Going Green Above Ground: Using Vegetation on a Roof
Vegetated roofs are a logical—but uncommon—solution for desert homes.
By John Roark
Rooftop gardens have long been a staple in cities where arable land is scarce and concentrated vertical living offers few alternatives. But how would an above-structure green space fare here in our often-unforgiving climate? Landscape architect and Phoenix Home & Garden Masters of the Southwest award winner Steve Martino pondered the viability of a vegetated roof populated with plants indigenous to the Southwest. “A friend of mine told me 30 years ago about a house he saw in Mexico that had a prickly pear roof, and I had been thinking about it ever since,” he says. “We were working on a property that had a shed with a tar paper roof. It seemed like the perfect place to give it a try.”
Relying on his own knowledge and instincts, Martino reinforced the roof and, using two-by-fours, created a matrix that he filled with 2 inches of decomposed granite. He then overlapped almost 1,000 prickly pear pads, embedding the ends into the limestone to take root. With virtually no maintenance the rooftop is still going strong years later. “We just scratch our heads and say, ‘It worked!’” he laughs.
Having grown up in Norway, architect Tor Barstad, also a Phoenix Home & Garden Masters of the Southwest award winner, remembers seeing “torvtak” (grass roof) houses and was curious why this wasn’t a common practice in the U.S. “I later learned that not only can vegetated roof systems last hundreds of years, but they also have other favorable qualities in addition to the undeniable aesthetic appeal, including tremendous insulation value, great sound absorption and healthy environmental benefits,” he says.
Passionate about the concept, Barstad has designed numerous homes with rooftop garden systems, but has yet to see them built. “Because vegetated roofs are not common in Arizona, this has always been an uphill climb,” he says.
Both Barstad and Martino stress that a rooftop garden should not be commenced without professional assistance, as factors such as roof pitch and strength, waterproofing and drainage must be considered.
“I firmly believe that vegetated roof systems are by far the best roof option in Phoenix and will be a game-changer for comfort and long-term affordability,” Barstad says. “To me, this practice connects a structure to the environment in the most sensitive and appropriate way possible. I would love to see people discover how it can be done in a beautiful way that harmonizes with the desert.”