What Should I Put On My Roof?

A Reader Writes The Green Guide:

I would like to know about eco-safe roofing tiles. How about clay? Which tiles are going to last the longest and can also be used in a rain collection system? Also, are there complete photovoltaic roofing systems where the photocells are built into a 30-year (at least) roof?

Which is more environmentally friendly after installation, (i) metal "painted" roof, or (ii) asphalt shingles?

The Green Guide Responds:

Roofing presents a big problem to the homeowner for two very simple reasons: it's expensive and it has to be replaced quite often. According to BuildingGreen.com, 78 percent of the money spent on roofing is actually spent on re-roofing. And, says Paul Novack of Environmental Construction Outfitters, there isn't much environmentally advanced roofing out there. However, some materials are certainly better than others. It's best to make the correct choice from the beginning, rather than paying later in leaks and dollars.

Also, the Department of Energy and Environmental Protection Agency's Energy Star program evaluates roofing products according to relative energy savings. All products with the Energy Star label have been tested new and after 3 years of use. Always look for the DOE rating and EnergyStar label when choosing roofing products.

Materials

Clay is a good choice for your roof, because it's abundant and durable, though if you live in a cold climate, make sure the tiles you buy are freeze-resistant—look for the lowest percentage of water-absorption possible. BuildingGreen mentions Ludowici tile as particularly good in cold, if also one of the most expensive tiles on the market, $300 to $1,200 per square foot. Perhaps to make up for the price tag, the company offers a 75-year warranty. Slate, too, is a good choice. Novack likes it because it lasts "forever" even if it can be hard to install; he also likes it for rain collection. Environmentally speaking, slate's a better choice if you live near a quarry--its weight means the fossil fuel costs of transport can be high. But it's so durable that even used slate will serve you well; do a web search on "salvaged slate" to find a supplier in your area. White-painted metal can be a good choice in a hot climate: heat will be reflected, and you can cut air-conditioning costs by up to 40 percent. However, weather conditions can cut the lifespan of a metal roof to under 50 years. Novack also likes rubber tile, which is often designed to look like slate. EcoStar offers rubber roof tiles with a 50-year warranty.

Asphalt is probably the most problematic common roofing material. Though it's cheap, it's often shoddy, and when replacement costs--and the environmental costs of all that asphalt—are figured in, it's not a good choice for your roof, according to BuildingGreen. Organic asphalt is not an especially better choice, as it requires more asphalt in its manufacture. Further, asphalt can fume unpleasantly on hot days; Novack says that he lays down foil insulation to isolate asphalt tiles before installation.

Solar shingles are more expensive than roof-mounted solar panels, says BuildingGreen. Still, solar roofing is worth looking into, and help is out there. The Million Solar Roofs initiative (www.millionsolarroofs.org) is, as the name implies, trying to get one million homes partially solar-powered by 2010; it was started by the Department of Energy in 1997. Its site has information on seminars, various financial incentives, and other resources. The July/August issue of Solar Today has a cover story on the initiative: at the end of 2003, 229,000 solar roofs had been counted, more than a quarter of the 2010 goal. Solar roofing companies normally promise a lifespan approaching 30 years, if not quite there yet: Atlantis Energy's SunSlate has a structural warranty of 25 years and 20 years for power. But the price tag is $12,000 per 100 square feet, which works out to $12 per watt. United Solar offers a 20-year warranty on power output for its solar roofs.

One other ambitious, exciting roofing possibility is the green roof, or eco-roof—which is, literally, green. Green roofs are vegetated—planted with anything from grass to flowers to trees—helping to cool the building, decrease run-off, and improve outdoor air quality. They are, of course, high maintenance, and not cheap in the short run, though they can reduce cooling costs by a quarter, double the roof's lifespan, provide sound insulation, and even serve as a garden or recreation area. Because of their weight and cost, most green roof efforts have focused on new buildings in urban areas. But modular systems are available, and even regular homeowners might be able to retrofit their roofs. See www.greenroofs.com/ for more information of all kinds; www.earthpledge.org/GreenRoof.html has information on a New York City initiative.

Resources

Department of Energy's webpage on How to Buy Energy-Efficient "Cool" Roof Products www.eere.energy.gov/femp/technologies/eep_roof_products.cfm#find

Energy Star's Reflective Roof Products page www.energystar.gov/index.cfm?c=roof_prods.pr_roof_products