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Jim Callahan grew up on a ranch so he is most at home in the open air. But as an artist he also likes the convenience of his urban live-work pied a terre in downtown Sonoma, just off the plaza.

The sculptor figured out a way to have the best of both worlds after the roof starting collapsing over a funky addition to the historic building that houses his studio and second-story apartment (as well as the La Haye Arts Center and Cafe La Haye) on East Napa Street.

Instead of just replacing the roof, Callahan decided to completely rebuild the addition and create over it a so-called “green roof.”

The result is not just a rooftop garden of potted plants and outdoor furniture. It is a living roofscape, complete with plants and trees rooted directly into a layer of soil on top of the roof membrane.

Callahan can now enjoy the pleasures of a 900-square-foot outdoor living space with many of the same features that any homeowner might have in their backyard. There are pavers and a sunken patio of Peruvian travertine, softened by a lawn of drought-tolerant Buffalo grass that never needs mowing and is dog-friendly and comfortable to sit on. There also is a profusion of native plants like yarrow, California fuchsia and penstemon and a whole herb garden of rosemary, oregano, sage and terragon, as well as a variety of succulents. There are even trees — dwarf citrus with roots planted right into a soil medium laid over the membrane of the roof.

“I wanted it to be a living room in the same way that the great room in the house is a living room,” he said. “This is living space. We want to be out on it,” said Callahan while relaxing in the a lounge chair and hearing the pleasing hum of bees.

The architect of this landscape is Kevin Falkerson and his life and business partner, green roof designer Kerry Lee Cole. Their company Symbios, a Sebastopol architecture firm that specializes in green building, has been creating living roofs for about seven years. But their work remained largely under the public radar until several months ago when Amy’s Drive-Thru in Rohnert Park opened.

The first vegetarian fast-food drive-through eatery has been getting national attention. And one of it’s often-photographed features is a living roof, created by Symbios, that looks like a country garden or meadow unexpectedly thriving on a frontage road right off Highway 101.

REVIVAL TAKES ROOT

Falkerson and Cole have also created living roofs for the Ellis Creek Water Recycling Facility in Petaluma, Tte Salmon Creek School and Environmental Center in Freestone and Emerisa Gardens nursery in Santa Rosa.

While sod roofs were historically common in rural Scandinavia, the modern revival and iteration first took root in the 1960s in German. It slowly made its way through Europe and over to the United States.

But it didn’t really start catching on in the Bay Area until 2008, when the striking new Renzo Piano-designed California Academy of Sciences opened in San Francisco with an edgy green roof filled with 1,700 plants embedded within 50,000 porous, biodegradable vegetation trays made from tree sap and coconut husks.

The idea was to create an urban oasis for birds and insects. Over the last seven years it has become a signature feature of the museum, providing insulation and thus reducing energy needs for heating and cooling, capturing excess storm water and serving as a filter to transform carbon dioxide into oxygen in the middle of the city.

Sonoma magazine remembers 10 beloved Wine Country restaurants, landmarks and wineries destroyed by the fires here

MANY BENEFITS

Living roofs have a lot of practical and environmental benefits, said Falkerson, a licensed architect with a master’s degree in architecture from Rennselaer Polytechnic Institute as well as a bachelor’s degree in ecology from Hampshire College. One of the most significant is improved building performance.

“A living roof will keep a building much cooler in summer. It’s a wonderful passive collecting system. No longer is the sun hitting the roof membrane and conducting that heat down,” he said.

Because of the weight of the soil and plants, a living roof in most cases is practical only for new construction. A structure must be engineered from the beginning to handle it, making it an integral part of the building itself. It’s not just a load of soil dumped on a roof but an intricate and sophisticated system.

On top of the regular roof membrane a waterproof membrane is placed that serves like a wetsuit. It is on top of that that Falkerson and Cole add addition layers including a synthetic, non-rotting material that retains moisture and into which plants can root.

Over that they lay a lightweight engineered soil. They recommend a minimum of four inches with an optimum of six inches depth for a greater diversity of plants.

The thinner layer can support ground covers and succulents like sedum. But for a more diverse planting like Amy’s Drive-Thru, you’ll need six inches.

Falkerson and Cole don’t use potable water to irrigate their roofs. They use reclaimed water, graywater or harvested rainwater. For Callahan they installed a rainwater catchment system that captures rain from the roof, stores it and pumps it back up to the roofscape.

CEILING CAVING IN

He hit upon the idea of a living roof after the ceiling began caving in on the addition where he had his studio. He decided to build a whole new space for a pop-up gallery.

“The walls had to be great big studs walls and a new foundation capable of supporting everything as well as extra shearing,” he said.

Emerisa Gardens recently built a new sales and office building, a rustic, shed-like structure with a living roof by Symbiosis that serves as a living billboard for the nursery’s plants.

For their roof landscape they chose shallowly rooted, herbaceous ground covers, including Echeveria elegans ‘Blue,’ Thymus serphylum ‘Mauve’ and Yucca gloriosa ‘Bright Star.’ A dominant theme are Sedums — ‘Dragon’s Blood’ for its red foliage, ‘John Creech’ with its green foliage and ‘Tricolor’ which is variegated.

“Many dwarf ornamental grasses are also nice as they add movement and texture to the palette,” said Weaver, who also recommends not growing plants that require too much deadheading and maintenance “as the roof can start to look messy and unkempt very quickly.”

Because of the complexities and the potential damage that could be wrought if not done properly, a living roof is not for the do-it-yourselfer, although Cole said one could probably get away with creating a living roof on an shed using pond liner.

Cost varies greatly but averages about $30 a square foot for a residential project, Cole said.

“The cost after that is for maintenance and putting in new plants,” she added. “You do lose some to frost and age. And they will require some maintenance. But you will never have to put in another roof and underneath, you will be saving with your heating and cooling.”

LIVING WALL

Those with an existing home that can’t support a living roof could opt for a living wall. Falkerson and Cole also make vertical gardens made of similar materials and plants that are less expensive and outfitted with drip irrigation for easy maintenance.

Callahan loves his new yard, which feeds the bees that he keeps in a bee box on another roof.

The landscape overlooks an alley next to the old Sebastiani Theatre. He and his girlfriend, Kelley Anderson, frequently project their own outdoor movies onto the side of the historic theater.

“The thing that I find really fascinating about this whole idea is that it is, in fact, a roof,” said Callahan, a sculptor and Sonoma resident for more than 35 years. “And it’s an urban space that has green stuff growing on it. Having lived in a second-story apartment with no access to the roof or outside for years, this suddenly increases my living space. It makes it possible to have a dog, which I love, and it makes the quality of life better all the way around. Right now I’m sitting outside watching the birds and bees flying around. It’s pretty good urban living.”

You can reach Staff Writer Meg McConahey at meg.mcconahey@pressdemocrat.com or 521-5204.