The type of roofing you choose can have a serious impact on your health and on the environment. Sloped roofing materials, such as asphalt-based rolled roofing and shingles, will offgas toxins when heated by the sun. Flat roofing materials, such as tar and gravel, will also continually offgas when heated by the sun, emitting known carcinogens such as VOCs from asphalt, including benzene, polynuclear aromatics, toluene, and xylene. Although roofing materials are located outside the living space, odors can enter the home through doors, windows, and vents. Since most people aren't in a position to move out for several weeks when their roof requires replacement, they will be exposed to high levels of toxic fumes every time the roof is replaced or repaired.
Seventy-eight-percent of total annual roofing dollars spent in the US is spent on re-roofing. According to some studies, re-roofing can be necessary for common roofing types after only 12 years, especially in higher altitude climates, which have greater exposure to ultraviolet rays. This isn't only an expensive hassle, but it also sends used roofing materials to landfills, where the polluting contents continue to offgas and leach into the soil and groundwater.
Unfortunately, re-roofing your house is often a necessity. You’ll know when you need a new one: the roof leaks, the shingles start to curl, or icicles will hang from the roof. Even if you’re lucky enough not to have these problems, a new roof with good air sealing, insulation, and ventilation will save energy and make your house more comfortable. Many unhealthy and persistent mold and mildew infestations begin with an undetected roof leak. No type of roofing installation is foolproof, but the use of high quality roofing materials and skilled installers will reduce the risk of leakage. Moreover, roofing replacements give you a chance to work on areas of the house that are usually impossible to get to. Here are some green alternatives to traditional roofing that help make re-roofing your home a healthy long-term investment for you and our environment:
Legend: $ = cost effectiveness; EE = energy efficiency; RC = resource conservation; HB = health benefit
Consider the System as a Whole - $
• In new construction, choice of roofing materials should be integral with other decisions about the building. The roof is your main defense against water leakage in your house. Good roofing is often degraded when budgets are tight and compromises are made. You want a roof that will last at least as long as your mortgage because long-lasting roofing protects your home and your investment.
• Recommendation: Early in the decision-making process, figure out your roofing and how it will integrate with the rest of the house. Make sure the roof framing structure is designed to bear the weight of the product you choose.
Calculate How Much Roofing You’ll Need - $
• Roofs are measured in 100-square-foot areas, or “squares.” Three bundles of three-tab shingles typically equal one square; laminates come in four bundles per square. It’s a good idea to calculate beforehand how much roofing material you’ll need so that you’ll have an easier time comparing bids from contractors.
• Recommendation: To gauge how much roofing material you’ll need, multiply the overall length and width of each roof section to determine its area. Add ten % to allow for waste, then divide by 100 to determine how many squares you’ll need. If the roof is new or you’re having the old shingles removed, you’ll need an underlayment (roofing felt) to create a moisture barrier for the wood sheathing and rafters underneath. The sheathing may have to be replaced in severely damaged areas. You may also have to install an “ice-and-water shield” along the eaves and the valleys where two wings of the roof intersect. New drip edges and metal flashing are often needed around pipes, chimneys, and the like.
Avoid Adhesives - HB
• Adhesives used in roofing applications can emit harmful VOCs. Solvent based adhesives affect the respiratory and central nervous systems, as well as organs like your liver and kidney. They are especially toxic during application and curing (drying) periods. Water-based adhesives are better because they only release water vapor as they dry, but they aren't necessarily 100 % safe. Other components in water-based adhesives, such as resins, biocides, other solvents, and even some natural ingredients, can be irritants or toxins. Mechanical fastening eliminates the need for VOC-offgassing adhesive materials. In addition, the membrane can be easily removed and recycled when it fails or when the roof needs to be modified.
• Recommendation: Use mechanical fastening, a range of processes that utilizes a variety of fasteners including nails, nuts and bolts, strews, and rivets, to assemble materials without heating or adhesives. If mechanical fastening is unavailable, use water-based adhesives.
Provide a Light-colored or Reflective Roof - EE
• Dark roofing materials absorb heat and make the house warmer in the summer, whereas light-colored roofing reflects heat away from the building. Higher solar reflectance can be achieved with lighter colored roofing materials such as shingles, tiles, and white-reflective membranes and coatings on flat roofs. Unless the building has a highly insulated roof, it's generally advisable to provide a reflective roof surface. Reflective roofs help reduce “the heat island effect,” a phenomena in which heat-absorbing buildings can increase the outside air temperature in urban areas by two to eight degrees Fahrenheit. Light-colored roofing also reduces heat buildup through the roof. As a result, if you have air conditioning ducts running through the attic, the ducts will stay cooler. Considering that air conditioning is the most energy-intensive appliance in the house, the energy savings are significant! Light-colored roofing can also last longer because it does not thermally expand and contract as much as darker colors.
• Recommendation: Use a roofing material with as high a reflectance as possible.
Install Radiant Barriers - EE
• Reflect heat away from your home by installing a radiant barrier on the underside of your roof. A radiant barrier is simply a sheet of aluminum foil with paper backing, or metalized mylar sheet material. When installed correctly, a radiant barrier can reduce heat gains through your ceiling by about 95 % . They are particularly helpful if you have air conditioning ducts running through your attic, because the lower attic temperature keeps the ducts cooler. In fact, some homeowners save more from cooler ducts than from the benefits of keeping the ceiling cool.
Recommendation: Install radiant barriers by stapling them to the attic rafters don't staple them to attic floor joists where dust collects on them more quickly. Alternatively, use laminated foil-backed OSB for new roof construction, reflective side down.
Use Recycled-content Asphalt Shingles – EE, RC
• Asphalt shingles are among the most disposed-of building materials. Recycled-content asphalt shingles, on the other hand, contain recycled waste paper and /or use reclaimed material slag in their aggregate surface, thereby reducing the waste of raw materials during the roofing process.
• Recommendation: Install recycled-content asphalt shingles rather than traditional asphalt shingles.
Table of Reflectance of Roof Materials:
Install Slate Roofing - RC
• Slate is minimally processed cut or split rock. It is expensive, but it creates a very distinctive look and is incredibly durable. Not only does it have a good fire rating, but properly installed slate roofs can last 100 years or, more with only minor maintenance. Slate is considered a safe material that can be easily reclaimed and reused on new building projects.
• Recommendation: Consider slate roofing if it's quarried near your home. Adequately strong roof structures must be built to withstand this heavy material. Keep in mind that slate requires skill to install and repair.
Install Concrete Tile Roofing - RC
• Concrete tile is a waterproof material that may be coated or glazed for special effects. Like all concrete products, concrete tiles contain energy- intensive Portland cement. However, we support concrete tiles as a good green alternative to asphalt shingles because of their durability; low-to-no toxicity, easy maintenance, and excellent fire rating.
• Recommendation: Consider concrete tile if it's manufactured in your region, since it's heavy and difficult to transport. Keep in mind that larger structural systems will be required to support its extreme weight. Concrete tiles depend on rapid water runoff and will not hold up under the standing water conditions common with low-sloped roofs. Also note that cement roofing may shatter in high hail-prone areas.
Install Clay Roofing – RC, HB
• Clay tiles are made from slabs of clay and lined with a glazed or unglazed finish. This natural, traditional roofing material comes in attractive colors and textures that improve with age. Although clay is more expensive than many roofing materials, it's a durable, fireproof material with no negative health effects. New clay roof tiles can be made to, match old tiles, making them the ideal choice for refurbishment as well as new roofing in areas where it's architecturally appropriate.
• Recommendation: Consider using clay if it's quarried in your region. If you are installing clay tiles in cold climates, note that low-water absorption ratings minimize the potential for freeze-thaw damage. Clay tiles are heavy, therefore some rafters may need to be reinforced. Keep in mind that clay roofing may shatter in high hail-prone areas.
Install Lead-free Metal Roofing – EE, HB
Use metal roofing made from aluminum, copper, or steel. The components come in many sizes and shapes, including panels, shingles, shakes, and tiles. Some products contain up to 100 % recycled material, and most products can easily be recycled. Metal roofing is easy to install, and is fireproof, lightweight, long-lasting and recyclable. It is available in a wide range of shapes, colors and patterns. Metal is the most favorable roofing material used in rainwater catchment systems. In northern climates, snow readily slides off metal roofs, thereby avoiding the damage caused by ice dams. Unlike all other roofing materials, metal roofs also provide added shear value or rigidity to the roof. Metal roofs don't radiate as much unwanted heat into the attic as asphalt shingles, because the metal is thin and does not have heat holding capacity. Using a white painted or galvanized finish will further reflect heat away from the roof and attic.
Recommendation: Use high- quality unpainted coatings on metal roofs that aren't subject to extreme moisture and corrosive salt air. Avoid roofing where lead is used in the alloy or coating. (See “Lead” in Section 5.) Use of different metals for roofing, flashing, and fastening isn't recommended; in the presence of water, different metals in con tact with each other are susceptible to galvanic corrosion. Try to use roofing profiles (fastening mechanisms) with hidden screws or clips to avoid penetrating the metal on the surface and inviting future leaks. Keep in mind that metal roofs can be somewhat loud during rainstorms, therefore occupants should be comfortable with this form of “white noise.”
Install Fiber-cement Composite Roofing - RC
• Fiber-cement is made of Portland cement, sand, clay, and wood fiber. The product typically carries a 50 year warranty. Fiber-cement composite roofing is durable, fireproof and recyclable.
• Recommendations: This roofing can be readily used on standard roof structures. Fiber-cement composite slates or shakes aren't recommended in northern regions or at higher altitudes because they don't perform well in freeze-thaw climates or in hail-prone areas.
Install Recycled-content Plastic/Rubber Shingles - RC
• Plastic shingles are made from recycled materials like industrial rubber, used tires, and plastic — and the shingles themselves can be recycled at the end of their life. Although the long-term effects of UV light and the expansion and contraction of plastic materials remain unknown, many of these products have a 50-year warranty. They are also sound-absorbent and hail-proof.
• Recommendation: Use plastic shingles in place of traditional asphalt shingles. Some varieties can be installed just like clay or slate tiles; other types look like rough cedar shakes.
Install a Steep Slope Roof with Sizable Overhang – RC, EE
Water will puddle and linger on poorly constructed flat roofing. As a result, flat roofs have a high leakage rate that may lead to devastating mold problems. A steep slope roof has a “pitched” roof line that prevents water from puddling on your roof. The roof overhang plays an important role in protecting the walls and foundations from water damage by directing water away from your home. Overhangs can be sized to suit the solar conditions in your region, providing shade in the summer while allowing maximum heat entry in the winter. Non-toxic roof materials are readily available and are standard products for sloped roof construction, whereas they are an exception in flat or low-sloped residential roof construction.
• Recommendation: Install a roof with a minimum 3/12 pitch. This fraction refers to the rise/run of the roof.
Harvest Rainwater – RC, $
• Whenever it rains, naturally distilled water falls on roof tops, is guided into gutters, and is quickly sent into sewers to be combined with human and industrial waste and “taken away” at great expense. Without gutters it will fall off the roof, damage your walls and foundation, wash away your landscape and soil, and possibly run onto the street and cause flooding. However, rainwater can be diverted for use onsite before it's lost along with domestic waste. Rainwater is soft and pure and requires no treatment; rainwater recovery works well even in drought-prone areas and can often reduce your water bills. In addition, water-supply and storm water drains become unnecessary. In fire-prone areas, you might even position big containers at a height that can gravity-feed a hose, thereby reducing your fire insurance premiums.
Recommendation: Install cistern tanks that collect rainwater. This pure water can be used for landscape watering. You might also install simple rainwater “buckets” to collect rainwater from gutters for watering.
Consider Green Roofs - RC
Green roofs, as the name implies, are planted with vegetation. Also known as “living roofs,” these are protected-membrane roofs with soil and plantings (as well as insulation) installed above the membrane. These systems are encouraged and even subsidized in Europe because they reduce flooding risks and cooling needs. They can detain over half the rainwater from a typical storm, reducing the often-high loads placed on sewer systems after a rainfall. In addition, a green roof can be a wonderful architectural element that absorbs carbon dioxide (see “Global Climate Change”), and helps to reduce building heat gain and urban heat islands.
Recommendation: Install a green “living” roof in place of a traditional low-slope or flat roof. A green roof includes insulation, drainage, geotextile, soil, and vegetation layers. These multilayered green roof systems are thicker and heavier than conventional roofs and are often used for gardens, therefore the roof structure needs to be engineered to accommodate the increased weight of the roof and people walking on it.
Install 40- to 50-year Composition Roofing - RC
• Composition asphalt/fiberglass roof shingles typically come in 15- to 50-year life spans. Although the 15-year warranty roofs tend to be less expensive, they will also have to be replaced more often. This costs more in the long-run and adds to manufacturing and landfill pollution.
• Recommendations: Use 50-year composition roofing anytime your roof needs to be replaced.
Consider PV Shingles and Roofing Tiles - $, EE, RC
• These new roofing systems are coated with a film that converts sunlight into electricity. The shingles or tiles snap together, and the current flows at the edge of the roof. The shingles look a lot like traditional roofing, and any good roofer can install them. After the roofer installs the tiles, an electrician connects the roof system with the electrical system. Each 100 square feet of PV roof generates about one kilowatt of electricity. PV can be used as a means to decrease reliance on conventional power plants that contribute to air pollution. PV can be cost effective in areas that require night lighting such as outdoor lights. (See “Photovoltaic (PV) Energy”
• Recommendation: Use PV shingles instead of traditional roofing. Be sure that the roof is oriented to the south or southwest. The components for a utility-tied system typically include panels, a power relay center, and an inverter. An alternative installation would be self-contained systems (battery included) for outside lighting, security lighting, or walkway illumination.
FYI: Heat island effect. A phenomena in which heat-absorbing buildings can increase the outside air temperature in urban areas by 2 to 8 degrees Fahrenheit (1 to 4 degrees Celsius).