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Getting Decked Out

When it comes to amenities, a rooftop deck takes the prize. Even if the view isn’t spectacular, being able to relax al fresco in a secluded setting is a top-tier luxury. So it’s no wonder older buildings have been installing wooden decks or pavers up on their roofs, provided the building is strong enough to carry the extra weight. For buildings without that kind of muscle, however, decks have been an impossible dream, since strengthening the underlying structure usually involves tearing up the existing roof and putting in new beams and joists – a huge undertaking that would cost a small fortune. But there is a more affordable alternative: a steel overbuild. Simply put, it’s an elevated platform supported by the parapet walls, or by short columns set directly on top of existing support columns, thereby taking the load off the roof. If your co-op or condo board has been dreaming of getting all decked out, here’s what you need to know.

Birth of the Overbuild

“Think of an overbuild as a table that supports the deck flooring itself, but hovers on top of your roof without actually touching it,” says Eric Cowley, president of Cowley Engineering, who supervised the recent installation of a steel overbuild at the Hudson Gables co-op at 125 Cabrini Boulevard in Washington Heights. The board had something relatively modest in mind – a freestanding, elevated deck, roughly 20 by 40 feet, on the west side of the building, facing the Hudson River and the George Washington Bridge. Problem was, the roof joists at the six-story, 39-unit property, which was built in 1927, would be strained past the breaking point.

“In many older steel- and wood-frame buildings like this one, there are flat ceilings on the top-floor apartments, but the roof is sloped to allow for rainwater drainage,” Cowley explains. That creates an empty space called a cockloft – similar to an attic – and the angled rafters above it are rarely strong enough to carry the load of a recreational roofing system as well people, chairs, tables, and plants.

In narrow buildings, an overbuild – basically, a steel frame made of joists supported by girders – can be constructed in several ways. It can rest on the parapets, or sections of the parapet walls can be dug out to create pockets, where the girders are mortared in. The larger roof at Hudson Gables made those configurations impossible. But overbuilds can also be supported by “stub” columns, created by extending internal steel columns upward through the roof membrane, which then serve as the table legs. The structural steel columns at Hudson Gables were located in the right place and were also strong enough to make this scenario possible. Completed in 2016, the handsome 790-square-foot elevated deck, which has a composite-wood plank floor and a 42-inch railing, offers breathtaking views. The price tag was $69,000. Not surprisingly, it’s so popular with residents that the board had to install a walkway made of rubber pavers, Cowley says, “to protect the roof from spilled cocktails and high heels.”

Can I Get an Overbuild?

For boards contemplating steel overbuilds, the first step is to determine whether your building passes muster. “Perimeter walls have to be checked to see if they can support additional weight,” says Michael Larkin, a partner and senior structural engineer at RAND Engineering & Architecture. “Usually they’re okay. But if you can’t do a wall-to-wall deck, there have to be strong internal columns, which isn’t always the case in older, smaller buildings.” For his part, Cowley, who has inspected some 50 buildings in the last year, says that only a quarter of those have gotten the go-ahead.

Work can’t begin, however, until the city’s Department of Buildings approves construction plans and issues a permit, which it will do only if a state-licensed professional engineer or registered architect designs the deck. “City code allows combustible materials as long as they don’t cover more than 20 percent of a roof’s total area,” says Jeremy Côté, project manager at Howard L. Zimmerman Architects. That limits the size of platforms made with wood such as ipe, a popular Brazilian hardwood, or with a wood-and-plastic composite such as Trex, which was used at Hudson Gables. “But if you use concrete pavers or aluminum planking – there is metal flooring that looks and feels like wood – you can build something as big as you like,” Côté says.

And don’t forget the fire department. “They need to be able to put a ladder against your building and land on the roof, not the deck,” says Cowley. “There are thousands of buildings out there that don’t offer that access. As decks become more popular, the fire department is catching up with the trend and doing regular inspections, and you could get fined.”

A deck – whether it’s laid directly on the roof or hovers above it – is likely to outlive the roof membrane itself. So the roof needs to be in good shape before a deck is installed. With steel overbuilds, there needs to be enough space between the roof and the deck floor – at least two feet – for workers to repair or replace the roof membrane. “If you’re doing an overbuild, we encourage people to replace the roof first or do a new covering, so you minimize the amount of time you have to spend under there,” Cowley says. Or you may want to have your architect design a hatch somewhere in the flooring, with removable grating on the overbuild frame itself, so workers can get in there to clean out soil and debris, advises Côté. “Otherwise, the roof could deteriorate.”

The Last Word

Cowley says that many of his clients decided to explore steel overbuilds at the same time they were replacing their aging roofs. That was the case at 302 East 88th Street, a seven-story, 61-unit co-op in Yorkville that was built in 1957.  “Our roof was 33 years old and needed to be fully replaced,” says board president Melissa Siegel, who had been shown photos of the deck at Hudson Gables by the the co-op’s managing agent. “We were still bidding it out, and since the deck issue had come up at annual meetings for years, we decided to price out an overbuild as well.”

Incremental assessments had already been imposed to pay for the roof repairs, and some shareholders balked at having to shell out more for a deck. It was put to a vote, and the co-op’s older residents, many on fixed incomes, nixed the project in a 30-19 vote. “If it were up to me, we’d revisit this, the sooner the better,” Siegel says. “Older buildings like ours don’t offer many amenities, and a deck would help us keep pace with other properties. Maybe next time.”



When installing a recreational roofing system, an important consideration for boards is how it will affect the roof warranty. The typical No Dollar Limit warranty, which covers the full cost of replacing a roof for the entire term of the warranty (usually 20 years), will be voided if alterations or additions are made to the roof that don’t conform to the manufacturer’s specifications. If, say, you put in a wooden deck or pavers and your roof begins to leak, the warranty won’t hold even if the problem has nothing to do with the new installation. Technically, a steel overbuild deck won’t affect a warranty since it doesn’t touch the roof, explains Michael Larkin, a partner at RAND Engineering & Architecture, “but it’s still a good idea to contact the manufacturer to make sure they don’t have a problem with an elevated system.”

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