A few blocks from the High Line, the restored elevated railway bed that now sports pedestrian walkways amid a landscape of greenery, New York City’s Chelsea Green is a 14-story luxury condominium from Alfa Development.
Designed by Stephen B. Jacobs Group (with DJM Construction and structural engineers WSP Cantor), every aspect of the 6875-m2 (74,000-sf) concrete structure is intended to consider its impact on the environment. Green attributes are found everywhere from the cabinets and HVAC to the rainwater irrigation system and vegetated roof. To ensure ultimate efficiency, light-emitting diodes (LEDs) have been mounted throughout the building and solar shades installed above the windows.
Additionally, thermal break connections are being used in the balconies on the 11th through 14th floors to further enhance the building’s energy performance. Recently approved by the NYC Department of Buildings, these 52 concrete-to-concrete thermal breakmodules are being installed on 10 of the 2.3 x 4.9-m (7 ½ x 16-ft) balconies at Chelsea Green to deal with thermal bridging otherwise occurring where the envelope is penetrated.
Each balcony at Chelsea Green is cantilevered out 2.3 m on 203-mm (8-in.) thick tapered concrete slabs.
“Traditional balcony attachments deal primarily with only the structural cantilever and, as a result, transmit exterior temperatures to the interior floor slabs, adding to the energy use of the unit,” said Alfa’s senior project manager, Frank Mattiello. “This thermal bridge effect can be felt when walking barefoot in one’s apartment—even when the heating or cooling systems are in operation.”
The structural thermal breaks provide load-bearing thermal insulation for these slabs and transfer bending moment stress and shear forces. Their integrated hanging and tensile reinforcement mitigates use of other costly elements like stirrups or hooped mat.
“This is a major breakthrough for combating thermal bridging in New York City residential buildings,” said Stephen B. Jacobs Group’s Omalawa Abdullah-Musa. “The process for getting this product incorporated into the project was challenging, since it was relatively unknown to most structural engineers here. Chelsea Green has set the tone for future projects, and we are looking forward to spreading the word about this innovative technology.”
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