A Roof Deck Project Is Not a Place to Save Pennies

Paul Gans, project manager at New Bedford Management, has learned from experience that roof deck projects can turn into minefields. At several properties, he was hired when roof deck projects were partially complete – and headed for disaster. The problem was that the decks were being laid directly on the roof membranes. 

“We’ve had a couple of situations where we had to put the brakes on client jobs,” Gans says. “They didn’t do the load calculations, and they were in huge trouble. When [our] structural engineer looked closer and did some probes, the framing wasn’t large enough, so they had wasted $50,000 on an architect, designer fees, and planters and paving stones already ordered. The entire project had to be cancelled at a loss of over $70,000.”

The answer, says Gans, is building a structure to carry the weight of the deck. “Without a structural roof deck, where you’re using a steel span to [support] the load from parapet wall to parapet wall – a process known as dunnage – there are a lot of negatives involved,” he says. “When you put a roof deck directly on a roof line, it can cause warranty issues with a new roof product. It doesn’t allow water to flow freely or drain properly, and it transfers noise, so the penthouse owners will always be upset about noise and vibration on their ceiling. You’re limited to what you physically put on the deck because there’s only a certain amount of pounds per square foot you’re supposed to use for certain roof warranties, and just for safety.”

If clients are considering a roof deck, Gans always advises them to consider a structural roof deck, which roughly doubles the cost but addresses potential problems. Steel dunnage can also accommodate large planters and more elaborate landscaping. Despite these advantages, Gans says, it’s often hard to convince a board to spend an extra $100,000 to bring up steel beams to span the existing roof. “The ones that do it, are very thankful they did because it’s clear sailing for many years to come,” says Gans.

Newer buildings with structural concrete can usually handle heavy roof loads. But many prewar buildings in New York are wood-framed, and this is where co-op and condo boards need to hire an engineer to open the roof in several locations and insert probes to examine the original construction. By measuring beam sizes, engineers can calculate the load a roof can safely carry. 

“There’s only one right way to do it, and it’s a structural roof deck,” concludes Gans. “Every other way is a recipe for disaster. It’s expensive, and it’s a tough sell, but the smart boards do it because if they don’t, there will be issues down the road. The ones who want to save pennies don’t do this, and it always ends up biting them sooner or later.”