Concrete Office

Heavy Building, Light Look at 505 Fifth

by Amy S. Choi

The architects of 505 Fifth Ave. in Midtown Manhattan hope to create the "lightest" possible building by using the heaviest material.

"The top priority was always to have a transparent building with the most possible light," said Christopher Stoddard, project manager on the job and senior associate principal at New York-based Kohn Pedersen Fox Associates, PC.

As project owner, the Kipp-Stawski Management Group decided to go with one of the newest concrete technologies on the market with that goal of achieving visual lightness. The 30-story office building will be one of the few towers in New York featuring high-strength concrete in 15-ft. cantilevers, 30-ft. columns, and 11-in. thick concrete slabs. The cantilevers will allow for a column-free perimeter, slim spandrel beams, and 11-ft. floor-to-ceiling windows - all of which help the interior capture as much light as possible. They will also maximize views of nearby landmarks such as Bryant Park, the New York City Public Library, and Rockefeller Center.

"Usually the spandrel is nearly 3 ft. wide, so you'll see alternating spandrel and glass covering an entire building," said Marc DePaul, project manager at Pavarini McGovern LLC in New York, the project's construction manager. "In this design, you see nearly all glass. The entire curtain wall will be seen."

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The convergence of glass and concrete provides the most interesting visual tensions in the property, Stoddard said. The atypically large vision panels and interior laminated glass will both ensure safety and maximize penetration of sunlight into the floor plates.

But these intersections also provide some of the bigger construction challenges. The construction team is paying especially close attention to the curtain wall inserts to make certain they are in the proper location, because the structural concrete offers little tolerance for even the smallest errors.

"Concrete is a wonderful thing, but it has to be engineered and constructed with a lot more controls and advanced technology [than structural steel]," Stoddard said.

Steel often has an edge in taller office high-rises, in part because it typically allows for taller floor heights. But concrete also offers its rewards. For an owner that wants more design freedom within an office structure, concrete allows the option to displace the building core, putting the utilities in the corner of the floor plate rather than through a centralized shaft. The 505 Fifth design has those displaced utilities, allowing the architects to install a hardened, concrete-enclosed core with emergency egress stairs for occupants - a growing security priority for tenants.

Working with concrete can also speed up the development cycle, thus saving money. Though steel is generally less expensive to buy, it requires more time for engineering and fabrication. Concrete usually takes a longer time to install on a site than steel, but once poured, the structure is largely set. With steel, once a structure goes up, the project team must wait for fireproofing, losing time on the schedule.

Supporters of concrete design also argue it's safer than steel, making it an ideal product for terror-mindful New Yorkers.

"You don't have to rely on spray-on fireproofing with concrete," DePaul said. "The owner went with concrete because it's safer, has better stability, and this particular building was designed so that if you lost a column on the ground-floor level, the building would be able to self-sustain the structure. We're seeing more concerns on this topic coming up."

As a result, concrete is slowly gaining status in the city. Though 505 Fifth, which broke ground in February and is slated for completion next September, is one of the few buildings currently utilizing concrete, it will not be the only new property highlighting the material in the next few years.

Pavarini McGovern, for example, is currently bidding on 140 W. 42nd St., which will be a post-tension concrete building using technology almost never used in Manhattan. The growing popularity of concrete is due in part to The Concrete Alliance Inc., a New York City-based advocacy group of union trades, contractors, and associations. New York-based Kipp-Stawski, which has long been a champion of concrete development and used it to build 360 Madison Ave., has joined forces with the Concrete Alliance to promote concrete as a building material.

At a May symposium organized by the New York City Concrete Promotional Council, Tony Leichter of Kipp-Stawski said concrete not only is a safer material, but also has a "one-stop shopping" aspect. "We like very much the idea that these are local materials that can very easily be shipped into New York," he said.