Melissa and Rian Jorgensen's green roof -- literally a succulent garden growing out of a horticultural mixture spread directly onto the surface -- provides a pleasant view from their master bedroom.

But the view is really a bonus: The Jorgensens' roof garden insulates the whole house and ultimately cuts down on energy use.

Their roof garden is a far cry from the traditional roof originally planned when renovating their Menlo Park home. But their architect, Jonathan Feldman of Feldman Architecture, San Francisco, pointed out the benefits and the Jorgensens soon agreed.

"We were coming from a home with no insulation, and the idea of a green roof eliminating the need for air conditioning was a huge attraction," Melissa said.

The Jorgensens' roof faces a grove of redwoods that provides partial shade and thus negates the benefits of solar panels. However, the roof still gets plenty hot, particularly in summer.

According to San Francisco landscape architect Stephen Suzman, principal of Suzman & Cole Design Associates, whose firm designed the green roof on this year's San Francisco Decorator Showcase, a green roof can lower the rooftop temperature from 130 degrees down to 75 degrees on a typical summer day.

"Plants transform heat and soil moisture to humidity, which produces natural evaporative cooling," Suzman said.

"If everyone had a green roof it would help eliminate global warming," said Suzman, adding that the cooling effect is particularly desirable in densely populated cities where the heat island effect can be mitigated.

The initial cost estimate for the Jorgensen's 500-square-foot garden was $8,800. As with most ecologically smart designs, the cost benefits in energy savings accrue over time.

Further, the structure of a green roof is protected from ultraviolet radiation and extremes in temperature variations. While a traditional roof lasts anywhere from 15 to 50 years, a roof like the Jorgensens' can last anywhere from 50 to 100 years, according to Nigel Dunnett and Noel Kingsbury, authors of "Planting Green Roofs and Living Walls."

Feldman points out that the green roof necessitates the use of larger supporting beams --in this case, steel beams. The extra structural costs were not factored into the roof-garden budget.

What the costs covered, in addition to design and installation fees, were the first layer of plastic coating, the roof barrier, the drainage mat (facilitates drainage), the capillary mat that holds water and encourages plants to take root, a subterranean drip system, a filter fabric so that the soil won't clog, a lightweight planting medium and the seedlings.

Suzman's firm is currently testing LiveRoof, a green roof that can be installed in panels of established plants. The theory is that these plants can better withstand the roof environment than can seedlings.

The interior staircase wasn't in place when they installed the garden, so workers accessed the roof with ladders, carrying buckets. Now the master bedroom opens directly onto a small deck and garden beyond.

"We needed to use the lightest mix (15 pounds per square foot) and the thinnest planting depth (1 1/2 inches) to minimize load bearing," said Lauren Schneider of Wonderland Garden and Landscape in Oakland, who designed the Jorgensen garden. "The only plants that could survive there would be succulents, which store water in their leaves."

An "extensive" green roof features a growing medium of 2 to 6 inches (16 to 35 pounds per square foot). An "intensive" environment, with more depth, typically found in a more urban setting, can even include trees.

Suzman is currently working on a Palo Alto home with a green roof composed of tufted hair grass and red fescue planted in waves, designed by his firm's landscape architect. Although extensive, it necessitates a deeper growing medium than the Jorgensens'.

"Lauren had some really cool ideas for the design," Melissa said. Schneider chose several varieties of sedums and simper vivums, both of which spread, as well as non-invasive miniature ice plants and aloes. "I wanted to create an imitation of a larger landscape," Schneider said.

"It takes about a year for everything to fill in," said Schneider, adding that three or four maintenance visits are required during that time to weed. "After that, you need someone to weed about once or twice a year."

Feldman stresses that maintenance has to be done by someone experienced enough not to tear the underlying protective layers.

"A green roof can also muffle sound as much as 40 decibels," Suzman said. In order to appreciate this, he explains that 30 decibels is the difference between a lawn mower and normal conversation.

Suzman also points out that these roofs reduce the amount of water that runs off into the streets by absorbing 50 to 95 percent of rainfall, thus reducing the pollution carried into the Bay. They also contribute to cleaner air since many of the smog-forming chemicals are filtered by the plants.

Although the United States lags far behind other countries, such as Germany, in offering government incentives and tax breaks specifically for green roofs, Feldman suggests checking if local areas offer any benefit program for green projects. "In some areas, if you have a high enough green rating your project will get expedited," he said.

Plus, Schneider said, in a lot of cities, the square footage of a roof garden, as compared to decking or patios, doesn't count towards the total allowable for hardscape. "So, you could plant a part of the roof that you wouldn't use anyway and use more square footage elsewhere," she said.

Despite their environmental benefits, it is too soon to know whether green roofs represent a trend in the U.S. --particularly in the suburban landscape. "The Jorgensens are really pioneers," Schneider said.