Air rights

Air rights is the market's name for a lot's unused development rights: the difference between the floor area its zoning allows and the floor area actually built, expressed in square feet. The term is a metaphor — what trades is not literally the air but the transferable floor-area budget, which moves between lots through zoning-lot mergers, landmark transfers under § 74-79, or the transfer mechanisms of particular special purpose districts.

Air rights have value because dense-market development is constrained by floor-area budgets: a developer whose site cannot legally hold the intended building buys the shortfall from neighbors. For the seller, the rights monetize headroom without altering the existing building — though the sale permanently encumbers the lot, binding future owners to the reduced budget.