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After a fire, this multifamily building was renovated into an energy-efficient home, thanks to Boston-based architect ZeroEnergy Design.
From the outside, the tan triple-decker on Columbia Street in Cambridge looks a lot like the other multifamily homes in the neighborhood. Tall and narrow with three apartments inside, it reflects a common architectural style found throughout Boston's densely packed neighborhoods. But this particular building tells a unique story, demonstrating how affordable and sustainable living can go hand in hand.
A few years ago, a fire severely damaged the roof and interior of the building, displacing the residents of all three units — each occupied by low-income families through the Cambridge Community Housing Development (CCHD). The 4,680 square-foot building required urgent reconstruction, and CCHD sought a solution that would not only restore and modernize the structure, but also enhance its energy efficiency, sustainability, and safety. They turned to ZeroEnergy Design, a Boston-based architecture and mechanical design firm known for its expertise in energy-efficient buildings.
Stephanie Horowitz, co-founder of ZeroEnergy Design, spoke with Bluedot about the extensive interior renovation, detailing how the team focused on modernizing the building while selecting sustainable materials to eliminate its reliance on fossil fuels and bring it up to code. Triple deckers are a common typography in Boston, Cambridge, and Somerville, and notoriously hard to renovate, Horowitz noted. This project shows how it can be done sustainably and affordably. Most importantly, the original residents were able to move back home. “I think that’s really the success of the project,” Horowitz said.
All Electric and Air Ventilation
For heating and cooling, the ZeroEnergy Design team went with air-source heat pumps.
“There’s an outdoor unit that hangs off the back of the building that you might be able to see off the rear-porches,” Horowitz said. “And there’s an indoor unit that’s located in a drop ceiling that’s accessed from a closet.”
The air-source heat pumps are ducted and provide both heating and cooling to each unit. The heating and cooling system is paired with an energy recovery ventilator (ERV), which is also a ducted unit that provides continuous fresh air to the living spaces. The ERV also extracts stale air from the bathroom and kitchen.
“The distribution ducts for the heating and cooling system are not co-mingled with the ventilation system,” Horowitz noted. “So, for example, if the tenant is not calling for heating or cooling, they’re still getting continuous fresh air regardless of whether the heating or cooling system is on.”
Having the dedicated systems for heating and cooling and fresh air distribution “is a best practice for our firm,” Horowitz said. “Something that’s perhaps not common in the industry.”
Energy Star Appliances and Efficient Fixtures
“Where applicable, we used Energy Star appliances,” Horowitz said. (See box below.) The team chose an electric range over an induction, which was preferred by the client. Each decision was led or proposed by the design team, Horowitz said, with feedback from the client, CCHD.
The kitchen faucet and other plumbing fixtures have a WaterSense certification, meaning they use less water than conventional fixtures. “It’s a standard that identifies fixtures that conserve more water than some of their peers,” Horowitz said.
Insulation and Air Tightness
The team went with two types of insulation: cellulose and mineral wool.
Horowitz noted that the damage from the fire was primarily to part of the roof and interior, and that the building’s siding “wasn’t at the end of its useful life, so we kept the existing siding on the building.” The team picked a dense-packed cellulose insulation made from recycled newsprint “which was blown into the stud cavity and we also furred out the interior walls,” Horowitz said. This allowed the team to “install an interior air barrier for air tightness and keep all the systems, like plumbing and the electrical wire, inbounds of that continuous air barrier,” Horowitz said. Cellulose insulation ”has a really great environmental profile as it relates to its embodied carbon, so that’s a common choice for us,” Horowitz added.
There was this really unfortunate event, luckily no one was injured, but it became an opportunity to really extend the lifespan of the building, to address the energy efficiency, to electrify the building, and decoupling it from fossil fuels.
– Stephanie Horowitz, co-founder of ZeroEnergy Design
The mineral wool insulation has a slightly higher carbon makeup, “but it has a lot of other things going for it relating to acoustics, ease of installation, and fireproofing capabilities,” Horowitz said.
For the roof, the ZeroEnergy Design team used cellulose insulation that was paired with polyisocyanurate insulation “used for continuous insulation as well as to achieve the pitch that was needed for the roof drainage,” Horowitz said. The team chose not to install solar panels because “we would have had to do a fair bit more reinforcing to the roof system,” Horowitz said.
Windows and Light Fixtures
The windows at the Columbia Street home are triple glazed and high performance. They have a “tilt turn operation,” Horowitz said, which is more common, “but they have a really great air-sealing gasketing system that makes them airtight.” The window frames “are really well-designed to mitigate thermal bridging and to take full advantage of the three panes of glass,” she added.
“We really seek out windows like this one that are designed for three panes of glass and have a nice healthy airspace between each of the panes,” Horowitz said. “This improves the overall performance and makes optimal use of the cost and carbon associated with that third pane of glass.”
For light fixtures, light emitting diodes (LEDs) are the most efficient and longest lasting.
Open Floor Plan
The ZeroEnergy Design team kept the floor plan on all three units relatively similar to their original layouts, but opted for a more open concept. “The general bedroom-bathroom layouts more or less worked, so the intervention on the floor plan was really to create a more open kitchen-dining-living area,” Horowitz said. Part of that decision is a lifestyle choice, but Horowitz acknowledged that open floor plans save space. “As part of the renovation we’re able to reclaim space essentially by making the living space more efficient,” she said.
Now, the Columbia Street triple decker maximizes energy efficiency and there’s no combustion onsite. The home is Enterprise Green Communities Certified, and is also certified under the Department of Energy’s Zero Energy Ready Homes program.
“It’s affordable housing in a dense, urban neighborhood,” Horowitz said, reflecting back on the project. “There was this really unfortunate event, luckily no one was injured, but it became an opportunity to really extend the lifespan of the building, to address the energy efficiency, to electrify the building, and decoupling it from fossil fuels. And the original residents at the end of the process were able to move back into the community, into the neighborhood, where they have established relationships and ties. That was wonderful to see.”
About ZeroEnergy Design:
ZeroEnergy Design’s mission is to “create beautiful, healthy buildings to empower families, uplift communities, and improve our living world.” The multidisciplinary team of architects, designers, and engineers have taken on a number of projects throughout Massachusetts, including custom home projects in Westport, Belmont, and Brookline; multifamily buildings in Taunton, Cambridge, and Jamaica Plain; and net zero projects in Somerville; Acton; and Providence, Rhode Island, among many others. They also take on projects for offices and businesses. See the full portfolio.
Resource Checklist:
Energy Star products “are the same or better than standard products, only they use less energy,” according to energystar.gov. To earn the Energy Star, appliances must meet strict energy efficiency criteria set by the U.S. Environmental Protection Agency or the U.S. Department of Energy. For example, qualified refrigerators are at least 15 percent more efficient than the minimum federal efficiency standard, and qualified lightbulbs use two-thirds less energy than a standard incandescent bulb. Read more here.
Energy recovery ventilators (ERV) improve indoor air quality by exchanging indoor air with fresh outdoor air. Unlike a simple exhaust fan, an ERV manages both temperature and humidity. Read more here.
Air-source heat pumps can deliver up to two to four times more heat energy to a home than the electrical energy it consumes. Read more here.
Zero Energy Ready Homes Program is a high-performance home that is so energy efficient that a renewable energy system could offset most or all the home’s annual energy use. These homes meet rigorous efficiency and performance criteria and are verified by a qualified third-party as part of a certification process. Certified homes are eligible to receive a tax credit. Read more here.
To learn more about ZeroEnergy Design and its number of sustainable design and architecture projects across New England, visit zeroenergy.com.
