Codes & Regulations
Zoning arithmetic and code thresholds
Most regulation questions reduce to arithmetic plus one precise definition. In zoning, know permitted uses and conditional uses, setbacks (front, side, rear), height limits (in feet and in stories), lot coverage, floor area ratio (FAR), density (units per acre), parking and loading minimums, open space, and design review or historic overlays.
In the building code, know occupancy classification and how a mixed occupancy is handled, occupant load factors, egress (number of exits, travel distance, common path, egress width), construction type with allowable height and area - including increases for sprinklers and frontage - fire separation, and accessibility: accessible route, clear floor space, door clear width, ramp slope of 1:12 with landings, and reach ranges. Fair Housing and local environmental overlays round out the set.
Traps
- FAR vs lot coverage: FAR limits total gross floor area over the whole lot; lot coverage limits only the footprint.
- Excluded areas from gross floor area (below-grade parking, some mechanical space) are defined locally - check before you compute.
- Height in stories is not the same as height in feet.
- Occupant load factors differ between gross and net floor area.
Worked example
30,000 sf lot, FAR 2.0, 50% lot coverage, 60 ft height limit, 12 ft floor-to-floor. FAR allows 60,000 sf. Coverage allows a 15,000 sf footprint. Five floors would be 75,000 sf, so FAR governs: four floors at 15,000 sf = 60,000 sf, or a smaller footprint with more floors up to the 60 ft limit.