At the most basic level, a roof protects you from the elements. And the greenest roof is the roof that lasts the longest. But new kinds of roofs can do more than keep you out of the rain and snow. Some will keep your house cooler, making you feel more comfortable and giving your air conditioner a break. Some provide wildlife habitat, and others collect rainwater you can use to water your garden. Others perform the amazing feat of harvesting sunlight to power your house and heat your water.
The right material for your climate. If you live in a place with hot and sunny weather, choose a “cool roof” made with products designed to reflect the sun’s heat. Energy Star-qualified cool roof products can lower the roof’s surface temperature by as much as 100° F. and reduce the energy you use for air conditioning by 10% to 15%. Earlier cool roofs were white or very light colored, which didn’t work with every architectural style. But today’s cool roof products are available in wide range of colors and materials. Another benefit is that they don’t expand and contract in the sun as much as other roofing materials and so are likely to hold up longer.
Planet-friendly materials. Which natural resources and how much energy went into making the product? How far did it have to travel to reach you? (Products that come from great distances typically use more transportation energy than locally made products.)
Recycled materials. Several companies now offer slate or cedar look-alikes that are really made from recycled plastic or automobile-tire rubber. These products are too new to have proven durability, but some manufacturers offer 40- or 50-year warranties. Pricing is comparable to wood shingles and much less than real slate.
Long warranties. Choose products that can last 40 or 50 years. They’ll cost more than the lower-grade products, but they’ll hold up better.
Other Considerations
A newfangled take on the old sod roof, a vegetated “green roof” is a multilayered system of insulation, waterproofing, root barriers, drainage, lightweight soil, and, of course, plants. Green roofs are expensive to install (about $8 a square foot, compared with $1.25 a square foot for conventional roofs) and generally work only on low slopes. But they can offer tremendous benefits. They replace barren rooftops with grasses, succulents, wildflowers, or herbs–a vibrant habitat for birds, butterflies, and other critters. They insulate buildings, reducing heating and cooling costs. They extend the lives of roofs by protecting them from UV rays and thermal expansion. They reduce the heat-island effect and filter pollutants from the air and rainwater. And of course they look beautiful, too.
With the right roofing materials, you can also collect rainwater from your roof to water your garden. Rainwater harvesting systems range from basic barrels under a downspout to huge underground tanks complete with pumps to get water to your plants. Good roofing options for rainwater harvesting include clay or cement tile, some metals, and slate. Avoid anything that may leach poisons into the rainwater, such as asphalt or tar. With wood, leaching can occur from mold or algae growing on the wood, or from the preservatives and fire retardants used to treat it. The jury is still out on leaching from recycled-plastic shingles.
To help you assess the more conventional roofing options, here’s an introduction to their pros and cons.
Asphalt shingles are the most common roofing material. They top two-thirds of U.S. homes, and millions of tons of them wind up in landfills each year. They consist of a fiberglass or paper mat coated with asphalt (a petroleum-based product) and topped with mineral granules that provide UV protection. Lower-grade products cost less, but last only 15 or 20 years. The need for frequent replacement takes its toll on the environment. If you do choose asphalt shingles, choose a heavier, thicker, premium-grade product with a 40- or 50-year warranty.
Concrete and clay tiles are popular in some parts of the country. Clay tiles are made from clay, an abundant though nonrenewable resource. The main environmental issue is the energy necessary to fire and transport them. Often fashioned to look like clay, concrete tiles are cheaper. They contain about 25% portland cement, an energy-intensive material to manufacture, but are otherwise relatively environmentally benign. Clay and concrete tiles are heavy, so it’s a good idea to seek out locally made products to minimize the dollar and energy cost of hauling them long distances. Clay and concrete tiles are durable and fireproof but they can shatter in severe hailstorms. If you live in a cold climate, make sure the tiles you choose are rated to withstand freeze-thaw cycles.
Fiber-cement shingles are made of cement mixed with wood fiber; they used to contain asbestos but no longer do. They’re durable and fireproof, but may shatter in hailstorms. If you live in a cold climate, choose a product that’s rated to withstand freeze-thaw cycles.
Wood shinglesand shakes are a traditional roofing material in some parts of the country but they can be expensive. (Shingles are sawn from logs and have a smoother finish; shakes are split from logs and look more rustic.) Some products are treated with preservatives or fire retardants–the latter being a requirement for wood roofs in some regions. These roofs will last longer, but they may leach chemicals into waterways. Premium grades are also tougher, but more likely to come from old-growth trees. You can get around this problem by choosing Forest Stewardship Council (FSC)-certified shingles and shakes.
Metal roofs, which come in panels, shingles, and tiles, are lightweight, strong, durable, and fire resistant. Aluminum, steel, and copper are the most common metals used, and although manufacturing them takes a lot of energy, many contain high recycled content and most are recyclable.
Slate tiles can last 100 years or more. If they’re ever removed they can be reused for roofs, flooring, or countertops. Slate is minimally processed and relatively environmentally benign. For the greenest option, choose salvaged slate. But if you’re buying it new, look for stone quarried in your part of the country to minimize transportation energy.
The most common and least expensive material for flat roofs is built-up tar and gravel roofing. It’s installed by putting down layers of roofing felt (actually sheets of fiberglass or paper but known in the building industry as felt) coated with hot asphalt or bitumen–a tar-like material made from petroleum or coal. The hot asphalt and bitumen create quite a stink when they are being applied. The top layer is spread with gravel for added UV protection. When newer tar-and-gravel roofs heat up in the sun, they give off VOCs. While most of these VOCs wind up in the outside air, some may make their way into your house through windows and vents. Tar-and-gravel roofs typically have shorter life spans than most other roofing materials–only about 12 years on average.
Benefits…
…to you
A durable, high quality roof protects you and your home from the elements. Specialty roofs can also generate power, harvest water, or make your home warmer in winter and cooler in summer, harvest water, and generate power.
…to your wallet
The 10% to 15% that a reflective roof can save you on air conditioning costs is nothing to sniff at if you live in hot climate. In a city like Phoenix, for instance, you could easily save $150 a year with a 1,000-square-foot “cool” roof.
…to the Earth
Durable roofs require less frequent replacement. That means less greenhouse gas is emitted, less nonrenewable material is wrested from the Earth, and a lot less waste piles up in landfills. Roofing materials with recycled content keep even more valuable resources out of the waste heap. With widespread use, “cool” roofing products could lead to cooler cities, reducing the need for air conditioning in buildings and cars, and decreasing smog and heat- and smog-related health problems.
Common Mistakes
Cutting corners. A lower-quality roof may cost you less upfront, but can be costly when you have to replace it or if it fails and allows water into your home.
Procrastination. If your roof leaks, don’t delay in getting it repaired. Moisture intrusion can lead to mold and rot, which may cause health problems for your family and could lead to serious structural problems for the building.
Getting Started
If you’re considering a green roof, be sure to hire an installer with extensive experience and get an excellent warranty: the failure of a green roof could be very expensive to fix. Green roofs do require some maintenance, especially until the plants are well established. In fire-prone regions, local building codes may require the roof to be irrigated. Get advice from a structural engineer about whether your house can bear the added weight of a green roof.
For general advice on what questions to ask contractors and other tradespeople, see our “What to Ask Your Contractor” article.
Use our Green Directory to find a green roof contractor in your area.
