Can you build an ADU in Tonawanda, NY?

R-1 Single-Family Residential - The side yard is asymmetric: a house owes at least 2 ft on one side and at least 6 ft on the other, and which side takes the 6 ft is fixed for every lot on a street in a block rather than by the builder. Building 2 ft on both sides does not comply.

• Only a single-family dwelling is permitted, and a two-family is not available at any lot size, though an accessory dwelling unit or in-law suite is reachable by special permit under § 215-24.3
• The lot area and the lot width may instead be met by the average lot area or width on the block
• Where 20% of the lots in a single block are improved with buildings on a uniform line, that average becomes the established building line and displaces the front setback shown
• The coverage figure counts structures and impervious surfaces together, so driveways and parking consume it alongside the building
• A minimum open space of 40% in grass, landscaped or natural area applies
• A dwelling of two or more storeys must have a building footprint of at least 520 sq ft, against 800 sq ft for a one-storey dwelling

R-2 Two-Family Residential - A two-family dwelling is permitted by right on the same 4,500 sq ft as a single-family, so the second unit costs no additional land and no approval. The side yard is asymmetric: at least 2 ft on one side and at least 6 ft on the other.

• Which side takes the 6 ft is fixed for every lot on a street in a block rather than by the builder, and building 2 ft on both sides does not comply
• The lot area and the lot width may instead be met by the average lot area or width on the block
• Where 20% of the lots in a single block are improved with buildings on a uniform line, that average becomes the established building line and displaces the front setback shown
• The coverage figure counts structures and impervious surfaces together, so driveways and parking consume it alongside the building
• A minimum open space of 40% in grass, landscaped or natural area applies
• Accessory structures take 2 ft side and rear yards and a 12 ft height cap, rising to 16 ft for a private garage, and a garage is capped at 900 sq ft of footprint

MR Mixed Residential - A multi-family dwelling of up to four units is permitted by right, by conversion or new construction. Above four units is permitted too, but converting a single- or two-family dwelling to more than four units is prohibited, so a larger building must be built as one.

• The side yard is asymmetric: at least 2 ft on one side and at least 6 ft on the other, with the larger side fixed for every lot on a street in a block
• The lot area and the lot width may instead be met by the average lot area or width on the block
• Where 20% of the lots in a single block are improved with buildings on a uniform line, that average becomes the established building line and displaces the front setback shown
• The coverage figure counts structures and impervious surfaces together, so driveways and parking consume it alongside the building
• A minimum open space of 50% in grass, landscaped or natural area applies
• Senior housing and a community centre are permitted by right, and a mobile home park by special permit

MU-N Mixed Use Neighborhood - The front setback shown is a minimum with a 20 ft maximum on top of it: a building may sit on the front lot line, and one set back more than 20 ft does not comply. That build-to rule rules out a parking-in-front layout.

• A nonresidential primary structure may not exceed 5,000 sq ft of building footprint, a private garage 900 sq ft and any other enclosed accessory building 180 sq ft
• That 5,000 sq ft footprint cap is what binds a commercial building here, well before the coverage figure does
• The minimum lot area is tiered by use: at least 4,500 sq ft for a single- or two-family dwelling, 2,000 sq ft per unit for multifamily, and 10,000 sq ft for any other use
• The minimum lot width is 50 ft for a residential use and 70 ft for any other
• The side setback rises from 5 ft to 10 ft where the lot is adjacent to a residential use or district
• The coverage figure counts structures and impervious surfaces together, and a minimum open space of 15% in grass, landscaped or natural area applies

MU-GC Mixed Use General Commercial - The front setback shown is a minimum with a 50 ft maximum on top of it, so a building must hold a front yard but may not sit deeper than 50 ft from the front line, and a deep parking apron in front of the building is not permitted.

• The minimum lot area is tiered by use: at least 6,500 sq ft for a single- or two-family dwelling, 2,000 sq ft per unit for multifamily, and 15,000 sq ft for any other use
• The minimum lot width is 50 ft for a residential use and 70 ft for any other
• The side setback rises from 5 ft to 15 ft where the lot is adjacent to a residential use or district
• The limits of 45 ft and three storeys both apply, so a four-storey building does not comply even under 45 ft
• The coverage figure counts structures and impervious surfaces together, so driveways and parking consume it alongside the building
• A minimum open space of 15% in grass, landscaped or natural area applies

MU-W Mixed Use Waterfront - The side and rear setbacks, the coverage cap and the building height are all set through site plan review by the Planning Board, so a pre-application conversation is the only way to get a figure for the buildable envelope on a waterfront parcel.

• The front setback shown is a minimum with a 50 ft maximum on top of it
• The lot area for multifamily and for any other use is also set through site plan review
• The minimum lot width is 60 ft for a residential use and 70 ft for any other
• A minimum open space of 35% in grass, landscaped or natural areas applies, and with coverage set through site plan review it is the one fixed density limit here
• A separate shoreline setback applies to a water-facing frontage and is also settled through site plan review
• The Local Waterfront Overlay under § 215-23 may apply on top of the district

MU-I Mixed Use Industrial - A minimum open space of 35% in grass, landscaped or natural area applies, the exact complement of the coverage cap, and on a large-footprint building or a truck yard it is the standard most likely to bind, well before the height limit does.

• The side setback rises from 10 ft to 25 ft where the lot is adjacent to a residential use or district
• The rear setback is stated flat, with no step for a lot adjacent to a residential use or district
• Accessory yards are 5 ft, rising to 15 ft on the same test, and accessory structures are held to 25 ft in height
• The coverage figure counts structures and impervious surfaces together, so driveways and parking consume it alongside the building
• The lot area and the lot width are stated flat, with no tiering by use

GI General Industrial - The side and rear setbacks shown are the base figures: each rises to 50 ft where the lot is adjacent to a residential use or district, so a parcel that backs onto housing must hold 50 ft on that boundary.

• Accessory yards are 5 ft, rising to 25 ft where the lot is adjacent to a residential use or district
• Accessory structures are held to 25 ft in height
• The coverage figure counts structures and impervious surfaces together, so driveways and parking consume it alongside the building
• A minimum open space of 25% in grass, landscaped or natural area applies

CF Community Facility - A minimum open space of 35% in grass, landscaped or natural area applies, the exact complement of the coverage cap, and on a school or church site with a large parking requirement it is usually the standard that binds first.

• The side setback rises from 10 ft to 25 ft where the lot is adjacent to a residential use or district
• Accessory yards are 5 ft, rising to 10 ft on the same test
• The limits of 45 ft and three storeys both apply
• The front setback is stated flat, with no maximum on top of it
• The coverage figure counts structures and impervious surfaces together, so driveways and parking consume it alongside the building

OS Open Space - A minimum open space of 85% in grass, landscaped or natural area applies, the exact complement of the coverage cap shown, and that cap counts structures and impervious surfaces together rather than building footprint alone.

• No minimum lot area and no minimum lot width are set for this district
• The front setback is stated flat, with no maximum on top of it
• The side setback is stated flat, with no step for a lot adjacent to a residential use or district
• Accessory yards are 5 ft, rising to 10 ft on the same test
• The limits of 35 ft and two and a half storeys both apply