ADU rules in Buffalo

Buffalo calls an ADU a 'Dwelling, Ancillary': a dwelling unit associated with and incidental to a principal dwelling on the same lot. Table 6A of the Green Code marks it permitted by right (no special use permit) in N-1D, N-1C, N-1S, N-2C, N-2E, N-2R, N-3C, N-3E, N-3R, D-R, D-M, D-E, D-S and D-C, and leaves it blank in the two single-family zones N-4-30 and N-4-50, so a detached backyard unit is simply not allowed there even though a single-unit dwelling is. In the neighborhood zones a detached ancillary dwelling must also meet the carriage house building type standards of §3.2.3, and Table 3A maps the carriage house only in N-1C, N-2C, N-2E, N-2R, N-3C, N-3E and N-3R. So the practical by-right detached ADU zones are those seven plus the D-R, D-M, D-E, D-S and D-C district zones, where Article 3 building types do not apply.

The Table 6A row for 'Dwelling, Ancillary' is the same whether the unit is detached or attached, so an attached, basement or internal ancillary unit is permitted by right in the same 14 zones and prohibited in N-4-30 and N-4-50. Only §6.1.2.B.1 and .2 are written for a 'detached ancillary dwelling' (the lower-height, smaller-footprint and carriage house rules), which leaves an attached or internal unit governed by the 1,000 square foot cap plus the principal building's own form standards. A conversion that simply produces two units in one structure is also readable as a 'Dwelling, Double Unit' under §6.1.2.D, which Table 6A permits in exactly the same 14 zones, so the zone answer is the same either way.

§6.1.2.B.1 is blunt: no ancillary dwelling may exceed 1,000 square feet of gross floor area, and a detached one must have a lower height in feet and a smaller footprint than the principal building on the lot. Height then comes from the carriage house standards: 2 stories in N-2C, N-2E, N-2R, N-3C, N-3E and N-3R, 3 stories in N-1C. Where an ancillary carriage house abuts an interior side or rear lot line in an N-2R, N-3R, N-4-30 or N-4-50 zone it is capped at 18 feet along that setback line, rising to a maximum of 24 feet only if it is pulled back one extra foot for every foot above 18. There is no lot-area gate: §3.2.1.E.3 says the N-2R (one unit per 1,250 sq ft) and N-3R (one unit per 1,500 sq ft) residential density standard must not be interpreted as applying to an accessory dwelling.

Chapter 496 imposes no owner-occupancy condition on ancillary dwellings; the phrase 'owner-occupied' does not appear anywhere in the 342-page ordinance, and §6.1.2.B conditions the use only on the unit being incidental to a principal dwelling on the same lot. Owner occupancy matters only downstream in other chapters: §264-3.B exempts owner-occupied properties with two or fewer dwelling units from rental dwelling unit registration, and §380-7.A allows owner-occupied short-term rentals as of right in most zones while requiring a special use permit for non-owner-occupied ones. New York has no statewide ADU statute that would preempt or add to this; Buffalo's zoning power comes from General City Law and the Municipal Home Rule Law (§1.1.3).

The Green Code abolished off-street parking minimums citywide when it took effect in 2017, and §8.3.1.A still reads that there are no provisions establishing a minimum number of off-street parking spaces for development. The only backdoor is the transportation demand management plan of §8.4, and that is triggered only by new construction of a principal building over 5,000 square feet or a substantial renovation of at least 50,000 square feet involving a change of use, with single-unit and double-unit dwellings expressly excluded, so an ADU never triggers one. Parking you choose to build still has to meet the stall, aisle and surfacing standards of §8.3.

Every zone where Table 6A allows an ancillary dwelling shows the 'permitted' symbol, not the 'special use permit required' symbol, so there is no discretionary hearing. The path is administrative: register the project with the Department of Permit and Inspection Services under §11.2.1.A, which identifies the approvals and forms, then obtain a building permit. Site plan review is keyed to principal buildings, so a backyard carriage house accessory to an existing house falls below both thresholds (§11.3.6.C covers new construction of a principal building, a 2,500 sq ft addition to one, and similar; §11.3.7 starts at 5,000 sq ft). The exception is a carriage house that is itself the principal building on an alley-fronting lot, which is new principal-building construction and does go through minor site plan review by the Zoning Administrator.

Nothing in Chapter 496 restricts renting an ancillary dwelling long term, and there is no primary-residence test. Under Chapter 264 a rental dwelling unit registration certificate is required before renting, but owner-occupied properties containing two or fewer dwelling units are exempt, so an owner living in the house and renting the ADU generally does not register. Short-term rental is governed by Chapter 380, adopted 2-20-2024: a license and annual inspection are required, owner-occupied short-term rentals are allowed as of right everywhere except N-4-30, N-4-50, D-IL, D-IH, D-OS, D-OG, D-ON and C-R, non-owner-occupied ones need a §11.3.3 special use permit and a two-night minimum stay, no more than two dwelling units per building may be short-term rented, and local historic districts get extra written findings. The unit cannot be sold separately because §6.1.2.B requires it to sit on the same lot as the principal dwelling.