Ann Arbor, Michigan: Virtual Downtown Experiments

Abstract

The problem of where to locate tall buildings, with sensitivity to existing building types on adjacent and nearby lots, is a difficult one. In Ann Arbor, building height is currently limited by "floor area ratio" (FAR). The FAR is calculated as the ratio of floor area in a building divided by parcel area, times 100. If a given parcel has an FAR of 100, then a building footprint built lot line to lot line may have a height of 1 story. If a parcel has an FAR of 200, then a building footprint built lot line to lot line may have a height of 2 stories. Similarly, an FAR of 300 yields a building of height 3 stories covering the entire parcel. Thus, on a parcel with an FAR of 300, one might, instead, build a building on half of the lot area but of height six stories, or on a third of the lot area but of height 9 stories. On the same parcel, a 30 story building could be built only if its footprint covered one-tenth of the land area of the parcel. The FAR provides a height limit based on the size of foundation needed to support a tall building. It also offers subtle encouragement for preserving some amount of open space and visual variation in the region to which it applies. The drawback is that a tall building may get built with no regard to the broader context of how a new building will fit in with existing buildings on the surrounding parcels. A possible side effect of using FAR (alone) to limit height is that it might encourage parcel amalgamation by large developers, thereby driving out desired local small business owners.