In an increasingly urbanizing world, certain downtown cores, such as Midtown Manhattan, have become highly desired spaces for firms to build office space. When a given building has a great foundation and solid structure, but doesn’t have the capacity to meet demand for its block, our architects have used densification as a unique, complex, and highly impactful approach for substantially increasing the square footage of a lot while reusing embodied carbon to minimize environmental impact.

Note

This article originally appeared in the spring 2023 issue of KPF Review. Watch the accompanying video here.

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

The warehouse turned office tower retains 85% of its original structure.

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.

Before (left) and after (right, credit: H.G. Esch).

After purchasing the site, our client, Cove Property Group, came to KPF for a design to take advantage of the extra floor area ratio (FAR) that was made available in the rezoning of the special Hudson Yards District. We worked with them to calculate the amount of area the site could accommodate within the zoning envelope. The typical FAR for the area was ten, and we received a bonus of three because the client donated to the Development Investment Fund. The GFA and the FAR both increased by nearly 75% by adding the overbuild to the project.

Interiors of the original structure.

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.

Credit: H.G. Esch.

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.

The ninth floor serves as the building’s transition from existing concrete structure below to new steel tower above, and repurposes the existing roof as a 13,000 square foot, lushly planted, wraparound terrace dedicated to the anchor tenant, Peloton. Outdoor space is provided on 75% of new overbuild floors in the form of a terrace or balcony, including the top floor that pairs a double-height interior with a dedicated landscaped area.

The ninth floor terrace. Credit: Mike Van Tassell.

One Madison Avenue

The transformation retains 67% of the original structure.

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.

Before (left) and after (right, credit: Motiv).

The goal of the project was to recapture the existing Zoning Floor Area (ZFA) on the building itself, which was achieved by removing the less efficient portions of the existing building on the upper levels and replacing them with a highly efficient tower on top of the existing building. Also driving the design strategy were a series of goals for the project, including achieving ten-foot ceilings in the tower, and in the existing building maximizing ceiling heights, integrating a new MEP system, and improving daylighting.

From the outset, the project has been driven by three main concepts. The first is a highly optimized tower configuration, which is achieved by positioning the core to the north side of the building; the second is weaving greenery through the project both in the interiors and in the form of outdoor space; and finally, creating specialty floors to serve as social spaces with unique architectural features and large terraces located at the intersection of old and new.

Credit: Mike Mehr.

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.

Large terraces provide over an acre of outdoor space for tenants, cementing the building’s connection to Madison Square Park. Credit: Motiv.

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.

Hudson Commons library lounge (left, credit: H.G. Esch) and ninth floor office interiors (right: credit: Mike Van Tassell).

When placed in the context of New York City’s Local Law 97 (LL97), which regulates a building’s greenhouse gas emissions, both Hudson Commons and One Madison Avenue are already significantly exceeding target emissions. LL97’s 2030 targets require a maximum of 4.53 kilograms of CO2 per square foot, and these two buildings are expected to achieve 3.25 kgCO2e / ft2 (Hudson Commons) and 3.42 kgCO2e / ft2 (One Madison Avenue), placing them about 33% below the maximum allowable emissions.

As the architecture real estate industries adapt to meet the challenges of the climate emergency, Hudson Commons and One Madison Avenue provide examples of how we can meet the demands of an evolving market, add value to existing buildings, preserve embodied energy, and improve operational performance.

One Madison. Credit: Motiv.