Why Are Roof Decks Complicated?

Christa Waring, Principal
CTA Architects

The Lay of the Land

Back in the day, when you wanted to put a roof deck on your building, you just hired a contractor and he came and put a surface on top of your roof so that people could walk on it. It might be wood, it might be concrete pavers. Then you put some plants up there and a sign on the door that said what the house rules were, and you had a roof deck.

But things are not that simple today. I think everybody understands that enforcement is a very high priority at the Department of Buildings. There’s a number of things that you have to do to make sure that your roof deck is done in accordance with the building code.

Now What?

When you’re putting a roof deck up, you’re going to want to be proactive and replace your waterproof membrane first. The energy code requires that you add insulation, which will add height to your roof and might make your parapets too low (to meet the code, they have to be 42 inches high). You have to deal with the Americans with Disabilities Act, as well, which requires equal roof access for all residents. That means you’ll have to bring an elevator up to your roof, which is quite costly.

Now you have to figure out your roof’s structural capacity. Can it handle the load of a public deck, or do you have to reinforce it? That would mean going into people’s apartments on the top floor. Or do you build a platform above the roof for the deck to rest on? If so, it, too, needs to be accessible. Then there’s combustibility. In a non-combustible building, 20 percent of the roof area can be combustible. Combustible materials are basically anything but concrete pavers. Many new buildings have roof decks. It’s an amenity that people want. Residents want to go up and sit on the roof, and they think it’s a simple process. But boards need to understand that it’s time-consuming and costly.