Floor area ratio

Floor area ratio, universally FAR, is total building floor area divided by lot area. A 2,000 square foot house on a 10,000 square foot lot has an FAR of 0.2.

FAR limits total building size in a way lot coverage does not, because it counts every floor. A two story building can meet a coverage limit comfortably while exceeding the FAR cap.

What counts as floor area

Definitions vary and the differences are significant:

• Above-grade conditioned space essentially always counts
• Basements and cellars sometimes count, sometimes do not, sometimes count only when above a certain height out of the ground
• Garages are treated differently in different places, and are sometimes exempt up to a size
• Covered but unenclosed space, like porches, is often excluded
• Attic space is often excluded below a headroom threshold

Because the definition varies this much, an FAR calculation is only meaningful against the local ordinance's own definition.

Where it is used

FAR is more common in dense urban zoning and in commercial districts than in low-density residential ones, where coverage, setbacks, and height do most of the work. Where it does apply to houses, it is usually there to control the scale of teardown-and-rebuild projects relative to their neighbors.