Net floor area is the floor area actually occupied by a building’s users, excluding unoccupied accessory areas such as corridors, stairways, ramps, toilet rooms, mechanical rooms and closets.
The International Building Code defines net floor area this way and uses it to calculate occupant load for uses such as classrooms and assembly spaces, where the people are in the occupied rooms. Gross floor area is the larger number: all floor area inside the exterior walls, including the spaces net floor area leaves out.
Net, gross and leasable
- Net floor area. Occupied rooms only. Used for occupant load in some uses.
- Gross floor area. Everything inside the exterior walls. Used for building size limits and for many zoning calculations.
- Gross leasable area. The area tenants lease and occupy, common in retail. See gross leasable area.
- Net rentable area. A leasing measure for offices. See net rentable area.
Why it matters for parking
- Parking requirements are usually written as spaces per 1,000 square feet of a stated area. Applying a ratio written for gross floor area to net floor area, or the reverse, can change the required supply by 15 to 25 percent or more. See parking ratios.
- Parking demand studies should state which area basis they use, and compare benchmarks on the same basis.
The Parkonomics view
Area definitions look like housekeeping, but they move parking counts. Before accepting a requirement or a demand estimate, confirm whether it is per gross, net or leasable area. That one word can be worth dozens of stalls.
Related terms: Gross Floor Area, Gross Leasable Area, Net Rentable Area, Parking Ratios, Required Parking Spaces