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Mill Valley Residence Sees Green (Roof)

Credits: ©2010 McGlashan Architects

The vegetated roofs on a Mill Valley, California, home hop, skip and jump their way down three levels following the slope of the hillside. The living roofs cover tiers of two homes that are woven together by a connecting stair so that the multigenerational family living there can share one floor but retain separate living quarters. Using salvaged and recycled materials, architect Scott McGlashan designed a super-insulated home that utilizes passive solar heating and cooling, an efficient hydronic radiant heating system, on-demand water heaters, and a water-saving on-demand hot water recirculation system, along with photovoltaics.


Mill Valley Veg Roof from Above

Vegetated roofs shelter three levels of living space while preserving habitat, with skylights providing daylighting and ventilation to rooms below, on this Mill Valley, California, home. ©2008 McGlashan Architecture

By P.J. Bremier, Marin Magazine,

March 2009 - Scott McGlashan had a hard time convincing his clients to add a living roof to the plans for their eco-friendly, energy-efficient home in Mill Valley until it solved one of the main design challenges: concealing a second unit.

His clients, a Tiburon couple, bought the canyon property several years ago with their son and daughter, intrigued by the idea of living alongside their children and grandchildren. “We jumped at the chance to get our family together,” McGlashan’s client says. “My wife and I (now) see a lot more of our grandkids.”

They had hoped to build three homes, McGlashan says, “but the (Mill Valley) planning commission was adamant there only be two. My clients didn’t want to share a house and they didn’t want to look out on another house, either. They really wanted the second unit to ‘disappear.’”

So, while the couple’s son and his family moved into the property’s existing home, they began planning their new home with their daughter and her two sons.

They hired McGlashan, a Berkeley architect, to come up with a solution that would marry a flexible floor plan with respect for privacy and a design as green and energy-efficient as possible.

The result was a three-story tiered home, each level topped by a living roof of colorful wildflowers. All the homes (units) have a separate entrance and utility hookup, yet all three families share a large solar array designed for net zero energy usage.

The grandparents occupy the top story of the newly constructed house, enjoying an open floor plan for kitchen, dining and living space along with a private sitting room, his-and-her offices and a master bedroom suite. A front deck traverses the length of the top floor’s large windows, which frame a view of Mill Valley looking toward San Francisco. A heavily tinted glass roof, its upturned edges inspired by the wingtips of local soaring raptors, masks a carport below the windows. A living roof cleverly conceals from view the lower, offset second unit. Consequently, all visual attention is gracefully directed outward.

The middle floor, which holds the couple’s guest/workout room, is flexible-use; it shares a Jack-and-Jill bathroom with the second unit, and that unit can legally “borrow” three bedrooms and a play space. In the future this level can be incorporated into the main house or become more securely partitioned and rented out as a studio or three- or four-bedroom apartment.

San Francisco designer Julie Massucco, who oversaw the finishes for both new units and furnished the upper house, balanced the desires of both clients. “The daughter wanted a lively, nontraditional and low-maintenance design for her space and her parents wanted a somewhat modern look, but not minimalist, more warm and comfortable,” she says.

Massucco pulled colors from the surrounding grasses and maintained harmony between the three floors by establishing a palette of greens and using coordinated hardware. To keep it environmentally green, she specified natural fabrics, low-VOC paints, water-based finishes and eco-friendly cabinets and whenever possible used local vendors. Upstairs, the owners’ furnishings were reupholstered for cleaner lines, and in the lower level unit, recycled glass countertops were installed.

For McGlashan, building to last was just as important as greenness of materials. “In my mind, that’s one of the more ecological things you can do,” he says. “The exterior is made of integral stucco so there’s no need to repaint; the fascias and trim are made of durable copper; and the roof should significantly extend the life of the protected membrane.”

He used Forest Stewardship Council–certified wood throughout, including White Tigerwood flooring from San Rafael’s EcoTimber and Douglas fir for windows, stair treads and custom doors. He also hand-carved a decorative column, a fireplace mantel and an entry bench out of beams salvaged from old projects. “Before I was an architect, I was a cabinetmaker, carpenter and boat builder,” he explains. “I still love getting my hands back into a project.”

Other green features include super-insulation, passive solar heating and cooling, fly-ash concrete, efficient hydronic radiant heating, on-demand water heaters, and a water-saving on-demand hot water recirculation system. “And considering the context, neither the upper level home nor the second unit is huge,” McGlashan says, acknowledging the high resource consumption typical of some large homes. “Approximately 5,500 square feet is shared between them.”

Special features in the upper unit will allow the couple to age and stay in place—a small elevator, wall blocking for future bathroom grab bars, accessible hardware, and a convenient foot pedal for the kitchen sinks. “They really love the Pedal Valves,” says McGlashan. “They wish they had one at every sink.”

Outside, the house was integrated with the topography to minimize grading and habitat disruption. The living roofs, which the owners originally thought might be too fussy but now admire, “make up for the habitat removed to make way for the (new) house, meaning little or no net loss of bird, plant, or insect habitat,” says McGlashan. “They also reduce storm water runoff and help keep the house cool in summer.”

The canyon is maintained by hand-pulling invasive Scotch broom, and three pet pygmy goats help keep the grasses trimmed and fire-safe. Garden paths are illuminated by LED or fluorescent lighting, shielded to minimize light pollution.

A simple set of stairs connects both homes and all families, allowing the grandparents, parents and cousins to be in easy contact. “Sometimes, the kids will stop in to say hi or maybe just wave as they go skipping down the stairs on their way somewhere else,” their grandfather says. He pauses and smiles. “It makes all the extra effort involved in building this house worth it.”

The Vegetated Roof
By Scott McGlashan -

The semi-intensive green roof was designed to balance weight, plant variety, and water efficiency. With no prior experience on green roofs, McGlashan Architecture did a crash course on the subject, gathering information from many sources to ensure a successful design. For the architect, the biggest challenge was getting a handle on the many overlapping fields of responsibility that converge on a green roof: roofing, landscape design and installation, material and soil suppliers, engineering, plumbing, sheet metal, etc.

For a first project in an emerging industry, the learning curve is steep. Along with a thorough study of the emerging literature (thanks, GRHC!), we consulted with, among others, Charlie Miller in Philadelphia and Brent Bucknum (formerly) at Rana Creek in Carmel, CA before we settled on a relatively simple section: 6-8" of lightweight soil over filter fabric over a Miradrain drainage mat over a root barrier over a Gaco Western cold liquid applied membrane, all supported on plywood decking and wood framing. The roof slopes are between 1/2" and 2" per foot. Irrigation is supplied with a Netafim Techline drip system. Completed in February, 2009, the roof continues to amaze and delight the owners.

Relevant books:
California Mediterranean
Green Roofs in Sustainable Landscape Design
EcoRegion-Based Design for Sustainability


McGlashan Architecture (Berkeley, California, USA)

Mill Valley Hillside Home Photo Gallery