A Cheaper Way to Build a Roof Deck

Roof decks are a coveted amenity in New York, especially with the weather finally warming up. For co-op and condo boards on a tight budget or in buildings that can’t support a major load on the roof, there’s an affordable alternative called 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. 

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, Eric Cowley, president of Cowley Engineering, says that only a quarter of the 50 buildings he has inspected in the past year 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 or with a wood-and-plastic composite such as Trex. “But if you use non-combustible materials such as concrete pavers or aluminum planking – aluminum planking is often used to achieve a similar aesthetic of a wood deck and is lighter than pavers – you will not be limited to the 20 percent coverage requirement and 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. 

Many of Cowley’s 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 a steel overbuild. “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.”