"Passive House Public Schools: PS 456/KGIA," Metals in Construction, Vol. 22, 2025.
Wedged between two large residential towers and two historic buildings on a constrained triangular lot negotiating between low-rise Boerum Hill and rapidly growing downtown Brooklyn, a pair of public schools meeting strict Passive House standards used 1,315 tons of steel and employed smart design, engineering, and construction phasing to create enough space for 850 students. The decision to aim for the highest zero-energy environmental standards added unusual complexity to combining two visually distinct schools in one 146,000-square-foot structure meant to last at least 100 years.
When the project at 80 Flatbush Avenue was announced by Alloy Development in 2017, local residents denounced the scale of the 74- and 38-story mixed-use towers, the tallest originally set to top out at 986 feet. At the center of the block, Alloy planned to partner with the city’s Education Construction Fund, which works with private developers to build public schools accommodating the city’s ever-growing school-age population, issuing bonds to finance construction. But citing the development’s scale, bulk, and proximity to a residential district, the local community board’s land-use committee voted unanimously against the necessary rezoning. Without it, the towers could only reach a maximum of 400 feet.
Four months later, however, the City Planning Commission approved the rezoning anyway. Then, spurred by elected officials mediating between local opponents and the developers, Alloy agreed to reduce the height of the tallest structure by 146 feet, still more than twice as tall as the zoning otherwise permitted. The rezoning quickly cleared the rest of the public review process. Six years later, in the fall of 2024, two new public schools built to Passive House standards and a 44-story all-electric apartment tower with 440 rental units opened their doors. (The 860-foot-tall tower has yet to be started.)
Architect and Alloy co-founder Jared Della Valle led the design of the towers but brought in Architectural Research Office (ARO) to design the school building, having previously collaborated with the firm on a single-family house for Syracuse University’s Near Westside green-home initiative. “We’re good at making complex things not seem complex,” said Stephen Cassell, an ARO principal and the lead designer for the project.
The architectural strategy centered on two principles. First, the educational buildings would have their own distinct presence instead of being hidden within the towers. Second, they would meet a Passive House standard for energy conservation, anticipating Local Law 31 requiring more stringent energy-use reduction coming into effect in 2020. The law mandates that public buildings in New York City reduce energy use by 40 percent by 2030 and achieve a net-zero threshold by 2050, putting the schools 25 years ahead of regulations.
To give each component its own identity, ARO designed the high school so it would appear as a floating cube appropriate for a broad thoroughfare like Flatbush Avenue, while crafting the entrance to the elementary school to step down to a brownstone block on State Street. A cocoa-colored brick rain screen facade, syncopated with recessed and projected planes and high-performing punched windows, gives an expressiveness to the exterior facing Flatbush, while employing a neutral surface material that doesn’t stand out extravagantly in the neighborhood. A mesh trellis will eventually be overgrown with plants, providing a visual buffer for the terrace outside a third-floor cafeteria. “We tried to make something that felt like a civic building and told high school students it’s their building in the city,” Cassell said.
The cantilevered entry to the 350-student progressive elementary school, Elizabeth Jennings School for Bold Explorers, has a more residential feel to it, buffered by flowering planters, and its lobby has a lower ceiling. Meanwhile, the front doors of the high school—the 500-student Khalil Gibran International Academy, which provides Arabic language classes—has a more cosmopolitan, urbane sensibility. Its lobby opens onto a public plaza facing busy Flatbush Avenue, and its terrace and ground-level retail spaces add urban activity and continuity to the nearby commercial corridor on Flatbush. “We wanted the high school students to be integrated into the liveliness of the city,” said ARO project director Dominic Griffin.
Inside, most of the elementary school classrooms are on the fourth and fifth floors, with the high school on the sixth and seventh, and the third floor split between the two schools, separated by a pair of doors. Kitchen services are shared, but the cafeterias and gyms for each school are autonomous, and the terrace outside the cafeteria gives the high school students a private outdoor social area.
Structurally, the steel framing of the combined building is relatively standard: slab on metal deck, with steel and concrete slabs acting compositely to make a stronger steel section. Girders that are 21 to 24 inches wide and steel beams 14 inches wide span distances ranging from 132 to 190 feet, supported by steel columns set 24 to 28 inches apart. Most of the foundations are concrete spread footings bearing on four-ton-per-square-foot soil. Select areas with high concentrated loads or lateral uplift use steel micropiles drilled into the soil.
To achieve Passive House standards, the structure employs thick insulation, high-performing windows, a tight envelope, and thermal breaks between the columns and the foundation, using high-density polyurethane pads to prevent thermal bridging and interrupt the transfer of energy through the structure. “We’re starting to see such energy-conserving strategies even in projects that don’t aim for Passive House standards,” said Jason Tipold, structural engineer and principal of TYLin.
Engineering the complex geometry of the site demanded some delicate balancing of lateral structural loads and strategic cross-bracing set back from the façade to prevent daylight from being blocked. But the trickiest aspect of the project came from the constrained building site. Traffic on Flatbush Avenue could not be blocked during construction, and a subway tunnel runs directly adjacent to the site beneath Schermerhorn Street. That meant there was nowhere for the crane to sit except on top of the base of the building as it was being erected. Crane engineers had to reinforce the first floor of the building with extra thick beams to absorb the weight of the crane and materials being lifted, practically making the building a part of the construction machinery. Simultaneous construction of the 44-story tower also required the careful staging of work.
The other distinctively reinforced parts of the structure are a customized gymnatorium—a combined gym and auditorium—lit from clerestory windows facing State Street, a top-floor gymnasium, and a recycled-rubber-floored rooftop play terrace framed with AESS stainless steel tubes and tensioned wire mesh to prevent balls from flying off the roof. Because of the 60 to 63 foot spans of open space, the ceilings of the gyms are supported by long steel trusses with wide flange members, welded together by Orange County Ironworks in their Montgomery, New York shop and delivered to the site on trucks with extended trailers. Many of the mechanical building systems were hidden in the trusses to save ceiling space for the gymnatorium. The stainless steel and mesh cage of the play terrace also had to be specified as architecturally exposed structural steel to withstand exposure to the elements.
Ultimately, these highly specific, customized elements that negotiate the constraints of the site give the schools a strong civic presence. “It was a lot more work but it makes it a better building,” said Cassell, “and creates a school where students have a sense of belonging, engagement, and pride.”
With the development’s yet-to-be-started tower anticipated to be the second tallest in all of Brooklyn, there’s little doubt the complex will remain abhorrent to some residents of Boerum Hill, despite the appeasement of public schools, exceptional environmental standards, and the 45 low-income rentals so far included. But the project has already provided dozens of rentals far below the market rate and a pair of public schools whose design and construction met demanding environmental standards, pointing to a bright future for high-performing city institutions.
