a mat there is the added step of flooding the mat with a binder solution. The excess binder is then removed and the mat goes through an oven in which the binder is cured.
Asphalt for the shingles comes from petroleum refineries, where it is made from the residues remaining after the various grades of fuel and lubricating oil have been distilled out. Organic felts are saturated with a relatively light, saturation asphalt to give them moisture resistance. Both types of mats are then coated with a weathering asphalt, which has been hardened through oxidation to reduce its tendency to flow. The weathering asphalt is also mixed with a mineral filler or stabilizer, usually dolomite, limestone, or rock dust. This filler improves its weathering characteristics and provides fire protection. The glass mats are actually filled with weathering asphalt, while the organic felts, which are saturated with the lighter asphalt, are coated with a thin layer of weathering asphalt on the bottom and a thicker layer on top.
The asphalt-coated mats then receive a layer of granules, which can be any mineral that crushes into a cube shape. These granules are coated with a ceramic-type paint and fired in a kiln to achieve specified colors. Shingle manufacturers generally all purchase the granules from one of the few suppliers, such as 3M Corp. Less expensive, uncoated granules are used for sections of the shingles that won’t be exposed. Some companies, including CertainTeed, use granules made from coal-fired-boiler slag, an industrial waste, for this purpose. The completed shingles also receive a small bead of glue-down asphalt to seal the tabs, a strip of plastic release tape, and a backdusting of sand or talc to prevent them from sticking together in the package.
Table 1 shows the typical breakdown of the major components of asphalt shingles.
From an overall resource perspective, asphalt shingles are fairly energy-intensive to produce. Embodied energy data published by Richard Stein and Diane Serber in 1976 estimates the embodied energy of organic shingles at 25,000 Btu/ft2 (284,000 kJ/m2). As large as the roofing industry is, it uses only a fraction (about 4 million tons—3.6 million tonnes) of the 34 million tons (31 million tonnes) of asphalt used in the U.S. annually, and not all of that amount goes into shingle manufacture. Of the raw materials used to make shingles, only the petroleum used to make asphalt is known to be a limited resource.
On the disposal end, the main problem with asphalt shingles is that large quantities are replaced each year, taking up substantial landfill space. One layer of asphalt shingles on a roof can usually be simply covered by another; once two layers are down, removal is usually required before reroofing. Recycling of used shingles is currently possible only in New Jersey, though the company doing it, ReClaim, Inc., is now building a facility in Tampa, Florida. ReClaim uses the shingles to make pavement patching materials and a low-end paving material that competes with unpaved gravel for low-traffic areas (see EBN Vol. 1, No. 3).
Both organic and fiberglass asphalt shingles are available in flat strips, often with three tabs separated by notches, and in laminated versions that provide more texture, sometimes simulating wood or slate shingles (see figure 3). The flat shingles are typically available with 20-, 25-, or 30-year warranties, while warranties for the laminated versions range from 25 to 40 years.
The enormous cost pressure on materials at the low end of the price range makes quality difficult to maintain. Glenn Lamb points out that the cost of three-tab asphalt shingles today is roughly the same as it was 20 years ago. “If industry would just let the price move with inflation, you could have a vastly superior product,” he notes. Manufacturers are so driven to reduce costs, especially on their least expensive product lines, that occasional quality problems are all but inevitable. To builders and roofers who buy the least expensive, 20-year, shingle and then complain about quality or installation difficulties, Lamb suggests: “Why don’t you buy a 25-year product, and your problems are all solved?” Which isn’t to say, Lamb insists, that the 20-year shingle won’t do the job; it’s just that there is much less margin for error. With the newer laminated or “architectural” asphalt shingles, designed to create more texture on the roof surface, Lamb suggests that the 25-year economy version suffers from the same price pressures as the 20-year three-tab shingle. Lamb’s opinions are substantiated by recently published independent test results concerning tear strength. According to a report from the Midwest Roofing Contractors Association, none of the 20-year three-tab fiberglass shingles or 25-year laminated fiberglass shingles tested met the ASTM standard for tear strength, though several of the 25-year three-tab fiberglass shingles did.
When the environmental cost of relatively frequent replacement is factored in, no 20-year or 25-year asphalt shingle can be considered a good environmental choice. The more durable products may be an acceptable option, however. Comparing organic to fiberglass mats also reveals no easy answers. Organic felts use recycled materials, and they don’t exhibit the tear-strength problems described above for fiberglass (all organic shingles tested easily surpassed the ASTM standard). As a result they may be more appropriate for use in high-wind areas. Manufacturing organic shingles does require significantly more asphalt overall, even though they contain less weathering asphalt, which may reduce their durability.
Clay roofing tiles are common in warmer climates, although technically those with a low water absorption rating can be used anywhere.
Tiles with higher water absorption are more susceptible to freeze-thaw damage. Building codes typically allow tiles with water absorption below 6% to be used in any climate, but the durability of these may still be compromised. One of the most expensive products, from Ludowici (now owned by CertainTeed, Inc.) has very low water absorption (about 0.1%). These tiles are quite resistant to freeze-thaw damage, but even they, after 100 to 125 years, inevitably succumb to damage from repeated freezing and thawing, according to Jim Crawford of the company.
Tiles are made by simply shaping and firing clay. The quality of tile products depends mostly on the quality of the clay and the temperature at which it is fired. Some tile products have a small amount of barium carbonate added to prevent efflorescence (white crystals formed by salts emerging from the clay). Ludowici tile is fired using natural gas in a 24-hour cycle, during which it stays at 2100°F (1150°C) for over four hours. These tiles are sold with an unusually long 75-year warranty, and cost from $300 to $1200 dollars per square to purchase (see figure 1, page 1).
Clay tile comes in many shapes, not only the traditional Mediterranean barrel-shape. Flat tiles, low-profile barrel tiles, and an “S”-profile have become common. Ludowici’s sister company, Celadon, is now making a ceramic tile designed to look like natural slate (see figure 4). At $250 per square, Celadon’s clay-slate is significantly cheaper than Ludowici’s tiles, but it also comes with fewer special accessory shapes and color options, and only a 60-year warranty. While tiles used in most regions of the U.S. are made domestically, many of those used in Florida are imported from Latin America or Southern Europe, according to Rick Olsen of the National Clay Tile Manufacturers Association.
Clay is an abundant resource in most of the world. Even after more than 100 years of tile- and brick-making, there is still plenty of high-quality clay in Southeastern Ohio, where Ludowici is located, according to Crawford. Most of the clay on Ludowici’s own 150-acre site has been used up, however. Based on data from the manufacture of other vitreous clay products, unglazed clay tiles require about 2,700 Btu/lb (6,300 kJ/kg) to make. At a typical weight of 800 pounds (360 kg) per square, the embodied energy would be 22,000 Btu/ft2 (250,000 kJ/m2). Tiles are heavy, so transportation may also require significant energy unless tiles are made nearby out of local clay. Clay tiles should be very durable, so in spite of their energy intensity they may make a good choice for roofs. Keep in mind, however, that lower-end clay tiles may not be resistant to freeze-thaw damage.
Concrete tile has emerged as a cost-effective alternative to clay. They are made of Portland cement and sand. Iron oxide and other pigments are often added to impart color, though the color is prone to fading over time. The concrete mix is extruded into the tile shape and then cured to the desired strength. Freeze-thaw damage can be a concern with concrete tiles, unless they are specifically formulated to withstand it. Environmentally, concrete tile may not be ideal because it is less durable than the clay it replaces. It is also heavily reliant on cement—which accounts for 25% of the product by weight—an energy-intensive material (see EBN Vol. 2, No. 2).
Slate shingles are durable, attractive, and environmentally benign, at least in areas where the slate is quarried. The material is quarried from open pits, split to the desired thickness, cut to size, and drilled for nailing. Embodied energy required for production is limited to fossil fuels required for quarrying, shaping, and transporting the material. Roofing slate is generally available in green, gray, or reddish purple shades.
The material is so durable that there is an active market in used slate removed from buildings that are being dismantled, often after over 100 years. The Roanoke, Texas company TileSearch specializes in sourcing and selling salvaged clay tile and slate roofing. According to Melvin Mann, president of TileSearch, used slate sells for only slightly less than new. He believes that the quality of the stone used 100 years ago yielded superior product, making the old slate quite valuable.
Most fiber-cement products are made by a technique known as the Hatschek process.
In this process a slurry of cement, sand, fibers, and water is sprayed onto a belt. Then, as the water drains off, the material is pulled in layers onto a drum. Once it has reached the desired thickness and density, the sheet on the drum is further dried and then cured. Some companies cure the product in an autoclave, which applies heat and steam to speed the process, while others let it air-cure for several weeks. The air-cured product is less brittle than the autoclaved product.
Products differ as to whether the color is applied in a coating or through an integral pigment, which may extend all the way through or just be in the top layer. Pigmented products may or may not receive a protective coating.
Fiber-cement roofing products have been around for quite a while, though until recently the fiber of choice was asbestos. In fact, asbestos is still used throughout Europe because regulators are convinced that the fibers aren’t a problem unless they become airborne, and they consider that unlikely when the fibers are locked up in the tile. Until recently, most American fiber-cement products were made by European or Australian companies. These companies have reformulated their North American products to eliminate the asbestos, generally by substituting cellulosic fibers from wood chips or waste paper.
Unfortunately, the switch to cellulosic fibers has increased the susceptibility of the shingles to freeze-thaw damage, causing serious problems for some companies. FibreCem Corp. of Charlotte, North Carolina was affiliated with Eternit A.G. of Switzerland. (The Eternit group of companies is the largest manufacturer of fiber-cement products worldwide.) FibreCem advertised their product as freeze-thaw resistant (and sold it throughout the U.S.) only to discover that it wasn’t. FiberCem honored their warranty on at least one installation—the ReCraft 90 demonstration house in Missoula, Montana—but has since discontinued their operations (figure 5).
Eternit, Inc., of Blandon, Pennsylvania is importing fiber-cement slates from its Belgian parent company and claims to have no trouble with freeze-thaw damage. The company does manufacture some non-roofing products in the U.S. and is working towards domestic manufacture of the shingles, according to Todd Griesemer, product applications engineer.
James Hardie Building Products of Fontana, California is owned by an Australian company which has always used wood fibers. In fact, the U.S. plant imports its fibers from the Monterrey pine plantations of New Zealand. Hardishake™ and Hardislate™ are uncoated, but they are not sold in regions subject to freeze-thaw cycles.
Another company, Supradur Manufacturing Corp. of Rye, New York, sells a range of coated and uncoated products made at its Wind Gap, Pennsylvania facility. The company is now in Chapter 11 receivership, however, apparently due to the high cost of their investment in asbestos-free technology.
Meanwhile, several large American building product companies have gotten into the fiber-cement act. Leading the pack are producers of cedar shakes and shingles in the Pacific Northwest that are seeing their markets shrink due to fire and resource concerns. American Cemwood Corp. of Albany, Oregon is a subsidiary of MacMillan Bloedel Ltd.; and Re-Con Building Products, Inc. of Mission, British Columbia (maker of the FireFree™ line of fiber-cement roofing materials) is owned by the Clarke Group, the world’s largest manufacturer and treater of cedar shakes and shingles. Most recently Louisiana-Pacific Corp. (L-P) has jumped into the ring with its Nature Guard™ Fiber Cement Shakes, made in Red Bluff, California. This newly announced product will be available initially only on the West Coast and in the Southwest. L-P plans to release the product elsewhere sometime in 1996, once the company is more confident about its durability in cold climates.
Cedar Shakes and Shingles
The esthetic appeal of cedar shakes and shingles is attested to by the number of products designed to simulate the look.
Of the two, shakes (which are split) are more common on roofs than shingles (which are sawn—see figure 6). Although old-growth cedar heartwood is naturally decay resistant, cedar roofs require regular cleaning to prevent debris from building up in the gaps and causing rot. Cypress, redwood, and, more recently, preservative-treated southern yellow pine have also been used to make shakes and shingles.
Fire has traditionally been the main concern with cedar roofs. A new law in California effectively bans untreated cedar roofs by requiring all roofs to attain at least a class C fire rating. Cedar shakes and shingles can be chemically treated to reach a class C or even a class B rating, though some have questioned the durability of the fire retardant treatment. These treatments add substantially to the product cost, as well—15% to 25% according to Mark Rutledge, vice president of marketing for the Clarke Group. Although the chemicals they use are proprietary the Material Safety Data Sheet reveals that the solution includes a suspected carcinogen.
Environmentally, cedar has some positive features. Like other wood products, it requires relatively little energy for manufacture. In addition, the relatively high insulating value of cedar (compared with other roofing materials) makes it effective at reducing attic temperature in hot climates, according to an industry-sponsored study.
Most would argue, however, that these environmental benefits are outweighed by the negative impact of cutting cedar in the old-growth forests of the Pacific Northwest. Ecologically, cedar is an important wood to leave in the forest even after it has died, because cedar snags and submerged logs provide durable wildlife habitat. Roy Keene, a long-time forester who now heads the Public Forestry Foundation, is concerned about the cedar resource. Unlike Douglas fir, which is commonly replanted after harvest, “There has been no concerted effort to plant cedar,” Keene notes. Much cedar is exported as logs (through regulatory loopholes) or after minimal processing, and the remaining trees are under attack by root-rot, which is exacerbated by logging and road-building, according to Keene. Although shakes and shingles can be made from short lengths of wood, high-quality products do require healthy heartwood material. “The harvest of cedar is at this time nonsustainable,” Keene concludes, “I would strongly suggest that today builders should be looking to other products.”
Sheet metal roofing has traditionally been associated with agricultural buildings but is increasingly common on homes and small commercial buildings.
Products vary in thickness of the metals, type and quality of protective coating, and panel profile. Products available range in shape from flat sheets of coated steel which are formed on site to create standing seams (see figure 7), to various pre-formed sheets, to individual steel or aluminum shingles. To a small degree other metals, such as copper, stainless steel, and zinc, are also used.
Steel panels, representing the vast majority of metal roofing, are made almost exclusively at large plants that process raw iron and make the finished steel (integrated mills). These facilities rely primarily on the basic oxygen furnace for steelmaking, using about 20% recycled content (14% post-consumer). Sheet steel is made by rolling newly cast slabs, both when they are still hot and after they have cooled, to the desired thickness and welding them into long coils.
The panels are then coated with a protective layer of zinc, aluminum, or a combination of the two. Galvanized sheets use pure Zinc as a sacrificial coating, which works through galvanic reaction with the steel, resulting in a protective layer of oxidized metal. Aluminum, on the other hand, creates a true barrier and typically last longer. Most effective is a Galvalume coating, which is 45% zinc and 55% aluminum, taking advantage of the strengths of both materials. All these coatings come in various thicknesses. If the finished sheet will also be painted, a thinner metallic coating is used than if the metal will be exposed.
While steel coils are often painted at the factory in Europe and Japan, in the U.S. they are painted exclusively at separate coil-coating facilities. These specialized plants apply organic coatings to the steel, which can improve durability and provide many color options. Some paint coatings are subject to fading and chalking, however. Coatings for roofing applications are typically based on resins of polyester, siliconized polyester, or a polyvinylidene fluoride, known by the trade name Kynar 500™. The latter is the most colorfast, durable, and expensive. Warranties for steel roofing are generally direct pass-throughs from the steel mill or coil-coater, typically for 15 to 25 years. Costs for the products range from $65 per square for a thin, galvanized sheet to as much as $400 per square for a thicker sheet with Kynar-based coating.
Steel roofing can be repainted on a roof, though such field-applied coatings won’t usually last more than five to seven years. Aside from deterioration of the coating, under favorable conditions a steel roof should be quite durable. In practice, however, a service life of more than 50 years is unusual, except for the most expensive products. Steel roofing is also susceptible to dimpling from hail and is not considered a good performer in high winds, though extra fastening may take care of that problem. Fastening systems must also take into account the thermal expansion and contraction of the steel panels.
All metal roofing is energy-intensive to manufacture, and the sheet steel used for roofing contains much less recycled material than do most heavy steel members. The ease with which metal roofs can be recycled may be their greatest environmental advantage. Even the zinc coating on sheet steel is usually reclaimed, though any aluminum in the coating is not. Some toxins might be created when organic coatings are burned in an electric arc furnace—several industry experts acknowledged this might be an issue, but none knew of any relevant data.
Some aluminum roofing products, such as the Rustic Shingle from Classic Products, Inc., of Piqua, Ohio, contain 98% recycled metal. Recycled aluminum reportedly uses only 15% of the energy of virgin material.
On the Fringe
Below are several products we feel are noteworthy, even though they do not currently represent a significant share of the roofing market.
Plastic panels. Plastic roofing panels have occasionally received significant coverage in the press, especially when they are made with recycled content, such as old computer casings. We found only one recycled-content plastic currently on the market, and even this product may not always contain the advertised recycled content.
The EigerShake™ roofing panel from Eiger Building Products of Miami, Florida claims to have 52% recycled resin. A follow-up check by EBN with GE Plastics, Inc. indicated that the resin Eiger is using—GE’s Noryl PX1718—does not contain any recycled content. After repeated phone calls, company president Douglas Hudson finally contacted EBN to explain that the product is approved using both the PX resin and a recycled MX resin, “in case the MX resin should be in short supply.” There appears to be no guarantee that product purchased from Eiger does in fact contain recycled plastic. In addition to Eiger, Nelco Engineering, Inc. of Maryville, Tennessee makes panels from a (nonrecycled) Noryl resin. Several entrepreneurs have other products in the works, but we found none that are market-ready.
Recycled or otherwise, many doubt that plastic panels make sense as a roofing material. One high-profile installation of recycled-content plastic panels was a product made by Nailite International, used on a McDonald’s restaurant in Chicago in 1991. Nailite President and CEO Bill Eagle reports that the product used was strictly a prototype that never went on the market. Eagle, an executive with a long history in the roofing industry, pulled Nailite out of the plastic roofing market shortly thereafter. “Roofing is a very demanding application,” he says. “I’m not confident that plastic, especially painted plastic, can be depended on for more than ten years.”
Aside from being energy-intensive to make and entirely fossil-fuel derived, plastic roofing products must contain additives to protect them against UV radiation and to increase their fire resistance. Environmentally they appear to make little sense.
Used tires. At least two backyard entrepreneurs are trying to capitalize on the tire glut by cutting off the sidewalls and using the tread as roofing tiles. Richard Moore, a roofer in Squamish, British Columbia has patented this system and covered about 20 roofs to date. His company, Moore Enviro Systems, uses three variations on the technique, costing between $1.50 and $2.00 per square foot (0.093 m2) installed. Their product has a class B fire rating and is presently being tested for other characteristics.
Another company, Tread Mill Inc. of Williams, Oregon, has generated a lot of local interest but isn’t as far along in the process as Moore. In principle this approach appears feasible if the esthetic and possible fire concerns can be overcome. Environmentally it certainly looks like a win-win situation.
Solar shingles. One elegant strategy for integrating solar electricity generation is with PV shingles (see figure 8).
Solarex Corporation supplied PV tiles to Misawa Homes in Japan last year. The Swiss Atlantis Energie A.G. is marketing PV shingles in the U.S. through its subsidiary, Atlantis Energy, Inc. of Grass Valley, California. Another subsidiary, Solar Building Systems, will begin making the shingles in Virginia this fall.
PV shingles are currently more expensive than roof-mounted PV panels, even when you account for the savings in roofing. If current trends continue, however, the price may eventually come down to a more competitive level. In addition to the environmental benefit of pollution-free electricity, generating the power on-site reduces the need for transmission facilities.
Over the years a remarkable diversity of materials has been used for roofing, with varying degrees of success. As with many material choices, the designer or specifier is frequently faced with a trade-off between cost and quality in roofing materials. At the low end of the cost spectrum the options are quite limited, while a higher investment opens up a wide range of options, including both traditional and newly developed materials. As with any material, environmental considerations are important, but they should not come at the expense of basic functionality. This concern is especially apparent with roofing, which is replaced so often. The recommendations below may help guide your choices.
•The low end of any product line is more likely to have defects and fail prematurely than products which afford the manufacturers slightly higher margins. This is especially true with the inexpensive asphalt roofing products, which amount to a disposable roofing system that is difficult to dispose of!
•Fiber cement products can be an attractive option, as they use much less energy-intensive cement than concrete tiles and are otherwise resource-efficient. Review the options carefully in freeze-thaw prone regions, however, and beware of untested new products.
•In regions where it is quarried, slate offers a durable and attractive, albeit expensive, option.
•In regions where clay tile is produced from local clay, this may be a good choice. In cold climates look for a low-water-absorption rating to reduce the potential for freeze-thaw damage.
•Wood shakes and shingles come from a resource base that is theoretically renewable but in practices is currently quite limited. They also require regular maintenance and may be a fire hazard. They should probably be avoided unless convincing (independently certified) evidence is available that the shingles are produced from responsibly managed forests.
•In hot climates, consider using a highly reflective roofing material, such as a light-colored metal roof, to reduce solar gain through the roof. This function is especially significant when reroofing buildings that have minimal attic insulation. Light-colored asphalt shingles are only marginally better in this respect than dark ones (see EBN Vol. 2, No. 5). White-painted metal roofs are especially good, while bare metal roofs tend to lose their reflective gloss quite quickly.
•On steel roofs that are not subject to extreme moisture and corrosive salt air, high-quality, unpainted coatings may be the best choice because they are not subject to chalking and fading. Where a paint coating is desirable, white is a good choice because chalking a fading are not noticeable.
•If roof-integrated PV or solar hot water is not currently feasible, consider facilitating the future installation of such a system with appropriate orientation and exposure, conduits to the attic, and an interim roof surface that can easily be recycled.
•Ensure that the entire roof system, not just the main surface, is designed and assembled for durability. Flashing details where different planes meet and at penetrations are particularly important.
•You can improve a roof’s long-term performance by providing maintenance guidelines for the building owner and/or manager.