It is Thursday evening, time to water the lawn. Jacek Perkowski slips on some flip-flops and walks through a glass door in his open-air living room. He grabs a hose and gets to work. But Perkowski isn’t watering the grass in his yard; he’s watering his roof. There, above the rafters of his three-bedroom house, a seven-inch-deep carpet of sod grows in green velvet chunks. “The idea of having parties on the roof, this kind of thing, was very important for me,” says Perkowski, a Polish rock musician and former member of T. Love. “It’s another way of enjoying and living in and around the house.”

Perkowski isn’t alone. While in the wilds of Książnice, Poland, where Perkowskilives, a yard on the roof may be seen as eccentric, throughout much of Europe sod roofs are becoming common. About 10 percent of German roofs have been “greened,” many with sod, and Great Britain hopes to catch up to this number soon. Since January of 2004, over 3 million square feet of greater London’s roofs have been turned into green space. Green Roofs for Healthy Cities (GRHC), an industry association of green roof builders in North America, estimates that its U.S. members installed more than 2.6 million square feet of green roofs in 2008, a 35 percent increase over the year before.

But beyond being a good place to sip a drink or host a party, what’s the benefit of having to water and mow your roof? “There are hundreds of benefits, actually, both financial and environmental,” says Steven Peck, president of GRHC. “Sod roofs [and other green roofs] retain heat in the winter and cool a house in the summer, saving about 25 percent per year in climate-energy costs.” Peck says that many new houses built with green or grass roofs require smaller, less expensive heating systems. And they are quiet, insulating a building’s interior from street noise. Then there are the environmental benefits. A single 16-square-foot roof of uncut grass produces the amount of oxygen that one person breathes in an entire year and removes up to 4.4 pounds of airborne pollution annually. Depending on the depth of growing media and the frequency and duration of rainfall, green and grass roofs also retain anywhere from 10 to 95 percent of the precipitation that falls on them, greatly inhibiting runoff and decreasing floods. And the list goes on.

Scandinavians have known the wonders of sod roofs for thousands of years. “Between 5 and 10 percent of the houses here still are sod,” says Tórálvur Weihe, head of the department of historical and protected buildings at the National Museum of Faroe Islands. Here, in this cluster of 18 mystical islands in the North Sea lodged between Iceland and Ireland, is one of the highest concentrations of sod roofs in the world. The Faroese continue to employ an age-old method of building sod roofs: Base layers of birch bark (or sheets of knobbed plastic) are placed on roof panels, then covered with sod cut from surrounding yards. It’s as simple as that. “When covered in sod, the roofs can last about 50 years without any reconstruction—–about five times longer than a standard asphalt roof,” Weihe says.

But before you start digging up your front yard, consider that not every house can support a sod roof. “This is not a do-it-yourself technology—–there are serious structural implications and a lot of things that need to be considered before grass roofing,” says Peck.

To ensure standards are met, in May 2009 GRHC debuted a Green Roof Professional (GRP) certification program for green roof developers. Similar to LEED certification (the U.S. rating system for environmental design), the GRP program establishes guidelines and systems for green and grass roofs. The first four-day training course GRHC offered for GRP certification sold out.

Back in Poland, Robert Konieczny, owner of Katowice-based KWK Promes and architect of Perkowski’s sod-roofed house, says his attraction to sod roofs was less about making the roof like the front yard than about making it an extension of the ground. “We wanted to keep the fluidity of the grassy clearing surrounded by the forest where the house is located,” says Konieczny. “Instead of just cutting and moving grass onto the roof of the house, we bent the ground up around the house.” Doors and walkways that might ordinarily lead to a yard lead instead to the sod roof area, making the rooftop indistinguishable from the surrounding grass flats and creating what Konieczny calls an outside atrium. “The goal was to create a new type of space,” says Konieczny. His inventive approach earned the project a nomination for the European Union’s 2008 Mies van der Rohe Award.

Konieczny is planning similar sod roofs for upcoming projects. “It’s wonderful. Not only does it create a very positive microclimate inside the house, but for me, sod versus other green roofs is much less hassle to maintain. And I love the appearance of having grass on a roof.” And, lest we forget, it’s a great place to party.