CASE STUDIES

380 STUART STREET, BOSTON

A 28-story, 625,000-square-foot commercial building soon to appear on the Boston skyline (see Figure 5), just off the boards with construction about to begin, may defy customary assumptions about the energy performance of curtain walls. At 380 Stuart in the Back Bay, careful product selection, design creativity, and a willingness to invest in triple glazing are setting new standards without abandoning the visibility that full curtain walls provide.

Rendering courtesy of CBT Architects

Figure 5. 380 Stuart Street on the Boston skyline.

Boston’s building code is among the most rigorous in the U.S. for emissions performance. “We have net-zero carbon zoning, which was recently implemented,” notes Henry Celli, AIA, LEED AP, CPHC, principal and senior architect at the Boston-based firm Childs Bertman Tseckares (CBT); a 2023 update of Massachusetts’s 2009 stretch code is “much more rigorous,” he says, “allow[ing] us to basically balance between energy systems and our wall assemblies. They’ve targeted the wall assemblies very specifically, and that is playing a big factor in our developments these days.” With prescriptive, performance, and certification paths, so that “being a Passive House project will get you through the state energy codes,” this regulatory environment is driving impressive rates of decarbonization.

CBT’s all-electric, all-curtain-wall office building at 380 Stuart Street, which Celli describes as “net zero as defined by the city,” is a salient example, with a modeled 48 percent lower energy use than a similar noncompliant office building. “There’s a lot of discussion out in the sustainable world about how sustainable an all-curtain-wall building can be,” he says. 380 Stuart’s unitized curtain-wall system, fabricated offsite to tight standards with “a few well-engineered joints coming together on site,” is “incredibly efficient and very robust on the air infiltration side,” using argon-filled triple glazing with black stainless steel spacers by the German provider Interpane “basically everywhere,” two-surface low-E coating, fritting, and a chassis by the Connecticut firm Fabbrica; all these features combine to achieve a U value lower than originally specified.

“We tried to think about the number of panels that would be required to be installed on each floor,” Celli says, recognizing that the aluminum component in a curtain wall with standard five-foot modules would be considerable (and its embodied carbon likewise) in a building with some 180 panels enclosing the facade. “We developed some scripts, using some of our software, in a way to get us the most efficient layout of a curtain wall on our floor plan.” This step saved 30 or 40 panels per floor, improving the U value and sparing cost. The designers investigated integrated PVs as an additional energy source but determined that shadows from neighbors to the east and west limited performance; PVs at 380 Stuart are confined to the roof.

Celli acknowledges that triple glazing adds weight and embodied carbon while noting that the choice was preferable to pricey, risky options like vacuum insulation. “The current stretch code almost forces us to use triple glazing,” he says. Only a very low window-to-wall ratio, he finds, “probably less than 30 percent,” would provide the desired metrics with double glazing. “A multifamily project could potentially get there, but a large commercial office building could not survive something like that. You just wouldn’t be able to lease those floors if you only had 30 percent glazing in the facade. Nobody wants to be 300 feet up in the air and only see small portals through your wall.” The occupants of 380 Stuart, will have their views, distinctive floorplans, and unique profile without compromising their green standards.

BRONX MUSEUM SOUTH WING

The public museum in New York City’s northern borough underwent an expansion and renovation by Arquitectonica in 2006, doubling in size by adding a striking new accordion-like folded facade of steel and glass, rising asymmetrically from the Grand Concourse sidewalk. The original museum building, however, a 1961-vintage former synagogue, remained largely untouched, recalls Marvel’s senior architect Carolina Cohen Freue, and posed multiple problems involving heating, lighting, and a sense of disconnection from the new space. “We were tasked with bringing the campus together and creating a new entrance,” Cohen says, “to open its doors, open its art, make it more visible, let it breathe, make it clear where you go, and make it clear that it’s one campus with different buildings rather than a disjointed Frankenstein approach.” The expanded south wing moves the main entrance to the Grand Concourse-165th Street corner (see Figures 6 and 7) and revises the interior circulation to connect all galleries in a continuous loop, welcoming the neighborhood in.

With funding and guidance from the city’s Department of Citywide Administrative Services (DCAS) and sustainability consultation by Atelier Ten, Cohen and colleagues replaced the thinly insulated metal-paneled south facade with high-performance triple-pane IGUs, attaining R values that go beyond code. Roof-mounted PVs allow unusually high energy harvesting for an urban site; “we really don’t have a lot of shadow from the building across the street,” Cohen notes, since the museum faces south-southwest and the Grand Concourse is wide (approximately 180 feet streetfront-to-streetfront including sidewalks). Additional green features include a radiant floor in the lobby, all-electric systems (somewhat fortuitous, she acknowledges, after a gas-fired boiler died), efficient lighting controlled with daylight sensors and the building management system, and a highly insulated rainscreen roof with an extended marquee reaching beyond the property line to increase shading. The glazing includes an acid-etched two-by-four dot pattern for bird safety, compliant with Local Law 15 (which requires bird-friendly materials on post-2021 construction) and chosen over fritting or ultraviolet patterns.

Photo courtesy of Marvel

Figure 6. Rendering of Bronx Museum’s Grand Concourse elevation, with Marvel’s renovated south wing at right, Arquitectonica’s northern facade at left.

CaCohen notes that the building will pursue LEED certification, offsite renewable-energy credits, and LCA credits for material use, though it is not planned as a strictly net-zero project. Removing gypsum walls and “ugly metal panels” dating from before the addition of the corner atrium, the architects are leaving original brick and concrete exposed, “embracing that materiality” from the 1960s building while updating sections of the wood flooring. The museum is streamlining its public identity–“it’s not called the Bronx Museum of the Arts anymore,” Cohen notes; “it’s called the Bronx Museum”–and reimagining the brightly daylit new lobby as “the Bronx’s living room.” Marvel’s entire intervention occurs at sidewalk level, and the architects have borne in mind “this idea of people hanging out on their stoop; that’s very prominent in the Bronx.... We have an image of a bodega, of someone behind the counter, and we always keep that vibe as we develop the design.” Instead of a monumental staircase, the lobby has bleacher seating and a café; unlike most of New York’s cultural institutions, this museum is free of charge. “It’s not just a destination for [people] to go see the art,” Cohen says. “We want people to roam and stay there and linger.”

Photo courtesy of Marvel

Figure 7. Bronx Museum, evening view.

ONE JAVA STREET

This 789,000-square-foot mixed-use complex, linking five buildings on a full city block on Brooklyn’s Greenpoint waterfront (see Figure 8), is running ahead of New York City’s ambitious decarbonization timetable, thanks to an array of technologies and design ideas. Scheduled to open by late 2025 or 2026, the all-electric One Java will be among the city’s greenest major residential projects, aiming for net zero and contributing to developer Lendlease’s effort to reach absolute zero carbon by 2040, Mission Zero. Its other certifications include LEED Gold, Fitwel, ENERGY STAR, and the Waterfront Alliance’s Waterfront Edge Design Guidelines for outdoor public space and protection of native plant and bird species.

Image courtesy of Marvel

Figure 8. North and south towers at Brooklyn’s One Java Street complex, with neighboring building The Greenpoint in the background and lower-rise One Java building at right.

The high-performance envelope combines precast concrete panels with continuous interior insulation wrapping the two largest towers (37 stories in the piling-supported south tower, 21 in the north), providing tight thermal control, long-term durability, safety of installation, and energy savings that over the long run will counterbalance the carbon intensity associated with precast production, which the architects acknowledge is relatively high. Marvel’s Jeremy Iannucci notes that the facade “draws on Art Deco ornamentation” as seen around New York, expressing the building’s character through material diversity, along with easing construction and providing reliable, predictable performance.

The lower portion of the towers uses hand-laid brick, which is substantially less carbon-intensive than the panels. The complex has the largest geothermal system of any New York State residential project, including a vertical closed-loop liquid circulation system with a heat pump to apply the differentials from the Earth’s underground temperature (about 55° F, warmer than surface air in winter, cooler in summer) for heating and cooling, avoiding reliance on fossil fuels. The system won financial support from a New York State Energy Research and Development Authority (NYSERDA) pilot program and has 53 percent lower annual heating and cooling emissions than conventional natural gas boilers and cooling towers, saving the equivalent of 1,050 metric tons of CO2.

Marvel’s Dennis Vermeulen describes One Java as “net-zero-ready,” a condition required by one of the financing partners for the project: “When clean and sustainable, renewable electric is available, then they will buy that. But it certainly doesn’t mean that all the materials and the embodied carbon in the project are offset.” Reducing operational loads, he says, is essential, “and any fossil fuels you might be purchasing, you’re going to buy offsets to get to net zero.” Such calculations are secondary to the project’s efforts to create a viable community in this fast-developing neighborhood: it will contain 30 percent affordable housing, and it includes smaller six-story brick buildings on the side streets (see Figure 9), counterbalancing the towers with contextually scaled components. With landscaping by James Corner Field Operations, ample public space near a ferry pier, and no program located below the floodplain (allowing for storm surges at its riverside site), One Java reflects Marvel’s rethinking of the relationship between urbanity and nature.

Image courtesy of Marvel

Figure 9. Smaller-scale components of the One Java complex.

MALIBU HIGH SCHOOL

Malibu, Calif., is known nationally for beaches, celebrities, and a pleasant Mediterranean climate, yet its residents face certain hardships. “The power grid in Malibu is unreliable,” says Nathan Bishop, AIA, LEED AP, principal at Koning Eizenberg Architects (KEA) in Santa Monica, and “it’s a high fire zone. The infrastructure, gas, electric: everything’s pretty unreliable. It’s kind of a small town, really. So the school district really wanted a building that can function on its own in a state of emergency, whether that’s a wildfire or the power’s out.... We needed some very fire-resistant exterior materials, with the added layer of it being sustainable and being local, because it’s really expensive to ship things to Malibu: it’s, like, one road.” KEA’s design for the 500-student Malibu High School, working with energy consultants Verdical Group, is thus a net-zero building both by intention and by necessity.

Bishop is a proponent of low-tech architectural solutions, studying vernacular traditions and heeding climatic imperatives. In southern California, a building’s relationship to the sun is often a primary driver of design. “We’re looking for more passive ways to offset the demands on the glazing systems,” he says: “movable shades or awnings or some combination. The roof often has a pretty strong role to play.” The new school’s roof line is a solar-panel armature, which provides shading along with collecting energy. “Really bright light from outside in a school isn’t a great environment to create, and it’s not always something you can control just with the curtain wall alone unless you’re using shades.”

Aiming to harmonize with the rusticity of the hillside setting and avoid the kinds of curtain-wall mullions and detailing that strike him as “pretty slick and sometimes generic,” Bishop and colleagues included operable windows in the curtain walls in every classroom, fostering a sense of permeability between the building and its surroundings. The school’s teaching model involves project-based learning; “they have conventional classrooms, they have science labs and humanities classrooms,” he notes, “but they all hug around these little nested communities, around project-based and studio spaces.... Making a classroom outside in Malibu means making it so it’s not super windy and it’s not too sunny to actually conduct class, so that armature also covers key outdoor spaces for shading” (see Figure 10).

Image courtesy of Koning Eizenberg Architects

Figure 10. Malibu High School’s shaded outdoor space.

The range of heating and cooling days in Malibu is narrow, Bishop says. Facade elements and mechanical systems are driven by energy models linking performance to time and orientation. Light shelves work on the south facade but are avoided on the west, where the sun angle is low and vertical fins are preferable (see Figure 11). Testing insulated panels within the curtain-wall system, the team found that they did not perform as well as “integrating it into cladding.... The performance of the aluminum frame is not as great as framing up a wall, so we switched from having a lot more curtain-wall system, with some solids integrated into it, to dialing that back, having more built wall that performs better energy-wise.”

Image courtesy of Koning Eizenberg Architects

Figure 11. Shade study for Malibu High School by Verdical Group.

California’s Title 24 energy standards are ambitious; “just by meeting base energy code in California, you’re already into the LEED Gold area,” Bishop comments. “With this project, we went all the way down to the Bunsen burners, trying to get to an electrical Bunsen burner” and designing for conversion to an all-electric kitchen. Awareness of the fire hazard led to “a dedicated air system that can be filtered for the whole building in case of a fire, and that [led to] having a radiant system” for cooling and heating. “A lot of our projects look at low-tech approaches, so that it’s not just an engineering problem of the curtain wall... just reduced to ‘Gosh, now I need really high-performing glass that’s going to be dark or highly reflective and ruin my transparency.’” Recalling “a time where LEED gave you more points for a very efficient air-conditioning system than they did if you didn’t have an air-conditioning system at all,” Bishop relies on a back-to-basics approach: “beyond the engineering calculation... just some common-sense thinking-through about what it takes to build the building, the materials you’re building it with, and who’s going to use it.”