Guide
How to calculate the floor area ratio in single-dwelling zones.
Floor Area Ratio
Floor area is the total area of all floors of a building. Also:
- Floor area is measured for each floor from the exterior faces of a building or structure.
- Garages and other enclosed structures also count as floor area.
- Lofts and portions of a house with vaulted ceilings are only counted as floor area for the area of the additional floor.
- Bays and bay windows are counted toward floor area if they extend to a finished floor or have a step acting as an additional floor.
- Portions of buildings that are below ground or with lower ceilings may or may not count as floor area.
How to calculate Floor Area Ratio
Floor area ratio is a relationship between the size of a lot and the size of allowed development on the lot. For example:
Example of Floor Area Ratio
Areas included in Floor Area Ratio
- Portions of a house with vaulted ceilings are counted as floor area only for the lower level with the floor.
- Lofts are included as floor area only for portions with additional floor and a ceiling height of 6 feet, 8 inches.
- Stairs that lead from one story of a house to another story count toward floor area one time (not at both levels).
- Bays and bay windows are counted toward floor area if they extend to the adjacent finished floor and have a ceiling height of 6 feet, 8 inches.
Areas not included in Floor Area Ratio
- Basements that are partly or completely below grade. At least half of the total combined area of the basement walls must be below grade to be considered a basement. Only one basement level may be partly below grade; additional basement levels must be completely below grade.
- Areas where the ceiling height is less than 6 feet, 8 inches such as dormers or attics
- Sloped sites, areas where the elevation of the floor is 4 feet or more below the adjacent right-of-way
- Covered porches or balconies are not included unless they are enclosed by walls that are more than 42 inches high for 75 percent or more of their perimeter.
- Rooftop decks do not count toward floor area if they are not covered or enclosed.