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Developable land comes at a premium in high-density cities. Soaring property values threaten historic properties while simultaneously giving developers incentive to push for greater heights. In some cities, such as New York, purchasing what are referred to as "air rights" from a neighbouring land owner allows the construction of taller and denser developments that can occupy the airspace above abutting lots.
Air rights are essentially a property's unused development potential. Where allowed, small-scale buildings occupying a site with considerable development potential can sign off their air rights to abutting property owners, and therefore, large sums of money are associated with the air rights agreements. For the developers that secure additional air rights, they can exceed maximum height and density restrictions on their own site by adding on the unused potential of their neighbours. This has been evidenced in New York projects from over the last decade like 432 Park Avenue, Central Park Tower, and One57.
Imagine two neighbouring sites with 400m² footprints on a block zoned to allow 8,000m² developments. One site contains a historically significant low-rise structure while beside it is a vacant lot awaiting redevelopment. The selling of air rights above the historic property to the owner of the empty lot would transfer the historic site's remaining 7,600m² of potential to the neighbouring property. This would lead to an almost doubled size of a building occupying the vacant site, up to 15,600m², allowing both property owners to profit from the acquisition while preserving some of the block's heritage.
Some air rights/density transfers have become controversial as developers in New York City have applied the rules to assemble maze-like extensions of their zoning lots, allowing significantly more density to be compiled on one part of the site, creating substantially larger towers. Sites such as 200 Amsterdam have been referred to as having been gerrymandered. While courts have found them to have been proper applications of the law, activists who find the results to be overbearing are looking for some restrictions to be put on the practice.
While the discussion about zoning air rights has historically been a New York issue, the so-called "Manhattanization" of other major cities around the world has sparked discussion of implementing similar practices elsewhere.
Such transfers are not allowed in Toronto. In Toronto, other factors like the Tall Buildings Guidelines, area studies, and now Major Transit Station Areas are used to determine how large a developer will be allowed to build.
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From 2015 to 2017, UrbanToronto and its sister publication, SkyriseCities, ran an occasional series of articles under the heading Explainer. Each one took a concept from Urban Planning, Architecture, Construction, or other topics that often wind up in our publications, and presented an in depth look at it. It's time to revisit (and update where necessary) those articles for readers who are unfamiliar with them. While you may already know what some of these terms mean, others may be new to you. We are publishing or updating and republishing Explainer on a weekly basis.
This week's Explainer is a refresh and expansion of an original that appeared in 2015.
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