The short answer: Yes, if your home isn’t landmarked or in a historic district. If it isn’t, you’re limited only by zoning regulations, which dictate how big your house can be and how high it can go if you’re considering an extra floor. The only brake on your creativity is your willingness to infuriate the neighbors.
If your house is landmarked or (more likely) in a historic district—and there are dozens of these areas in the city, easily spotted by their white-on-brown street signs—the rules get trickier. (To find out if yours is, call the Landmarks Preservation Commission at 212-669-7817.) Before you can do any work on the exterior—anything from adding a mailbox to repainting the façade—you must submit architectural plans to the LPC for review. “Because there are so few and they are generally survivors from long ago, [houses] are looked at closely,” says Prudential Douglas Elliman managing director Bruce Ehrmann, who co-chairs the Landmarks Committee of Community Board 1. LPC staff can help guide your vision and let you know if it’s “realistic to pursue,” he says.
For significant alterations (more than, say, painting), a hearing will typically follow with members of your local community board, who’ll approve, reject, or suggest alterations to make your changes in context with the neighborhood. The entire community board will then vote yes or no on your renovation plans, and forward their decision to the LPC, which will hold a public hearing. (Expect your neighbors to voice their opinions—and loudly.) The commission will then make a ruling. It’ll take up to six months from the time you submit your plans to the final decision.
As for the interior, you’re in the clear, unless it’s landmarked, too. (That’s rare: Only about 5 percent of landmarked houses have landmarked interiors.) Renovations to the back of the house are almost always less cumbersome, as are rooftop extensions, as long as they’re not visible from the street.