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How can I add an outdoor terrace to my co-op—and raise my apartment's value?

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My co-op's living room has a wall of windows that look out onto a large roof, which is the top of a lower wing of our building. (The roof is parapet walled four feet high, typical NYC gravel, and has some vent fans, etc.) I'd like to turn one of the windows into a door and build out a deck, with an enclosing fence along one side, and the existing roof enclosing the rest. I think this could be readily anchored without harming the existing roof or interfering with its functions, and would significantly boost the apartment's value. Is this viable at all? If so, what's the best way to approach the neighbors and the board, and is there a way to know how much it will raise my apartment's value?


A new deck would most definitely raise your apartment’s value, but you’re going to face a lot of obstacles bringing your idea to fruition, say our experts.

“Send the managing agent a written request for the board to consider the concept of terracing a portion of the existing roof for your sole and exclusive use at its next directors meeting,” suggests Thomas Usztoke, vice president of Douglas Elliman Property Management. “The response should gauge whether the board would even entertain such a concept.”

The board will likely have a number of concerns and questions, says Jeff Reich, an attorney with Schwarz Sladkus Reich Greenberg Atlas LLP, including. but not limited to, “the ability of the existing roof to handle recreational use, the privacy of neighboring apartments, and potential noise issues.” The process of building your deck could potentially involve reinforcing the rooftop below, altering the setup of existing vents, and updating the waterproofing as well, notes David Yum, an architect who works with Bolster. It’s also likely the board will require you to shoulder all the costs associated with your requests (permit applications, appraisal, etc.), says Usztoke, even if the proposal is ultimately rejected by the Department of Buildings.

Another expense to consider here: There’s a good chance your maintenance charges will go up along with the value of your apartment. “The co-op will likely seek to exact its own value by adding shares to the apartment and a purchase price for the space by a professional appraisal,” says Usztoke, with you be footing the bill—all "without assurances that it will pass beyond the concept stage,” he adds. Still, says Reich, “beyond the practical concerns, the board may be swayed by the economic benefits that may result from the license, lease, or sale of the space.” (Reception to this kind of add-on will vary from board to board, but if it's architecturally viable and could generate higher values and extra money, you've likely got a good shot. "Present the scheme in a way that addresses the issues that may impact [the board], and how you will moderate those," Yum recommends.) 

As far as how much the deck would raise your apartment’s value (and your monthly maintenance), there are a number of factors to consider. “A finished roof deck with a direct connection [to the apartment] can add significant value to an apartment,” says Miller Samuel appraiser Jonathan Miller. (Miller has also written about the value add of outdoor space on his own site.) “Even roof rights for the future development of a deck can add value.”

But how much? Miller says that the price-per-square-foot value of your outdoor space can settle anywhere from 25 to 50 percent of the price per square foot of your apartment’s interior. (So if your apartment is valued at $1,000 PPSF, your deck could have a value of up to $500 PPSF, for instance.) Similarly, he says, your added shares are also likely to be valued at 25 to 50 percent value compared to the rest of the apartment. “So 100 shares at a 50 percent value relationship would be prorated on a 50 percent share per square foot basis for the terrace,” he explains.

The specific value will ultimately depend on things like the size of your deck, its views, and general desirability. “The devil is in the details,” says Miller. “A three-foot-wide wraparound terrace may have a lower value than a similar sized rectangular terrace just off the living room. A roof deck that is adjacent to a large noisy compressor or has a five-foot parapet that blocks any views may be worth less than a deck that provides expansive open views.”

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