When Via Verde opened in the South Bronx in 2012, the 222-unit affordable housing complex revived hopes that New York City would jump-start housing construction in communities that needed it the most. Nearly a decade later, the housing affordability crisis has only grown worse, just as a second, more existential crisis—climate change—has made its presence in the city increasingly felt. But a would-be sequel from Jonathan Rose Companies, the developer behind Via Verde, promises to pick up the mantle.
Sendero Verde in East Harlem is on target to become the world’s largest Passive House project. The completely affordable 709-unit complex, designed by Handel Architects, with further backing from L+M Development Partners and the nonprofit Acacia Network, is rising on a full-block site on 112th Street. Existing community gardens were preserved and embedded in the new configuration, flanked to the east by the elevated Metro-North tracks and just a few blocks from the northern stretches of Central Park. Sendero Verde offers a gradient of scale in three volumes: a high-rise corner tower (Sendero A), along with a mid- and a low-rise building (Sendero B). The tower is expected to open in 2024, while the latter set is due for completion in April 2022.
The massing and design of the project are, according to Handel Architects partner Blake Middleton, inspired by complex rhythms of music and harmonics: “A percussive pattern of colors in stucco and masonry echoes the underlying design concept and is used as a mechanism to break down the forms into a pattern of subtle colors that weaves throughout the facade.” The syncopated window openings, he added, have “underlaying structure rooted in the Fibonacci sequence.”
Incorporating Passive House design principles can be a costly decision and is sure to affect overall project budgets. For this reason, the design team relied on Passive House consultant Steven Winter Associates (SWA) and envelope consultant Vidaris, among others, to develop best-practice detailing procedures that also kept costs down.
First, SWA developed a Passive House Planning Package that established the performance criteria for the project. The consultants then evaluated the building design against these criteria, running THERM analyses on the facade assemblies and modeling individual thermal bridges. The design team reentered the picture and “studied each THERM analysis to determine if the thermal performance conformed to the project requirements or if there was any condensation potential,” explained Handel Architects associate Louis Koehl. “Each detail was refined until the individual conditions were satisfactory and the overall building Passive House criteria met.”
Sendero B employs the block-and-plank form of construction; in short, precast concrete slabs act as ceiling and floor and are placed atop load-bearing concrete masonry blocks. The relatively straightforward structural system allowed the application of a budget-friendly, liquid-applied continuous weather barrier. The facade is field-assembled, and there are two primary enclosure systems. The shorter southern building is clad with a 6-inch-deep field-applied exterior insulation finishing system, and a 3.5-inch mat of mineral wool insulation was applied to the back of the concrete masonry units, which are foil-faced to prevent interior water vapor from penetrating the facade system. The midsize building to the north is clad with a 4-inch-deep exterior insulation finishing system, and Handel was able to forgo interior insulation owing to the thermal mass afforded by the larger building size and the high performance of the windows.
Except for the storefront glazing found at the podium, all windows across Sendero B are triple-glazed insulated glass units (IGUs) placed within punched window systems. Here, too, performance was measured against the Passive House Planning Package. The project team assessed the U-values and Psi-values of the IGUs; for the former, they captured the values of each unit’s center and frame, while for the latter they clocked the Psi-values within the units and at their perimeter.
The energy-efficiency features of Passive House design are more than skin-deep, and that quality is certainly the case here. The buildings utilize a variable refrigerant flow for heating and cooling, and, thanks to the thermal performance of the facade, they do not require heating at the building perimeter. “Each apartment has a floor-mounted evaporator unit in a centrally located closet, and the air supply is ducted to each bedroom and living room,” Koehl said. “The evaporators are supplied refrigerant through vertical risers that extend to the rooftop condenser farms, and a major challenge was sourcing evaporator units small enough to support the minimal loads required by the airtight residential units.”
Similarly, the team had to identify energy-recovery ventilation units that could both handle the air distribution requirements and maintain a level of electrical efficiency in line with the project’s Passive House targets. It’s this attention to detail and performance that has put Sendero Verde on track for success.
Architect: Handel Architects
Location: New York City
Passive House consultant: Steven Winter Associates
Envelope consultant: Vidaris
MEP engineer: Cosentini Associates
Structural engineer: DeSimone Consulting Engineers
Mineral wool: Rockwool
Thermal breaks: Armatherm and Schöck
EIFS facade assembly: Dryvit