Supertall buildings may no longer be a novelty, but that doesn’t mean they’ve become easier to build. Manhattan tower 520 Fifth Avenue, a 1,002-ft-tall, 450,000-sq-ft mixed-used structure on track for completion later this year is a case in point. Rising from a constrained quarter-acre corner site at the busy intersection of Fifth Avenue and 43rd Street in midtown, the project has a crowded setting that required general contractor Suffolk Construction to combine its supertall building experience with what the company says are “advanced data analytics and cutting-edge technology” to efficiently plan and execute each phase, an effort that began well before construction got underway in January 2022.

Tom Giordano, Suffolk general manager for the New York region, says that with so little room to work with, every aspect from logistics to protecting workers and managing street traffic has been addressed well in advance and synced with scheduled construction tasks to keep the project safe and on schedule. “We’ve been compiling data from the start, giving us a clear data lake to work with,” Giordano says. “We’re constantly receiving updates on progress and upcoming areas that we’ll be focused on. That helps alert us to potential problems that we can avoid.”

With an aspect ratio of 1:15, the thin profile of 520 Fifth Avenue belies a structural brawniness that begins with the site’s underlying Manhattan schist.
Rendering by Binyan Studios, courtesy Suffolk

Strong Foundation

With an aspect ratio of 1:15, the thin profile of 520 Fifth Avenue belies a structural brawniness that begins with the site’s underlying Manhattan schist, “some of the hardest foundation material in the world,” says James von Klemperer, president and design principal for architect Kohn Pedersen Fox. “It’s a strongly resistant subsurface condition well suited for a building of this type.”

With the site long vacant since demolition of a nine-story office building in 2013, Suffolk got right to work excavating the foundation to about 48 ft below street level, removing rock using a combination of line drilling and breaking. According to the contractor, the foundation mat thickness varies from 10 to 19 ft, with walls averaging 36 in. thick. The building’s elevator pits, which continue to 60 ft below grade, are founded on a 36-in.-thick reinforced concrete pit slab.

Once at street level, site logistical constraints required a multiphase strategy that began with a Liebherr 542 crane founded at grade and used for concrete construction through Level 21. This tower crane was replaced by another Liebherr 542 founded on a cantilevered platform on Level 8, which supported the balance of the project. Suffolk says routing pedestrian traffic at the busy intersection inside the building instead of on the sidewalk under the crane operation, improved safety and reduced constraints on adjacent bus lanes.

The superstructure consists of 72 floors of reinforced concrete slabs supported by concrete columns. Along with belt floors located on Levels 32 and 52, Suffolk says Grade 97 rebar combined with concrete and steel link beams further reinforce the building core while also alleviating rebar congestion and reducing shear wall thickness.

The tower superstructure consists of 72 floors of reinforced concrete slabs supported by concrete columns. A multicrane scheme optimized the schedule for each core and shell trade.
Photo by Katherine Marks, courtesy Suffolk

A two- and three-day pour cycle allowed placement of the concrete superstructure to finish three weeks ahead of schedule. To speed material delivery as the building gained height, Suffolk installed a main four-car hoist complex that served the first 64 levels, with a single car hoist providing access to Levels 64-72. Another secondary hoist was used for below-grade levels.

Because a series of asymmetric setbacks narrows the building as it rises, Giordano says coordination was particularly critical to top the 76-floor concrete superstructure in October 2024 with five levels of galvanized structural steel framing and grating platforms that enclose and support a 500-ton tuned mass damper, mechanical systems and building maintenance unit. A combination of prefabrication and a select overtime system allowed structural steel work to be completed in late December, seven weeks ahead of schedule, the contractor says. In total, Suffolk says the project has more than 6,000 tons of rebar, 29,000 cu yd of concrete and 1,000 tons of structural steel.

Von Klemperer says that while the building’s complex structural strategy required “a tight set of engineering maneuvers,” the resulting layout accommodates developer Rabina’s planned variety of uses.

To reduce column sizes for the building’s lower 30 stories—which include ground-floor retail, lobbies, meeting areas and 25 floors of office space with 12-ft ceilings—Suffolk built a 31-story, 24-in. by 24-in.-thick composite structural steel column on the project’s prominent corner of 43rd Street and Fifth Avenue, with the plate column tied back to the concrete shear wall core at three floors. “The columns in the building find their place in the plan without obstructing views where we wanted the views to be,” von Klemperer says, adding that even with the smaller upper-level floor plates, “we can get good depths for residential parts of the building.”

The building’s exterior includes distinctive arches made of glazed terra-cotta panels on the podium levels, with painted aluminum panels for the upper levels. The exterior also includes 5,500 unitized curtain wall panels.
Photo by Katherine Marks, courtesy Suffolk

Onward and Upward

Giordano says that while 520 Fifth Avenue encountered similar pandemic trade and material impacts as other projects, once construction activity picked up, work has progressed with few problems.

Activity now is focused on completing installation of the building’s exterior, which includes distinctive arches made of glazed terra-cotta panels on the podium levels, with painted aluminum panels for the upper levels. The exterior also includes 5,500 unitized curtain wall panels. Plans call for office floors to be completed in September, Giordano says, while residential sections are to be turned over in phases during the ensuing nine months.

“The advance planning and coordination have paid off, and we’ve had a good collegial environment across the project team,” he says. Although Rabina has not disclosed a total project cost, Giordano says the team plans to deliver the finished building on budget.

The mixed-used tower, which is on track for completion later this year, includes a residential penthouse with a spacious primary bathroom.
Photo by Alden Studios, courtesy Suffolk

Ian Klein, senior vice president and head of development at Rabina, has high praise for the “meticulous and creative logistical planning” that enabled Suffolk to erect a supertall tower alongside a heavily trafficked street such as Fifth Avenue.

“The Suffolk team thought through these complexities from the outset, using a multicrane scheme to optimize the schedule for each and every core and shell trade,” the executive says. “We were all excited to see the last beam set atop the building in December, ahead of schedule.”

According to von Klemperer, the project proves that a supertall mixed-use building can be built not only on a tight city site, but also amid existing dense surroundings. “Finding a spot of superdensity and making that density even more accessible to people living in the building is a net gain for everybody, both inside and outside the building,” von Klemperer says.