Today, many office buildings in New York require significant upgrades to meet both demand and new regulations such as Local Law 97, which imposes strict carbon emission limits for buildings above 25,000 square feet. Two of our New York projects follow this strategy of targeted densification. By taking an existing, low-density structure and leveraging updated zoning regulations, we can expand the available square footage in the building. Hudson Commons and One Madison Avenue, through creative design solutions, both retain a significant percentage of their existing structures and introduce efficient overbuilds to achieve significant carbon reduction.

Hudson Commons integrates an existing eight-story building with a new 17-story tower to create a single, cohesive Class-A office building. Built in 1962, the existing 423,000-square-foot, cast-in-place structure was originally designed as a warehouse, and in 1983 was converted to office, becoming the longstanding home of Emblem Health. Hudson Commons occupies a prime site at the gateway to the Hudson Yards submarket, and the property benefitted from the city’s 2005 rezoning of the district, which kick-started the transformation of the area, including the Hudson Yards mega-development.

Part of the renovation of the existing building involved reinforcing the structure to accommodate what was essentially another building placed directly above in the form of the 17-story overbuild. Rather than introducing new columns throughout the podium’s floorplates to support the new tower, we selectively reinforced existing columns on each floor through a jacketing process, adding structural capacity in an efficient and cost-effective manner. In addition, we replaced existing ribbon windows, widening them by about 18 inches, adding more vision glass to bring more natural light into the podium floorplates.

A new, reinforced concrete core meets the lateral demand of the larger structure, and introduces additional elevator and mechanical capacity for the tower. The new core was threaded through the building from foundation to the top of the structure, articulating existing columns. Demolition for the new core was enabled by reinforcing the existing slab around the area to be demolished, some of the steel becoming part of the permanent structure. The result was a highly desirable side-core configuration positioned on the north side of the building. This allowed for efficient space planning and sweeping views to the south, east, and west which include every major landmark in NYC.

Following a similar strategy as Hudson Commons, One Madison Avenue transforms an existing, low story building into flexible Class-A office space. The project is located adjacent to the Five Madison clock tower, a New York City Landmark building that was once the tallest in the world, and across the street is Madison Square Park, which serves as a major source of design inspiration for the project. The existing building has a strong history of adaptive reuse. Starting in the 1900s, the building grew to expand with the Metropolitan Life Insurance Company, serving an integral purpose in the company’s multi-building campus on Madison Avenue.

One Madison Avenue is an as-of-right zoning building, meaning the scheme did not require any zoning variances. However, because both the Clock Tower and the existing podium were built before current zoning regulations, the buildings were not compliant. This required complex analysis, particularly at the transitional floors between podium and tower, to fit within the existing non-compliant area of the demolished floors while complying with the regulations as they relate to the Clock Tower.

The resulting floorplates are not only driven by the zoning requirements, but also our client’s demand for efficiency. In the tower, the core is located at the north side, which creates a 55% opaque wall at that façade, significantly reducing heat loss in the winter—a key component of the project’s sustainability features. This allows a 60-foot-deep, completely column-free floorplate at the south side with floor to ceiling glass and excellent views. In the podium, the core is also biased toward the north, creating a largely southern facing floorplate with new, taller windows that use high-efficiency glass and bring more natural light into these spaces.

Through both of these projects, we can see the environmental benefits of this approach to adaptive reuse. A lifecycle assessment of the embodied carbon saved by retaining the structure, which bears the majority of the embodied emissions, compared to what would have been its full demolition and then the construction of a new, similarly sized building with an equivalent structural system, shows that over 40% of emissions were saved in both cases. This is a significant savings, due to creative design and structural work. Put in context, the operational carbon produced after 20 years of operating the buildings is about the same as what was saved in terms of embodied carbon.

In terms of energy efficiency, both Hudson Commons and One Madison Avenue are very high-performing and energy efficient. The Energy Use Intensity (EUI) for each building is 46 kilobtu / ft2 (One Madison Avenue) and 42 kilobtu / ft2 (Hudson Commons). Both leverage a north-facing, side core configuration, high performance glazing, and a high window-to-wall ratio in the podium. The projects perform twice as well as the median office building in New York City, and far better than a recently completed, typical supertall office tower.