Whether you’re designing, constructing or managing a building in New York City or subject to the International Building Code (IBC), an accessory use or accessory space has likely been mentioned during the process.

An accessory occupancy is a space that is ancillary to the main occupancy of the building or portion thereof. This area is intended to support the main occupancy in some way.

Accessory occupancies are constructed in accordance with whichever occupancy group they most resemble and cannot exceed 10% of that story’s total building area. In addition, the accessory occupancy is limited to the area limitations provided for that individual use. The main occupancy is restricted to the overall building and area limitations for that occupancy; the accessory is limited as a whole, an aggregate of all accessory occupancies, as well as limited individually based on height and area limitations.

If that isn’t confusing enough, most people then assume that accessory spaces are not factored into the floor area. Floor area and floor area ratios are calculated to meet both building and zoning requirements. Floor area is not to be confused with building area, however.

Building area is defined in the code as the area within the exterior walls, excluding shafts and courts. Floor area excludes additional spaces:

The floor area of a building is the sum of the grass area of each floor of the building, excluding mechanical space, cellar space, floor space in open balconies, elevators or stair bulkheads and, in most zoning districts, floor space used for accessory parking that is located less than 23 feet above curb level.  (New York City Zoning Resolution)

The major takeaway is that accessory parking is excluded from the floor area calculation, but this exclusion does not apply to all accessory spaces. Accessory areas, such as storage, must be calculated in the floor area. While a building might meet all of the building requirements per the New York City Building Code or IBC in height and area requirements, restrictions might still be imposed by the local zoning requirements.

For any additional questions or comments on this topic, please contact Milrose Consultants.