What it costs to build an ADU in Bronxville, NY

One-Family Residence AAA District - Floor area is set by a schedule keyed to lot size rather than one ratio for the district, running from 0.490 below 5,000 sq ft to 0.190 above 39,000 sq ft and interpolated between the printed lot sizes (§ 310-22E).

• At least 60% of the lot must stay open space (§ 310-8H).
• The 17.5% building coverage cap counts every principal and accessory building on the lot.
• The 40 ft front yard applies along each street line, so a corner lot owes one on each street.
• Without a garage, one side yard must be at least 30 ft.
• On a corner lot, the yard opposite the principal front yard must be at least 30 ft.
• Where the walls facing the street meet the street line at 25 degrees or more the building may come to within 20 ft, and the lesser side setback may be cut by 5 ft, but not without a garage (§ 310-8D).

One-Family Residence AA District - Floor area is set by a schedule keyed to lot size rather than one ratio for the district, running from 0.490 below 5,000 sq ft to 0.190 above 39,000 sq ft and interpolated between the printed lot sizes (§ 310-22E).

• At least 55% of the lot must stay open space (§ 310-9H).
• The 35 ft combined side yard applies on any lot other than a corner lot.
• Without a garage, one side yard must be at least 27 ft.
• On a corner lot, the yard opposite the principal front yard must be at least 30 ft and the other at least 15 ft, or at least 27 ft without a garage.
• Where the existing front yards of dwellings within 300 ft on the same street average under 35 ft, the front yard may shrink to that average, but not below 25 ft.
• Where the walls facing the streets meet the street line at 25 degrees or more, the front yard may be cut to 25 ft and the lesser side setback by 5 ft (§ 310-9D).

One-Family Residence A District - Floor area is set by a schedule keyed to lot size rather than one ratio for the district, running from 0.490 below 5,000 sq ft to 0.190 above 39,000 sq ft and interpolated between the printed lot sizes (§ 310-22E).

• At least 55% of the lot must stay open space (§ 310-10H).
• Without a garage, one side yard must be at least 27 ft.
• On a corner lot, the yard opposite the principal front yard must be at least 30 ft and the other at least 15 ft, or at least 27 ft without a garage.
• Where the existing front yards of dwellings within 300 ft on the same street average under 30 ft, the front yard may shrink to that average, but not below 25 ft.
• Where the walls facing the streets meet the street line at 25 degrees or more, the front yard may be cut to 20 ft and the lesser side setback by 5 ft (§ 310-10D).
• Off-street parking is one space per dwelling (§ 310-10F).

Two-Story Multiple Residence B District - This is a multiple residence district, and each dwelling unit needs 2,750 sq ft of land on a lot of at least 12,000 sq ft, so land is what caps the unit count rather than a printed density (§ 310-11C).

• Each dwelling unit also needs 400 sq ft of usable open space (§ 310-11E).
• Building length is capped at 160 ft (§ 310-11G).
• The 100 ft depth is an average depth, not a minimum at every point.
• The 12,000 sq ft applies to every permitted use, including a one-family dwelling.
• A side yard may be eliminated along a lot line where the adjoining lot is built to that line, provided the other side yard is doubled (§ 310-11D(4)(b)).
• Where the Planning Board finds under-building or roof-deck parking impractical it may allow accessory garages by special permit to cover an additional 10% of the lot (§ 310-11F).

Three-Story Multiple Residence C District - Each side yard must be at least half the height of the wall facing the side lot line, with 12 ft only as the floor, so a taller building needs a wider yard (§ 310-12D(2)).

• This is a multiple residence district, and each dwelling unit needs 1,750 sq ft of land on a lot of at least 12,000 sq ft, so land caps the unit count.
• Each dwelling unit also needs 400 sq ft of usable open space (§ 310-12E).
• Building length is capped at 160 ft (§ 310-12G).
• The 100 ft depth is an average depth, not a minimum at every point.
• A side yard may be eliminated along a lot line where the adjoining lot is built to that line, provided the other side yard is doubled (§ 310-12D(4)(b)).
• Where the Planning Board finds under-building parking impractical it may allow accessory garages by special permit to cover an additional 10% of the lot (§ 310-12F).

Six-Story Multiple Residence D District - The side yard is half the height of the facing wall up to 36 ft of building, then 25 ft plus one sixth of that wall's height above 36 ft, with 12 ft only as the floor (§ 310-13D(2)).

• This is a multiple residence district, and ordinary multifamily needs 1,500 sq ft of land per dwelling unit on a lot of at least 12,000 sq ft, so land caps the unit count.
• An age restricted multiple residence facility is a separate set of standards: a lot of at least 60,000 sq ft, 750 sq ft of land per dwelling unit and 600 ft of street frontage (§ 310-13C(2)).
• Its yards differ sharply too: 5 ft in front, 60 ft on each side and 12 ft at the rear, against 20 ft, 12 ft and 30 ft for everything else (§ 310-13D(5)).
• That age restricted facility may cover up to 55% of the lot against 25% for everything else, is capped at 90 dwelling units, and may give no more than 20% of its gross floor area to auxiliary use.
• Each dwelling unit needs 300 sq ft of usable open space, and building length is capped at 180 ft, which an age restricted building may exceed only on Planning Board site plan review.
• Where the Planning Board finds under-building parking impractical it may allow accessory garages by special permit to cover an additional 10% of the lot (§ 310-13F(1)).

Central Business A District - No yard of any kind is required, but a yard that is provided must be at least 6 ft (§ 310-14D(5)).

• Height is a band and not only a ceiling: no more than two storeys and 32 ft, but also not less than 15 ft above the average elevation at the building line (§ 310-14D(6)(a)).
• On a lot of 2,500 sq ft or less the floor area ratio may rise to 1.6, at the Planning Board's discretion (§ 310-14D(3)).
• No single use may occupy more than 3,500 gross sq ft of floor area at the principal street level, raised to at most 5,000 by special permit (§ 310-14D(2)).
• A principal permitted use may occupy no more than 35 linear ft of street frontage, raised to at most 50 by special permit (§ 310-14D(4)).
• One dwelling unit may not exceed 2,000 gross sq ft, raised to at most 6,600 by special permit (§ 310-14A(8)(b)).
• Residential use is barred at street level, so dwellings sit above the street floor only (§ 310-14A(8)(a)).

Service Business B District - No yard of any kind is required, but a yard that is provided must be at least 6 ft (§ 310-15D(3)).

• Height is three storeys and 42 ft above curb level, and a basement is not counted as one of the three storeys (§ 310-15D(4)(a)).
• Where the lot fronts two nonintersecting through streets, height is measured from the higher curb level only (§ 310-15D(4)(b)).
• Rooftop structures count toward height once they rise more than 12 ft above the adjoining roof or cover more than 20% of the roof (§ 310-15D(4)(c)).
• Such a structure must also stand back 10 ft from the front and rear walls and 3 ft from the side walls, except elevator and stair enclosures the plan of the building requires (§ 310-15D(4)(d)).