The Seward Park Cooperative on Manhattan’s Lower East side turned down $54 million from a developer in exchange for 162,000 of air rights. After a long negotiation process, the proposal was put to a vote but did not get the necessary amount of shareholder support to pass. The developer will still build adjacent to Seward Park, but will build two towers of 17 and 20 stories instead of 20 and 33 stories.
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The Author- 
Brian Silvestry , a licensed real estate broker, has been selling residential and commercial real estate since 1999. He has sold in every neighborhood from Battery Park City to Washington Heights.
If your plan is to expand a Manhattan townhouse in a landmark district you will need to get approval from the Landmark Preservation Commission(LPC) before getting a Department of Buildings Permit. You should hire an architect who is familiar and has worked before with the LPC so that they can best advise you. Generally, you might be able to build an extension on the back of the house that will match what the LPC has approved for neighboring properties but they may or may not let you go as high as they did. Also, materials used in the renovation will influence their decision to approve or deny including down to the types of windows and colors of the window frames.
Putting a penthouse on the roof might also be acceptable but it can not be visible from the street. So you might have 3000 square foot of air rights left on an Upper West townhouse on park block but the likelihood that you will be able to use them all will be small.
The Author- Brian Silvestry , a licensed real estate broker, has been selling residential and commercial real estate since 1999. He has sold in every neighborhood from Battery Park City to Washington Heights.
News about the NYC real estate residential and commercial markets provided and interpreted by an industry veteran licensed since 1999. Brian Silvestry of BSRG Inc. Licensed real estate broker