Why Floor Area Moves Only Between Lots That Touch
By Michael Stern, JDS Development Group
Two lots on the same block each hold floor area they will never use, and a third lot sits between them. That third lot decides whether either of the first two can ever contribute to a tower, because under the general rule floor area moves only between lots that form a single zoning lot, and a zoning lot has to be contiguous. This is written for developers and land use professionals evaluating an assemblage, and for anyone who has looked at a block map and wondered why a small site can hold a tall building while a larger one nearby cannot.
What a zoning lot is and why it is the unit that matters
Floor area is counted on the zoning lot, a unit the zoning creates for its own purposes, which can be one tax lot or several tax lots treated as one under the rules. The deed map and the zoning map therefore disagree by design. The deed map shows who owns what, the zoning map shows what may be built where, and the zoning lot is the bridge between them.
The Department of City Planning keeps a plain language definition of the zoning lot in its zoning glossary, and it is worth reading slowly, because every quantity a site is evaluated on flows from it. The permitted floor area of a zoning lot is its area multiplied by the ratio the district allows, and whatever already stands on it has consumed part of that. What remains is the unused area, and unused area is what people mean when they say air rights.
What actually transfers, and what does not, is a subject of its own. The narrower question here is where that area is allowed to go, and the answer is shorter than most people expect.
How floor area moves between lots that touch
The zoning lot merger
The ordinary route is a merger. Two or more contiguous tax lots are declared, by recorded instrument, to be a single zoning lot, and from that moment the floor area of the combined lot is computed as one number and may be located anywhere on it that the envelope rules permit. Each tax lot keeps its own deed and its own owner, and the zoning simply stops seeing the line between them.
The declaration is recorded against every lot in the merged zoning lot and binds every future owner of each of them. That permanence is the part developers underestimate. A design can be revised for years, and the declaration outlasts all of them.
What contiguity means on a real block
Contiguous means the lots share a boundary, and the rule is unforgiving about it. A lot across a public street does not touch. A lot separated by one narrow parcel does not touch, however much area it has to spare, and it contributes nothing to the assemblage until that parcel joins the zoning lot as well.
A chain of lots is only as long as its unbroken run of shared boundaries. A public street breaks the chain, while a strip of land that is itself a lot does not, and joining that strip is sometimes the whole project. The geometry of the block, the position of the alleys, the odd L shaped parcel that reaches around a corner, decides that run before anyone has asked what any lot holds.
The map that matters to a tower is a map of who touches whom, and it is a different map from the one that shows who has area to spare.
This is why an assemblage is drawn as a chain rather than gathered as a pool. The area a site can reach is the sum of what sits along an unbroken run of lot lines back to it, and nothing else on the block counts, whatever it holds. On a constrained Manhattan site that arithmetic is finished long before an architect is engaged, which is the ordinary reason the shape of a tower is decided before its design is.
111 West 57th Street rose in the courtyard of the landmarked Steinway Hall. A courtyard is the purest case of the rule, because by definition it is reached only by what surrounds it, and on a site like that the question of adjacency comes before any question of design.
When floor area can cross a street
The general rule has exceptions, and they matter because they are the routes that let area travel where a merger cannot carry it. The best known is the landmark route. A designated building that will never grow taller holds unused area with nowhere to go, and preservation law gives it a path of its own to nearby lots, including across a street, under conditions the zoning and the Landmarks Preservation Commission set.
Certain special districts write their own routes as well, letting area move within a defined part of the city under rules of their own, and those rules live in the text of the Zoning Resolution rather than on any map. Which route a given lot can use is a question of the current text and of the designations in force on that block, and both change. Land use counsel confirms it against the text on the day it matters, and I would trust nothing else.
Why the contiguity map beats the unused area map
Here is the position a competent peer could argue with. Given the choice, I would rather hold a small lot with the right neighbors than a large lot with none, because the large lot has already shown me its ceiling and the small one has not. Most developers evaluate a site by its own permitted area first and its neighbors second, and on a constrained block I think that order is backward.
The counterargument is real. A large lot holds a real building on its own, while a chain is a sequence of events that may never complete, so the small lot is a bet on geometry and on time. I accept that bet more often than most, and I have been wrong about it.
The honest limit is time. A chain is assembled one recorded instrument at a time, in whatever order the block allows, and no amount of effort compresses the sequence. A site that touches the right lots can still take longer to become a single zoning lot than the building takes to rise on it afterward.
None of this is advice. The declaration is drafted by real estate counsel and recorded through a title company, the contiguity of a specific set of lots is read from a survey and confirmed by a zoning consultant, and the route a landmark or a special district offers is confirmed by land use counsel against the text in force. What a developer brings is the block map, read the right way around.
Read the lot lines before the floor area, because a tower is built out of the lots it touches.
Michael Stern is the founder and chief executive officer of JDS Development Group.
