The residents of The Oaks Zero Energy Neighborhood at Rose Villa Senior Living are reaping the benefits of an opportunity that is unfortunately rare—the chance to live out their environmental values while cultivating a deep sense of community. The Oaks, a neighborhood of 12 homes for older adults in Portland, Oregon, opened its doors last February. The buildings are designed to meet their own energy needs through a combination of Passive House-based design and on-site renewable energy generation.
All 12 Craftsman-style homes in The Oaks sold before build-out—a testament to the market demand for eco-friendly senior living options and to Rose Villa’s commitment to creating ample opportunities for residents who want their homes to match their social and environmental values. “Many people think of senior living communities as places where they may have to give up their way of life. At Rose Villa, we offer many ways people can continue to live their values and do the things they love,” says Vassar Byrd, Rose Villa CEO.
Portland-based Green Hammer Design Build led the design and construction of The Oaks. Established in 2002, Green Hammer is a leader in zero-energy and Passive House design principles. (Green Hammer was one of 16 firms that in 2019 met the goals of the American Institute of Architects’ 2030 Commitment, a voluntary effort to achieve carbon neutrality in the built environment by 2030.) The firm’s previous experience designing and building zero-energy multifamily projects in the Portland region, including Ankeny Row and Tillamook Row, helped it to complete the Oaks Neighborhood early and below budget.
The Oaks’ success is already increasing the availability of this housing type. Green Hammer and Rose Villa are working on a second zero-energy neighborhood, Trillium Townhomes, which will include six new 1,200-ft2 zero-energy townhomes. Completion is expected in the summer of 2022.
Green Hammer applied Passive House design principles to drastically reduce heating and cooling loads at The Oaks. The homes are expected to achieve a 70% reduction in total building energy use relative to existing comparable buildings. With tight building envelopes and efficient mechanical ventilation systems, the homes provide residents with unparalleled comfort and health benefits. “Indoor air quality and thermal comfort are important for people of all ages—especially those with asthma, allergies, or other health concerns,” says Erica Dunn, Green Hammer director of design.
In designing The Oaks, Green Hammer incorporated Passive House design elements that are common to all of its projects, starting with superinsulating the envelope and making it airtight. To minimize thermal bridging, the shell is wrapped with 1½ inches of mineral wool insulation and the wall cavities include 7¼ inches of blown-in cellulose insulation. Cellulose was used in these 2 x 8 Forest Service Council-certified walls to help reduce overall embodied energy and increase moisture storage capacity in the building. Triple-pane, tilt-turn windows keep the homes warm in the winter and cool in the summer, making them more resilient in times of extreme heat or cold and during power outages.
The airtightness was achieved using a diffusion-open, breathable membrane formulated for roofs with a parallel product on the walls, sealed with a proprietary tape at the seams and penetrations. A liquid-applied membrane was used for continuity of the air barrier between the diffusion-open façade membrane and the stem wall and for slab penetrations and connections of the slab to the stem wall. An expanding-foam tape was used to insulate and air seal the windows to the framing. The slab was insulated continuously below with 4 inches of EPS type 2 and type 9 as needed for structural. One and one-half inches of type 2 EPS was used to insulate between the slab and the stem wall.
The roof assembly consists of raised-heel scissor trusses with 20 inches of blown-in fiberglass, chosen for its light weight and high R‑value. The trusses do not overhang the walls, but instead sit flush, allowing the roof membrane to be attached directly to the top of the trusses and taped over the membrane adhered to the walls below. To create the Craftsman-style overhangs and a vent cavity, 2 x 4 lumber was placed on its side over the top of the membrane and plywood was then nailed to the flat 2 x 4s. Green Hammer employs this assembly on many of its projects to make an airtight and code-approved ventilated roof assembly.
Heat-recovery ventilation systems provide continuous fresh, filtered, outside air to each bedroom and living space within every home while continuously extracting air from the kitchens and bathrooms. Each home is heated and cooled with a single, centrally located wall-mounted mini-split heat pump.
State-of-the-art CO2-based heat pump water heaters cut water energy use by half compared to the next highest performing options currently on the market. Energy Star-rated appliances and low-flow water fixtures keep energy and water use down.
A 74-kW on-site solar-panel array, spread out among south-facing roofs and the south-facing carport, generates clean, renewable energy. As these buildings are all-electric, this renewable-energy production is expected to supply all of The Oaks’ energy needs on an annual basis.
In addition to energy-saving measures, Green Hammer incorporated universal design elements such as no-step entrances and roll-in showers that allow residents to live independently as their health and physical condition changes. Meanwhile, pedestrian paths and a shared courtyard encourage people to go outside and engage with their neighbors as well as nature—which includes enjoying the historic oak tree central to the site, around which the neighborhood was designed.
“By combining the Passive House design standard with universal design principles, we’re creating durable, healthy, comfortable spaces that can adapt to people’s changing needs,” Dunn says. “Zero-energy homes are becoming more common because homeowners are realizing the huge return on investment—not just in energy savings but in their health and well-being.”
The lessons learned from this zero-energy community—the first of its kind in the Portland senior housing marketplace—will help Rose Villa and other developers meet a growing demand among baby boomers for housing options that allow them to minimize their ecological footprint while maintaining a high quality of life.