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ADU · Westchester County

Can you build an ADU in New Castle, NY?

Town of New Castle has 17 districts. 9 districts prohibit ADUs, 8 allow them with occupancy restrictions. Check your address to confirm the district that applies to your parcel:

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What the New Castle code says

One accessory apartment is allowed per one-family lot in the one-family residence districts, with site development plan approval rather than a special permit, if an owner of the lot lives in one of the units as a principal residence (§ 60-420B(5)).

Conditions the code attaches:

What the New Castle code indicates by district

The table below shows how each district treats ADUs, alongside the lot and setback standards that govern a second unit. District boundaries and conditions vary, so treat this as a starting point and confirm the district that applies to your parcel.

District Min lot Setbacks F / S / R Max height ADU
Multifamily Planned Development District 5 ac 50 / 20 / 20 ft 35 ft No
One-Family Residence District 2 ac 75 / 45 / 60 ft 35 ft Occupancy restricted
One-Family Residence District 2 ac 75 / 45 / 60 ft 35 ft Occupancy restricted
Multifamily Residence District - Chappaqua 1 ac 50 / - / - ft 35 ft No
Multifamily Residence District - Millwood 1 ac 50 / 15 / 15 ft 35 ft No
One-Family Residence District 0.5 ac 50 / 20 / 40 ft 35 ft Occupancy restricted
One-Family Residence District 0.5 ac 50 / 20 / 40 ft 35 ft Occupancy restricted
One-Family Residence District 1 ac 60 / 35 / 50 ft 35 ft Occupancy restricted
One-Family Residence District 1 ac 60 / 35 / 50 ft 35 ft Occupancy restricted
One-Family Residence District 1 ac 60 / 35 / 50 ft 35 ft Occupancy restricted
One-Family Residence District 0.26 ac 40 / 10 / 35 ft 35 ft Occupancy restricted
Research and Office Business 20 ac 150 / 300 / 300 ft 40 ft No
Designed Business — 10 / 0 / 20 ft 30 ft No
Retail Business — 10 / 0 / 0 ft 35 ft No
Retail Business and Parking — 10 / 0 / 0 ft 35 ft No
General Industrial 0.17 ac 25 / 8 / 20 ft 30 ft No
Planned Industrial 15 ac 100 / 100 / 100 ft 30 ft No

Multifamily Planned Development District - Density is set by land per dwelling unit: at least 4,400 sq ft for an efficiency, 6,600 for one bedroom, 8,800 for two, 11,000 for three, and 13,200 for four bedrooms or a one-family detached dwelling.

  • The five acres is the whole development, and lots inside a development subdivided on a Planning Board plan have no minimum.
  • Where the lot adjoins a one-family residence district, the side and rear yards must be at least 30 ft or one and one-half times the height of the building, whichever is greater.
  • Coverage counts nonwetland area plus 33% of wetland area and excludes parking wholly underground, and wetland area counts at one third toward density.
  • The board approving the concept plan may grant an incentive increase above that density.
  • Each dwelling unit needs at least 450 sq ft of floor area for an efficiency, 650 for one bedroom, 750 for two, 1,000 for three and 1,200 for four.
  • Three- and four-bedroom units must have at least one and one-half baths.

One-Family Residence District - Building coverage, development coverage and floor area are capped in square feet on a sliding scale by lot area. On a lot of 87,120 sq ft or more, buildings may cover 5,739 sq ft plus 2% of the area above 87,120 sq ft.

  • Development coverage on such a lot is 13,098 sq ft plus 7% of the area above 87,120 sq ft, counting all buildings and structures, including driveways, parking areas, walks, decks and terraces.
  • Floor area, counting half of garage and basement floors, is capped at 7,841 sq ft on a lot of 87,120 to 98,010 sq ft, rising in steps to 10,193 sq ft below 196,020 sq ft.
  • A lot holding a single-family affordable AFFH unit needs 75% of the lot area, and one holding a two-family affordable AFFH unit needs the one-family lot area.
  • No more than 10% of the minimum lot area may be under water, floodway or wetland.
  • A yard equal to the front yard is required along every lot line that abuts a street, and no accessory building, deck, porch or terrace may stand in a required yard.
  • A multifamily designed residential development needs a Planning Board special permit and a site at least 100 times the one-family lot minimum, at 10% building and 20% development coverage.

One-Family Residence District - A lot lying in both R-2A and R-1A must meet the most stringent lot area, setbacks, building coverage and development coverage of either (§ 60-330), and R-2A ranks as the more restrictive, so its figures apply.

  • On a lot of 87,120 sq ft or more, building coverage is capped at 5,739 sq ft plus 2% of the area above 87,120 sq ft.
  • Development coverage on such a lot is 13,098 sq ft plus 7% of the area above 87,120 sq ft, counting all buildings and structures, including driveways, parking areas, walks, decks and terraces.
  • Floor area, counting half of garage and basement floors, is capped at 7,841 sq ft on a lot of 87,120 to 98,010 sq ft, rising in steps to 10,193 sq ft below 196,020 sq ft.
  • No more than 10% of the minimum lot area may be under water, floodway or wetland.
  • A yard equal to the front yard is required along every lot line that abuts a street, and no accessory building, deck, porch or terrace may stand in a required yard.
  • A multifamily designed residential development needs a Planning Board special permit and a site at least 100 times the one-family lot minimum, at 10% building and 20% development coverage.

Multifamily Residence District - Chappaqua - Basic density, by right with site plan approval, is set by land per dwelling unit: at least 2,200 sq ft for an efficiency, 3,300 for one bedroom, 4,400 for two, 5,500 for three, and 6,600 for four bedrooms or a one-family detached dwelling.

  • A Planning Board special permit may raise that density by up to 100% for incentive features such as affordable, senior, handicapped or rental units, underground parking or recreation facilities.
  • A development of five to nine units must include one affordable AFFH unit, and one of 10 or more units at least 10%.
  • Every unit must connect to public water and sewer.
  • The one acre is the whole development, and lots inside a development subdivided on a Planning Board plan have no minimum.
  • Coverage counts nonwetland area plus 33% of wetland area and excludes parking wholly underground, and wetland area counts at one third toward density.

Multifamily Residence District - Millwood - Where the lot adjoins a one-family residence district, the side and rear yards must be at least 25 ft or the height of the building, whichever is greater.

  • Density is set by land per dwelling unit, at least 3,300 sq ft for an efficiency, 4,950 for one bedroom and 6,600 for two, by right with site plan approval.
  • It is at least 8,250 sq ft for a three-bedroom unit and 9,900 for four bedrooms or a one-family detached dwelling.
  • A Planning Board special permit may raise that density by up to 100% for incentive features such as affordable, senior, handicapped or rental units, underground parking or recreation facilities.
  • A development of five to nine units must include one affordable AFFH unit, and one of 10 or more units at least 10%.
  • Sites are to be served by public or community water and sewer.
  • The one acre is the whole development, and lots inside a development subdivided on a Planning Board plan have no minimum.

One-Family Residence District - Where there is no municipal water main within 200 feet of the existing or proposed building, the minimum lot reverts to the R-1A requirement of one acre.

  • On a lot of 21,780 to 43,560 sq ft, building coverage is capped at 3,343 sq ft plus 5% of the area above 21,780 sq ft.
  • Development coverage on such a lot is 5,475 sq ft plus 15% of the area above 21,780 sq ft, counting all buildings and structures, including driveways, parking areas, walks, decks and terraces.
  • Floor area, counting half of garage and basement floors, is capped at 4,792 sq ft on a lot of 21,780 to 24,200 sq ft, rising in steps to 5,770 sq ft at 38,720 sq ft or more.
  • No more than 10% of the minimum lot area may be under water, floodway or wetland.
  • A yard equal to the front yard is required along every lot line that abuts a street, and no accessory building, deck, porch or terrace may stand in a required yard.
  • A multifamily designed residential development needs a Planning Board special permit and a site at least 100 times the one-family lot minimum, at 10% building and 20% development coverage.

One-Family Residence District - A lot lying in both R-1/2A and R-1/4A must meet the most stringent lot area, setbacks and coverage of either (§ 60-330), and R-1/2A is the more restrictive. Where no municipal water main lies within 200 ft of the existing or proposed building, the lot must be at least one acre.

  • On a lot of 21,780 to 43,560 sq ft, building coverage is capped at 3,343 sq ft plus 5% of the area above 21,780 sq ft.
  • Development coverage on such a lot is 5,475 sq ft plus 15% of the area above 21,780 sq ft, counting all buildings and structures, including driveways, parking areas, walks, decks and terraces.
  • Floor area, counting half of garage and basement floors, is capped at 4,792 sq ft on a lot of 21,780 to 24,200 sq ft, rising in steps to 5,770 sq ft at 38,720 sq ft or more.
  • No more than 10% of the minimum lot area may be under water, floodway or wetland.
  • A yard equal to the front yard is required along every lot line that abuts a street, and no accessory building, deck, porch or terrace may stand in a required yard.
  • A multifamily designed residential development needs a Planning Board special permit and a site at least 100 times the one-family lot minimum, at 10% building and 20% development coverage.

One-Family Residence District - Building coverage, development coverage and floor area are capped in square feet on a sliding scale by lot area. On a lot of 43,560 to 87,120 sq ft, buildings may cover 4,432 sq ft plus 3% of the area above 43,560 sq ft.

  • Development coverage on such a lot is 8,742 sq ft plus 10% of the area above 43,560 sq ft, counting all buildings and structures, including driveways, parking areas, walks, decks and terraces.
  • Floor area, counting half of garage and basement floors, is capped at 6,098 sq ft on a lot of 43,560 to 48,400 sq ft, rising in steps to 7,320 sq ft at 77,440 sq ft or more.
  • A lot holding a single-family affordable AFFH unit needs 75% of the lot area, and one holding a two-family affordable AFFH unit needs the one-family lot area.
  • No more than 10% of the minimum lot area may be under water, floodway or wetland.
  • A yard equal to the front yard is required along every lot line that abuts a street, and no accessory building, deck, porch or terrace may stand in a required yard.
  • A multifamily designed residential development needs a Planning Board special permit and a site at least 100 times the one-family lot minimum, at 10% building and 20% development coverage.

One-Family Residence District - A lot lying in both R-1A and R-1/2A must meet the most stringent lot area, setbacks, building coverage and development coverage of either (§ 60-330), and R-1A ranks as the more restrictive, so its figures apply.

  • On a lot of 43,560 to 87,120 sq ft, building coverage is capped at 4,432 sq ft plus 3% of the area above 43,560 sq ft.
  • Development coverage on such a lot is 8,742 sq ft plus 10% of the area above 43,560 sq ft, counting all buildings and structures, including driveways, parking areas, walks, decks and terraces.
  • Floor area, counting half of garage and basement floors, is capped at 6,098 sq ft on a lot of 43,560 to 48,400 sq ft, rising in steps to 7,320 sq ft at 77,440 sq ft or more.
  • No more than 10% of the minimum lot area may be under water, floodway or wetland.
  • A yard equal to the front yard is required along every lot line that abuts a street, and no accessory building, deck, porch or terrace may stand in a required yard.
  • A multifamily designed residential development needs a Planning Board special permit and a site at least 100 times the one-family lot minimum, at 10% building and 20% development coverage.

One-Family Residence District - A lot lying in both R-1A and R-1/4A must meet the most stringent lot area, setbacks, building coverage and development coverage of either (§ 60-330), and R-1A ranks as the more restrictive, so its figures apply.

  • On a lot of 43,560 to 87,120 sq ft, building coverage is capped at 4,432 sq ft plus 3% of the area above 43,560 sq ft.
  • Development coverage on such a lot is 8,742 sq ft plus 10% of the area above 43,560 sq ft, counting all buildings and structures, including driveways, parking areas, walks, decks and terraces.
  • Floor area, counting half of garage and basement floors, is capped at 6,098 sq ft on a lot of 43,560 to 48,400 sq ft, rising in steps to 7,320 sq ft at 77,440 sq ft or more.
  • No more than 10% of the minimum lot area may be under water, floodway or wetland.
  • A yard equal to the front yard is required along every lot line that abuts a street, and no accessory building, deck, porch or terrace may stand in a required yard.
  • A multifamily designed residential development needs a Planning Board special permit and a site at least 100 times the one-family lot minimum, at 10% building and 20% development coverage.

One-Family Residence District - Where there is no municipal water main within 200 feet of the existing or proposed building, the minimum lot reverts to the R-1A requirement of one acre.

  • On a lot of 11,250 to 21,780 sq ft, building coverage is capped at 2,500 sq ft plus 8% of the area above 11,250 sq ft, and at 22% on a smaller lot.
  • Development coverage on such a lot is 4,000 sq ft plus 14% of the area above 11,250 sq ft, and 35% on a smaller lot.
  • Floor area, counting half of garage and basement floors, is capped at 3,158 sq ft on a lot of 10,890 to 12,100 sq ft, rising in steps to 4,100 sq ft at 18,150 sq ft or more.
  • No more than 10% of the minimum lot area may be under water, floodway or wetland.
  • A yard equal to the front yard is required along every lot line that abuts a street, and no accessory building, deck, porch or terrace may stand in a required yard.
  • A multifamily designed residential development needs a Planning Board special permit and a site at least 100 times the one-family lot minimum, at 10% building and 20% development coverage.

Research and Office Business - The front yard may be reduced to 50 ft for a one-story gatehouse or security office, which must still sit at least 150 ft from a residence district.

  • On a development plan the Planning Board may cut that 150 ft to no less than 60 ft for equivalent screening, or where the lot abuts a utility or railroad right-of-way or a limited-access highway.
  • The side and rear yards may be reduced to 100 ft where the lot adjoins a lot in a business or industrial district, and to 50 ft for a one-story gatehouse or security office.
  • Parking and loading areas must be at least 100 ft from the front, side and rear lot lines.
  • A driveway must be at least 100 ft from a side or rear lot line abutting a residence district unless the Planning Board approves less.
  • The bulk and dimensional regulations do not apply to a property on which an existing building is adaptively reused for residential use.
  • A buffer screening strip at least 10 ft wide is required along any lot line abutting a residence district (§ 60-420D(2)).

Designed Business - The front yard rises to 75 ft where off-street parking sits in it. Any side yard that is provided must be at least 6 ft, and at least 75 ft if parking sits in it.

  • Multifamily dwellings follow the standards of the MFR-C district, including its land per dwelling unit density ladder, at 20% building and 35% development coverage.
  • A side yard must be at least 10 ft where it adjoins a street and at least 25 ft where it is used as access to off-street parking.
  • The rear yard must be at least 25 ft where it is used as access to off-street parking and at least 50 ft where the lot adjoins a residence district.
  • No rear yard is required where the lot abuts the side line of a business lot.
  • Parking and loading areas must be at least 15 ft from the lot lines, or less between adjoining business parking areas with Planning Board approval.
  • A buffer screening strip at least 10 ft wide is required along any lot line abutting a residence district (§ 60-420D(2)).

Retail Business - The front yard rises to 75 ft where off-street parking sits in it. No side yard is required where the lot abuts a business lot, but any side yard that is provided must be at least 6 ft.

  • Multifamily dwellings follow the standards of the MFR-C district, including its land per dwelling unit density ladder, at 20% building and 35% development coverage.
  • A side yard must be at least 10 ft where it adjoins a street and at least 25 ft where it is used as access to off-street parking.
  • A building must be at least 2 stories and 30 ft high unless its use is exempt from that rule, and any story above the street level floor must be fitted for later residential use (§ 60-410C).
  • Apartments are allowed above or below the street level floor of a nonresidential building (§ 60-410H(6)).
  • Workforce housing by Town Board special permit, on lots within 1500 ft of the Chappaqua railroad station, uses the B-R lot and bulk figures (§ 60-430O(15)).
  • A buffer screening strip at least 10 ft wide is required along any lot line abutting a residence district (§ 60-420D(2)).

Retail Business and Parking - Buildings must sit within the building areas shown on the adopted B-RP Zoning District Map, and floor area may not exceed 2.0 times the designated building area.

  • By North Greeley Net Zero Carbon special permit a mixed-use building may reach 50 ft and four stories, free of that floor area limit, though the Town Board may set a lower height.
  • That permit needs a lot of at least 33,000 sq ft on the west side of North Greeley Avenue, not a corner lot, with ground floor retail or commercial use.
  • A building must be at least 2 stories and 30 ft high unless its use is exempt from that rule, and any story above the street level floor must be fitted for later residential use (§ 60-410C).
  • No side or rear yard is required where the lot abuts a business lot; one that is provided must be at least 6 ft, 10 ft where it adjoins a street and 25 ft where used for access to off-street parking.
  • Under that permit, land per dwelling unit is at least 375 sq ft for an efficiency, 500 for one bedroom and 750 for two.
  • A buffer screening strip at least 10 ft wide is required along any lot line abutting a residence district (§ 60-420D(2)).

General Industrial - The side yard and the rear yard must each be at least 25 ft along any street.

  • The minimum average lot width is 60 ft.
  • Workforce housing by Town Board special permit, on lots within 500 ft of the Chappaqua railroad station, uses the B-R lot and bulk figures (§ 60-430O(15)).
  • Parking and loading areas need no setback.
  • A buffer screening strip at least 10 ft wide is required along any lot line abutting a residence district (§ 60-420D(2)).

Planned Industrial - The yard from a residence district must be at least 150 ft, which the Planning Board may cut on a development plan to no less than 60 ft for equivalent screening, or where the lot abuts a utility or railroad right-of-way or a limited-access highway.

  • The lot need only be at least 7.5 acres where it abuts a railroad or limited-access highway right-of-way.
  • The 100 ft yard applies to the front, side and rear lot lines alike.
  • Parking and loading areas must be at least 25 ft from the front, side and rear lot lines, and a driveway at least 50 ft from a side or rear lot line abutting a residence district.
  • A buffer screening strip at least 10 ft wide is required along any lot line abutting a residence district (§ 60-420D(2)).

ADUs vs. short-term rentals in New Castle

No local short-term-rental law on record - which is not the same as permission for Town of New Castle. The Town of New Castle has no local short-term rental law, and that is not the same as permission. Confirm with the building department before counting on the use. These are separate questions from whether you can build an ADU — a unit you're allowed to add isn't automatically one you're allowed to rent nightly, so check both.

Good to know

ADU FAQ — New Castle, NY

Are ADUs allowed in New Castle, NY?

Town of New Castle has 17 districts. 9 districts prohibit ADUs, 8 allow them with occupancy restrictions. Check your address with the free ADU checker, or confirm with the building department at (914) 238-4723.

Do I need a special permit for an ADU in New Castle?

No district in Town of New Castle requires a special-use permit for an ADU - 9 districts prohibit ADUs, 8 allow them with occupancy restrictions. Site-plan review or a building permit may still apply.

Can I use an ADU as a short-term rental in New Castle?

No local short-term-rental law on record - which is not the same as permission for Town of New Castle. ADU occupancy and short-term-rental rules are separate: an ADU you can build isn't automatically one you can rent nightly. Confirm both before you count on STR income.

What an ADU costs to build in New Castle

Permission is one question and budget is another. An 800 sq ft accessory unit here runs roughly $235k–310k at a standard finish, and the per-square-foot rate comes in above a full house because the kitchen, bath, panel and heating plant cost the same either way. See the full cost to build an ADU in New Castle, priced by size.

How we know this

Sections analyzed
Ch. 60 § 60-420B(5)(a)-(h) Accessory apartments in one-family residence districts (L.L. No. 6-1981, last amended L.L. No. 1-2019); § 60-210 definition; § 60-300 classes of districts
Districts confirmed
17 of 17 — every mapped district.
Last reviewed
Not covered here
Overlay districts, the zoning map, and any conditions attached to an individual parcel. Size limits and owner-occupancy terms sit in the code section above, not in this summary.

ADU information for Town of New Castle is compiled from the municipal code (last reviewed 2026-09-21) and provided for decision-support only — not legal or architectural advice. ADU eligibility, size, owner-occupancy and permit conditions vary by district and often carry exceptions; verify with the building department at (914) 238-4723 before relying on any answer. Source: the Offsite / Aldo zoning dataset.

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