Whether you're tackling a reroofing project yourself or hiring a roofing professional, it's worth your while to get familiar with today's environmentally friendly roofing options. A good roof will hold up for decades, protect your home from water damage, keep your repair and replacement costs in check, and reduce your heating and cooling bills. Make it a priority to choose a durable roofing material and be sure it's installed properly.
If you are building a new home or an addition, make sure that the new roofs includes adequate overhangs and gutters to help keep rainwater off the building. If your air conditioning bills are high or your house gets uncomfortably hot in the summer, consider radiant barriers and cool roof products.
Some roofs do a lot more than protect buildings from the elements. They can also provide valuable real estate for locating solar panels or a beautiful roof garden.
Overhangs and gutters
Overhangs and gutters reduce maintenance and repair costs by helping keep water off of the siding, windows and doors, thereby reducing the likelihood that rot and mold will develop. Gutters provide a pathway for water to flow off of the roof without hitting the walls, splashing back onto the foundation and siding, dripping onto people and eroding the landscape.
Overhangs can also shade windows, helping keep the home comfortable and reducing air conditioning costs. And overhangs can provide protection from the sun's harsh UV rays, which can degrade building materials and furnishings.
Ideally, a home's entire roof should be built with at least a 16-inch overhang with gutters. When building an addition or substantially remodeling areas of the house, be sure to include adequate overhangs with gutters on the new sections of the roof. Consider adding deeper overhangs where needed to shade walls and windows to provide cooling during summer.
Instead of draining gutters into the sewer system, drain them at least 24 inches from the building and into a rainwater cistern. You can use the stored water to irrigate your landscaping. Or drain the gutters toward adjacent landscaped areas that are graded to receive the excess water; this will allow the rainwater to water vegetation and recharge groundwater. Check with the local building department for applicable codes.
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Durable and noncombustible roofing materials
When it comes time to reroof your home, choose a durable material. Durable roofing materials are better able to withstand the elements, including the sun's heat and ultraviolet light. Short-lived roofing materials result in more waste going to landfills and more money spent on roof replacement. In extreme cases, early failure of a roofing material can result in water damage to the home.
It's important to check the fire rating and warranty period of any roofing product. Avoid shakes and shingles made from cedar and other woods. These can be a fire hazard. They also tend to have a shorter life span than other roofing materials and they are high maintenance. If you must have wood shakes or shingles, choose a product that has been certified as sustainably harvested by the Forest Stewardship Council (FSC).
There are many options for durable roofing products:
Asphalt composition shingles come in various quality levels, designated by the product's life expectancy. Twenty- to fifty-year shingles are available. Products with 40- to 50-year ratings are superior because of better backing materials and asphalt coatings.
Asphalt does have environmental downsides: it is made with nonrenewable petroleum products, and asphalt shingle recycling is currently not common practice. Asphalt composition shingles make up a large volume of the building materials that wind up in landfills. Some manufacturers offer asphalt shingles with recycled content. Rainwater runoff from an asphalt composition shingle roof is not safe to drink and can only be collected for nonpotable uses.
- Cast-concrete tiles are fire resistant and can look very similar to slate or tile roofing. Don't install cast-concrete tiles in cold climates because hail and freeze-thaw cycles can permanently damage them. Cast-concrete tiles require extra structural work to support them as they are heavier than other roof options.
- Clay tiles are a popular, durable option in California. Because of their shape, air flows around them, which creates a cooling effect for the building. However, clay tile is expensive, and does not provide a good surface for installing solar panels. Hail can shatter clay tile so it is not advised in hail-prone climates.
- Fiber-cement composite roofing is made of portland cement, sand, clay and wood fiber. It is durable and fireproof. Fiber-cement composite tiles or shakes are not recommended in cold climates or high altitudes because they do not perform well in freeze-thaw or hail-prone environments. Fiber-cement roofing is expensive to replace and cannot be walked on.
- Synthetic tiles are a composite roofing material made of recycled rubber, plastics and fillers such as wood fibers. They are fireproof, lightweight and very durable. These tiles come in many forms and can look like slate, wood shakes or shingles.
- Liquid-applied products are white and can be applied to traditional asphalt cap sheets, modified bitumen and other substrates. Products include elastomeric coatings, polyurethane coatings, acrylic coatings and paint (on metal or concrete).
- Metal roof choices include copper, steel and aluminum. Metal roofs are fireproof, lightweight and can last much longer than asphalt shingles, but they can cost more than other roofing options. Metal roofs come in varying thicknesses and styles including panels, shingles, shakes and tiles. Choose a lead-free option made with recycled content. Most steel roofs can be recycled. Rainwater catchment systems work very well on metal roofs. Snow can easily slide off of metal roofs, which helps prevent damage caused by ice buildup. Also, it is possible to integrate certain photovoltaic systems with a standing seam metal roof by either clipping panels directly to the ridges or laying thin film laminates between the ridges.
- Single-ply membranes are rolls of smooth, white plastic materials that are applied over the finish roof. The seams are welded to create a continuous heat and moisture barrier. Single-ply membrane materials include polyvinyl chloride (PVC), chlorinated polyethylene (CPE), chlorosulfonated polyethylene (CPSE), ethylene propylene diene monomer (EPDM) and thermoplastic polyolefin (TPO).
From a materials perspective, these plastic products may not be the greenest option: they are made from fossil fuels and there is no recycling infrastructure to take back products at the end of their life. Most end up in landfills or are incinerated, which creates a host of environmental toxins. When choosing a roofing material, however, it is important to balance the energy savings from reducing air-conditioning loads (or eliminating air conditioning) against the material's impact.
- Slate roofing shingles, which are cut or split from slate, are relatively environmentally benign to produce. Properly installed slate roofs can last over 100 years with only periodic maintenance. Slate traditionally comes from the mid-Atlantic and northeastern states and Europe, but today the majority comes from China, Africa or Brazil, so for buildings in California, the transportation energy may offset slate's other environmental benefits. Slate roofing can be recovered from older local buildings and reused, thereby reducing transportation impacts.
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Radiant barriers are thin reflective sheet materials (usually made of aluminum) used to reduce attic temperatures, reduce heat gain in duct work, and reduce 90% or more of the heat that the roof deck radiates into the home.
Radiant barriers are effective at reducing summertime attic temperatures and can significantly reduce air conditioning costs. They are not very effective at reducing heat loss through the attic in the winter months (insulation does a better job of reducing heat loss).
To be effective, radiant barriers must be open to air on at least one side. When installing a radiant barrier in an existing attic, the product is typically installed at the roof rafters, with the foil facing toward the interior of the attic. In reroofing situations or when building an addition with a new roof, you can use a roof sheathing product such as oriented strand board (OSB) that is laminated at the factory with the radiant barrier foil. The sheathing product must be installed with the foil facing the attic interior.
The roof generally receives more direct sunlight than any other part of the building. Dark roof surfaces absorb sunlight and reradiate it as heat to the attic and to the surrounding air. This heat gain warms any heating and cooling ducts that are in the attic. It also heats up rooms adjacent to the attic, and shortens the roofing material's life. What's more, it raises outside air temperatures, a phenomenon known as the urban heat island effect.
Cool roofing materials keep rooftop temperatures in check by reflecting a significant portion of the sun's rays away from the roof (this characteristic is known as high solar reflectance or high albedo). Cool roofing materials also reduce the amount of heat stored by the roof (a characteristic known as high emissivity).
Installing a cool roof material that is rated high in reflectivity and emissivity will reduce the amount of heat that is driven through the roof and into the attic. Cool roof products come in many colors and many materials, including metal, single-ply membrane and asphalt shingles. Also, cool roof coating products are available that can be painted over certain existing roofing materials.
Keep in mind that a white roof is not necessarily a cool roof. White surfaces can get quite hot if they have low emissivity. White sand beaches, for example, are highly reflective but store heat and can get very hot.
For more information about cool roofs, go to the Cool Roof Rating Council's website, www.coolroofs.org.
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Green roofs also go by the names of vegetated roofs or living roofs. They consist of vegetation planted in a lightweight planting medium that's installed on top of a waterproof roofing membrane. Green roofs are still relatively uncommon on homes, but they have many benefits, including:
- Keeping the building cooler, thereby reducing air conditioning energy use and associated greenhouse gas emissions
- Protecting the underlying roof membrane from UV light and extreme temperature and weather conditions
- Providing sound insulation from outdoor noise
- Creating beauty and, in some cases, outdoor recreation and food production space
- Reducing rainwater runoff to stormwater and sewage systems
- Creating habitat for birds, butterflies and other wildlife
Green roofs can be difficult and expensive to install on existing roofs that weren't originally designed to accommodate the added weight, moisture and traffic. If you are considering putting a green roof on an existing home, a roof assessment will be necessary to evaluate the existing roof's design, functions, conditions, strength and pitch. Consult a structural engineer, green roof consultant or landscape architect, and green roof substrate manufacturers before installing a green roof.
For more information about green roofs, go to www.greenroofs.com.
More roofing tips
- Plant shade trees. The sun's rays beating on the roof can really heat up a house and drive up cooling costs. Good insulation, a radiant barrier in the attic, and reflective roofing materials are all excellent strategies for blocking heat. An even lower tech option is shade trees. Plant them where they will cast summertime shade on the roof when they reach maturity. Keep shade off of roof areas where solar panels may be located now or in the future.
- Flash it. Proper flashing details help increase the roof and building life. Read our GreenPointer on Moisture and Pest Control for information about flashing.
- Make room for solar. If you are reroofing, building an addition or doing a major remodeling project, look for opportunities to add solar electric or solar hot water panels to the roof. Even if you don't plan to add solar right away, reserving roof space for future panels can be a smart move. Read more in our GreenPointer on Renewable Energy.
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