Calculates the floor area ratio as total floor area ÷ site area × 100 (%). Each zoning district has its own upper limit.
Explanation
The floor area ratio, yosekiritsu in Japanese, is the total floor area of a building divided by the area of its plot. Where the coverage ratio limits how far a building may spread, the floor area ratio limits how much it may stack. It is the number a city plan uses to decide how many people and how much activity a district should hold.
FAR=site areatotal floor area×100 (%) - Total floor area is the floor area of every storey added together.
- Site area is the plot, measured as a horizontal projection.
Example
Take the defaults, 180 m² of floor area on a site of 150 m².
150180×100=120 (%) The ratio is 120%. Exceeding 100% is not an error: two storeys of 90 m² on a 150 m² plot give 180 m² of floor. Anywhere buildings routinely run to two or three storeys, ratios above 100% are the norm. Note that Japan states the ratio as a percentage, where English-speaking countries often write the same idea as a plain multiple, so 200% and an FAR of 2.0 mean the same thing.
Notes
- Two limits apply, and the smaller one wins. The first is the figure the city plan assigns to the zoning district. The second is derived from the width of the road the plot faces, and it bites when that road is narrower than 12 m. A plot on a narrow lane may not be able to use its zoned allowance in full.
- The floor area used for the ratio is not always the raw sum. Parking, basements and the shared corridors of apartment blocks can be excluded up to set proportions when they meet the conditions. Confirm the details with an architect.
- The coverage ratio and the floor area ratio bind at the same time. Room under one does not mean room under the other.