There is a great demand for new development in the UK, whether to satisfy commercial needs, or to supply the housing market. However, as our cities become more congested, not only greenfield, but also brownfield plots become more rare. In addition, protections such as conservation area status, listed buildings and so on can make it difficult to clear sites for redevelopment. It has become more common therefore to consider developing below existing properties, in basements, and also above them.
Generally, the owner of a property will also own the rights to the air above the property that they could reasonably use (thus excluding the flight paths of aeroplanes). That is, they may, subject to planning permission, be able to develop above their property. However, these rights can be sold or leased, enabling the construction of ‘air-rights’ buildings. Typically, air-rights buildings are constructed above existing infrastructure such as roads or railways, or over buildings such as low-rise shopping centres that may have been developed when space was at less of a premium.
The first air-rights building in the UK was One Embankment Place, a commercial office building for PwC constructed above Charing Cross station and completed in 1991. Not only did it build above Charing Cross station, but its services and lifts pass through the station itself. Other air-rights buildings include; Alban Gate at London Wall; Broadgate in the City of London and the Cannon Place development above Cannon Street Station.
Air-rights buildings can be extremely complex, requiring negotiations with multiple owners and occupants, sometimes a requirement to keep existing facilities running, issues to do with structural disturbance, access, safety and security and so on. This has inevitable meant that air-rights buildings tend to be more expensive, they take longer and they are higher risk than simply building on the ground. However, following an initial spate of air-rights buildings in the 1990’s there is fresh interest because of the lack of availability of more straight-forward sites. In addition, there has been the development of reliable technologies that ensure sound and vibrations are not transferred from existing structures (such as railways) to new air-rights buildings.
In the USA, air rights can be traded as Transferrable Development Rights (TDR). The rights to construct to a certain level of density above an existing building (typically a heritage building such as a church) are traded with the owner of another plot, enabling them to develop a at greater density (or higher) than would otherwise have been permitted.
In 2014, a report by WSP, Building our way out of a crisis - Can we capitalise on London's public assets to provide homes for the future? suggested that building above public assets in London could provide space for up to 630,000 new homes.
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