Up on the roof: turn that heat island into a living system. (House & Home).

Your roof: it keeps the elements out, the warmth in. But, as green movers within the building trade are showing, reconfiguring this little-appreciated home component can pay very big dividends for the planet. Indeed, technology in recent years can help us transform the flat, bland shingles of our modern roofline into watt savers, energy producers and even wildlife habitats.

Coloring it White

Black absorbs sunshine and gets hot; white reflects it and is cooler. Elementary school science predicts that whiter roofs will naturally be cooler than darker ones. Even so, the numbers still surprise. One recent Florida study found that a white roof reflects a whopping 80 percent of the sun's heat, compared to a mere eight percent for one colored dark gray. That "cool" roof translates into indoor temperatures that are 20 percent lower, saving the average homeowner $130 a year in cooling costs.

A number of companies offer products that lighten up dark roofs. Some are white polymer membranes that are laid down over an existing roof; others are viscous coatings that are "painted" on. There are also pre-fabricated, light-colored tiles, shingles or metal sheets to replace old roof materials. Like most roofing jobs, this one's best handled by the pros.

When buying coatings, membranes or files, look for products that carry the Energy Star label, means they've met the Environmental Protection Agency's (EPA) criteria for energy efficiency and reliability. For a list of qualifying manufacturers, see www.yosemite.epa.gov/estar/consumers.nsf /content/roofbox.htm. You'll find manufacturers broken down by roofing type through the Heat Island Project, a government group that promotes strategies for lowering temperatures in urban areas (www.eetd.lbl.gov/HeatIsland/CoolRoofs).

Growing it Green

In the last half decade another compelling eco-roofing strategy has literally been taking root on an increasing number of housetops around the globe: the green roof. Inspired by the sod-roofed homes of Iceland and the American prairie of old, the modern living roof is a garden green that grows right over an existing roof, covering the monotonous shingle-scape with lush, variegated foliage.

To the environment's great benefit, the plants on these elevated greens trap dust and absorb airborne pollutants, like carbon dioxide. They also absorb and reflect less of the sun's incoming radiation than standard asphalt shingles do, keeping both indoor and outdoor temps cooler. Those lower temperatures can, in turn, trim demand for air conditioning, sometimes by as much as 30 percent.

A landscaped rooftop also captures some 50 percent of the rainfall that washes off a shingled roof. As a consequence, less water runs straight to storm sewers over-taxed by heavy rains. Plant roofs offer a measure of protection as well, doubling the roof's lifespan, and they provide a welcoming environment for birds, butterflies and other wildlife.

To grow your own green you'll need to layer your roof with a water-tight membrane, a drainage system, a soil mix three inches deep or so, and shallow-rooted plants hearty enough to endure full sun and exposure to the elements. A handful of companies produce complete green roofing systems and offer guidance on design and installation, including GreenTech, Roofscapes and The Garland Company.

Enthusiasts have raised their own green roofs, but many more hire landscape architects with expertise in the field. Landscapers typically contract installation of the gardens substructure to roofing specialists. If you tackle the project yourself, make sure to first consult with a structural engineer, who can calculate your roof's load capacity, and City Hall, which may have regulations pertaining to rooftop gardens (requiring, perhaps, fire escapes). You'll find tips in the pamphlet Rooftop Gardens ($7, from San Francisco Beautiful); Theodore Osmundson's book Roof Gardens (Norton, $75); and Greenroof.com.

Collecting the Sun

Mounting solar panels to the rafters is a time-honored straw of greening up a roofline. Now, thanks to advances in photovoltaic technology, it's possible to shingle your roof with solar tiles. Roofing shingles manufactured by Atlantis Energy and United Solar Systems--among others--are actual solar cells, ultra-thin collectors mounted onto sturdy fiber cement backing.

To encourage consumers to green their roofs, an increasing number of local utilities and state departments of the environment have begun offering rebates or tax deductions toward the purchase of watt-saving technologies. CONTACT: Atlantis Energy, [phone], www. stli.com/atlantis; Garland Company, [phone], www.garlandco. com/green-roofs.html; GreenTech, [phone], www.greentechitm.com; Roofscapes, [phone], www.roofmead ow.com; United Solar Systems, [phone], www.uni-solar.com.

MARK HARRIS is a Pennsylvania-based freelance writer.