Compare ADU rules across New York

An attached or internal second unit is treated very differently from a detached guest cottage and is the harder path under APA rules. A 'single family dwelling' is 'any detached building containing one dwelling unit' (Executive Law section 802(58)), so putting a second dwelling unit inside the house takes the building out of that category: 9 NYCRR 570.3(x) defines a multiple family dwelling to include 'the conversion of an existing single family dwelling' designed for occupancy in separate dwelling units by more than one family. Multiple family dwellings are class B regional projects requiring an Agency permit in Moderate Intensity Use, Low Intensity Use and Rural Use areas (Executive Law section 810(2)(a)(3), (b)(3), (c)(3)), and they appear on neither the primary nor the secondary compatible use list for Resource Management or Industrial Use areas, so the Agency's chart shows them there as an incompatible use requiring a class B permit plus a demonstration of compatibility. Only in Hamlet areas is a converted two-unit building non-jurisdictional, and even there 100 or more residential units becomes a class A project. A basement, attic or addition conversion is therefore possible but generally requires APA review outside Hamlet areas, on top of town zoning.

Ordinance read August 2026

An internal accessory apartment inside an existing one-family house is allowed, but only with a special permit granted case by case by the nine-member Accessory Apartment Review Board after a noticed public hearing, not as of right. Section 153-14 gives the Board the power to hear "all accessory apartment permit applications" and to "impose such conditions and safeguards as it may deem appropriate," and section 153-16A requires a public hearing for every new application. The unit must be inside the main dwelling and no part of it may be in the cellar (section 153-18D); zoning section 213-250.4, added 8-7-2024 by L.L. No. 15-2024, separately bans kitchens in basements and states that "accessory apartments shall be prohibited in basements" in the AA, A, B, C and D Residence districts, which closes off the most common conversion. Section 153-18H also bars any application for three years after a certificate of occupancy is issued for the dwelling. Practically, an attic, second-floor or first-floor conversion is the path that remains.

Ordinance read August 2026

This is a discretionary special permit, not an over-the-counter approval. Section 153-14 vests the nine-member Accessory Apartment Review Board with the power to "make a final determination as to whether the applicant should be granted any such permit" after finding that the use will not impair neighboring properties and will be in harmony with the article, and it may attach conditions. Section 153-16A requires a public hearing on every new application, with newspaper notice at least five days out, and section 153-17 requires the applicant to post 30-inch by 40-inch blue-on-white signs on the property for at least 10 days beforehand. Renewals skip the hearing if there have been no code violations or neighbor complaints during the permit term (section 153-16B). Building Division review, a floor plan, a survey and an inspection (or a licensed engineer's or architect's certification) come on top, and the only appeal from the Board is an Article 78 proceeding in State Supreme Court (section 153-26).

Ordinance read August 2026

An accessory apartment carved out of the principal one-family dwelling (basement, attic, wing or internal conversion) is allowed, but as a licensed accessory use with real gates rather than an as-of-right unit. Section 85-258A authorizes accessory apartments in the A Residence, A Residence 1, A Residence 2, A Residence 5, B Residence, B Residence 1 and C Residence Districts, and § 85-190B(8) lists them as an accessory use in the A Residence District (the other residence districts adopt that accessory-use list by cross reference). The conditions that most often bite: the owner must live in the same dwelling, only one accessory apartment is allowed per lot and per dwelling and per homeowner, the unit may have only one bedroom, entities such as LLCs and corporations cannot hold a license, an accessory apartment is barred in an existing multifamily structure, and no license may issue where 5% or more of the lots within a half-mile radius already have accessory apartments.

Ordinance read August 2026

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.

Ordinance read August 2026

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.

Ordinance read August 2026

An internal second unit is allowed only through one of two narrow permits, both tied to who will live in it. A senior residence (§ 256E) lets the Department of Buildings issue a building permit for a second kitchen and/or separate entrance inside an owner-occupied single-family detached dwelling, but only if the owner or the owner's coresident spouse is at least 62 years old. A mother-daughter residence (§ 272A(10) and § 272B(13)) is a second kitchen for the sole use of the children or parents of the fee resident owner, and an immediate family residence is the same arrangement for a sibling; both need a Board of Zoning Appeals special exception after a public hearing and a Board of Architectural Review recommendation. Outside those two permits, a second kitchen or a lockable separate living space in a one-family dwelling is an illegal two-family occupancy: § 255.1 sets rebuttable presumptions from extra meters, extra entrances, extra mailboxes or doorbells, and a lease.

Ordinance read August 2026

It depends entirely on which second-unit path you qualify for. A senior residence is administrative: "the Department of Buildings shall issue a building permit for such use or for installation of a second kitchen and/or separate entrance authorized thereby" once the age affidavits, the owner-residence affidavit, the recorded declaration of restrictive covenants and a clean-violations inspection are in hand (§ 256E(1)); the permit runs two years and renews on updated affidavits, at a $150 application or renewal fee. A mother-daughter or immediate family residence is discretionary: it is a special permit use under § 272A(10) and § 272B(13), so the Board of Zoning Appeals must hold a public hearing and make the § 267D(2)(a) and (b) findings, and the application cannot even be heard until the Board of Architectural Review has reviewed it (Town Code § 85-11). The Board may make its grant temporary and renewable (§ 267D(3)).

Ordinance read August 2026

An ADU inside the existing single-family house is allowed, but only as a conditional use granted by the Zoning Board of Appeals after a noticed public hearing, and only if a long list of gates is cleared: the house must be the owner's principal residence, the lot must be at least 5,000 sq ft with 50 feet of frontage, the dwelling must have held a single-family certificate of occupancy for at least three years, and fewer than 10 percent of the lots within a half-mile radius may already contain ADUs. Only one ADU is allowed per dwelling and per lot, and a homeowner gets only one permit. Since L.L. No. 34-2019 took effect on July 16, 2019 a basement or cellar can no longer be used as an ADU unless a permit was already in effect (or an application was already on file) by that date, and the Town's Accessory Dwelling Unit Bureau states it no longer accepts basement, cellar or attic applications. No new front entrance may be created, other new exterior doors must go on the sides or rear, and no exterior change may alter the building's single-family appearance.

Ordinance read August 2026

This is a discretionary special-use permit, not a ministerial sign-off. Section 198-133(A)(1) makes an ADU a conditional use 'only by permission of the Zoning Board of Appeals,' and § 198-134(A) bars issuance until after a public hearing under § 198-137. The Town publishes notice in the official newspaper once a week for two consecutive weeks, and the applicant must mail notice to every property owner within 500 feet at least 20 days before the hearing and file certificates of mailing. A Hearing Officer takes testimony and files written findings with the ZBA within 62 days; the ZBA makes the final determination and may attach conditions. Before granting, the Board must affirmatively find the unit will not add traffic congestion, will not significantly hurt neighboring property values, and will not unreasonably conflict with a stable, uncongested single-family environment. A denial blocks a new application by the same owner for one year and a revocation blocks reapplication for three years. Renewals and transfers normally proceed without a hearing unless the Hearing Officer calls one.

Ordinance read August 2026

An attached or internal accessory apartment (a basement, attic or interior conversion, or an addition that keeps the unit inside the principal structure) is the only form Islip allows, and it needs a discretionary accessory apartment permit from the Zoning Board of Appeals plus a certificate of occupancy from the Department of Building (§ 68-602). Several gates commonly bite: the lot must be at least 7,500 square feet (§ 68-606) and at least 75 feet wide (§ 68-607); a dwelling whose certificate of occupancy postdates September 1, 1992 must be at least seven years old (§ 68-613); and the house must already hold a certificate of occupancy or compliance as a single-family dwelling, with only one accessory apartment per lot (§ 68-609). Exterior changes may not alter the single-family appearance of the house, only one visible front entrance is allowed (a second front door is permitted only if the Board finds it existed on or before July 7, 1992 under a two-family, family-use-only permit), and meters serving the apartment must not be visible from any roadway (§ 68-610B). Before occupancy the unit has to meet all New York State Uniform Fire Prevention and Building Code requirements for two-family dwellings, within six months of the building and zoning permit (§ 68-604).

Ordinance read August 2026

Approval is discretionary, not ministerial. § 68-602 requires an accessory apartment permit from the Zoning Board of Appeals plus a certificate of occupancy for the use from the Department of Building, and § 68-615D requires "a public hearing before the Town of Islip Zoning Board of Appeals ... for all applications for an accessory apartment permit, except for renewals by the same owner and transfers of said permit." The applicant must file a notarized acknowledgment that the use and permit end on death, transfer of title, the owner moving out, or conviction for a violation, and the grant lapses if a building and change-of-use permit is not obtained within 90 days (§ 68-615B, E). The code and the Town's forms treat it as a temporary special permit; any variance needed alongside it is heard by the same Board under § 68-621.2. The ZBA fee schedule effective May 1, 2024 charges $350 for a new accessory apartment application and $200 for the three-year renewal.

Ordinance read August 2026

No owner-occupancy standard for accessory units can exist because New Rochelle authorizes no accessory units; the code is simply silent. Owner occupancy does appear in two adjacent places, which is why the answer is 'not addressed' rather than 'no'. Renting a single non-housekeeping room to at most two people is a permitted accessory use 'for owner-occupied dwellings only' in every residence district (§ 331-30B(2) and parallels), and a bed-and-breakfast is defined in § 331-4 as renting not more than three rooms 'in an owner-occupied dwelling' to not more than six transient roomers. Renting out an entire lawful one-family or two-family dwelling carries no owner-occupancy condition. New York has no statewide ADU statute that would preempt a local owner-occupancy rule in either direction.

Ordinance read August 2026

There is no ADU permit pathway of any kind: no district lists an accessory dwelling as a permitted, accessory or special-permit use, and § 331-29A states that any use not specifically listed as permitted is deemed prohibited. The only route to a second unit on a one-family lot is a use variance from the Board of Appeals on Zoning under § 331-133F, which requires the applicant to prove unnecessary hardship for each and every permitted use in the district: no reasonable return shown by competent financial evidence, a hardship unique to the property, no alteration of the essential character of the neighborhood, and a hardship that is not self-created. That is a demanding discretionary standard, not an administrative approval. Where two-family dwellings are already permitted (R2-7.0 and the RMF districts), converting to a two-family is a by-right building permit matter subject to the district's dimensional standards and § 331-137 certificate of occupancy rules, not an ADU process.

Ordinance read August 2026

Detached backyard ADUs are allowed on single- and two-family zoning lots in every borough, but four carve-outs written into the December 5, 2024 definition knock out large areas. New 'backyard ancillary dwelling units' are barred in R1-2A, R2A and R3A districts beyond the Greater Transit Zone, in every Landmarks Preservation Commission historic district, and inside the DEP-mapped 10-year rainfall flood risk area and coastal flood risk area (DEP's Interim Flood Risk Area Map rule took effect September 23, 2025). Special Coastal Risk Districts allow no ADU at all, and the Special Bay Ridge District bans backyard ADUs west of Ridge Boulevard and south of Marine Avenue. A backyard ADU must also be reachable directly from a side yard or open area at least five feet wide, which rules out most attached row houses. Converting or rebuilding a detached structure that existed before December 5, 2024, such as a garage or shed, is still permitted where new backyard ADUs are banned, though it cannot be used to legalize a structure that was already non-complying in a required yard or open space.

Ordinance read August 2026

There is no ADU category, but a second unit created inside or attached to an existing house is a 'dwelling unit conversion' and is allowed where two-family dwellings are a permitted use: the R-2 Medium-Density (§120-17C) and R-3 High-Density (§120-26C) Residential Districts. It is flatly barred in R-1 Low-Density, where §120-8 permits only single-family dwellings and §120-10 prohibits any conversion that increases the number of residential units. Even in R-2 and R-3 the conversion must clear all of §120-166: a lot of at least 6,000 sq ft, a building with at least 1,500 sq ft of habitable floor area, a minimum size for the new unit, and full off-street parking compliance. The definition of 'dwelling unit conversion' covers additions and enlargements, not just interior remodeling, so a bump-out addition holding the second unit is judged by the same standards.

Ordinance read August 2026

There is no ADU permit, so the path depends on the district and on whether the conversion standards are met. In R-2 or R-3, a conversion that satisfies every §120-166 standard is administrative: the Director of Zoning and Permitting issues a certificate of zoning compliance under §120-189 (required for any change in use or occupancy and for work needing a building permit), then the work needs a building permit and a fresh certificate of occupancy. A conversion that misses any §120-166 standard goes to the Zoning Board of Appeals on an unnecessary-hardship or area-variance showing under §120-195, which is a noticed discretionary hearing. In R-1, or for any detached unit anywhere, the only route is a use variance. Properties in a Preservation District or designated as Buildings of Historic Value also need a certificate of appropriateness from the Preservation Board.

Ordinance read August 2026

Table 3.1 lists "Accessory dwelling unit, Detached" as an allowed accessory use (A) in R1, R2, R3, R4 and R5 and in MX-1, MX-2 and MX-3, and gives it no designation at all in MX-4, MX-5, CM, LI or OS. The condition that bites is § 3.4D(1)a.ii: an ADU is allowed only on a lot with an owner-occupied Single-Unit Detached dwelling in the Residential Living Use Category, so two-unit houses, rowhouse-style single-unit attached dwellings and landlord-owned rentals are shut out entirely. Only one ADU is allowed per property or lot of record whether attached or detached, a detached unit must sit to the side or rear of the house, and no ADU may sit forward of the front façade of the primary dwelling. Within those limits the approval itself is administrative: Minor Site Plan Review decided by the Zoning Administrator, no hearing.

Ordinance read August 2026

"Accessory Dwelling Unit, Attached" carries the same A designation in R1 through R5 and MX-1 through MX-3, and is subject to the same eligibility gate: only on a lot with an owner-occupied single-unit detached house. § 3.4D(1)b.i defines attached as at least 25 percent of the ADU's total wall area, or its floor or ceiling, fully connected to a wall, floor or ceiling of the principal residential structure, which covers basement, attic, addition and internal conversions. Because only one ADU is allowed per lot, an internal unit and a backyard cottage cannot coexist. Every ADU must have a separate exterior entrance and contain cooking, sleeping and sanitary facilities, may have only one kitchen (partial or full), and any outside access stairway must be off the street-facing façade.

Ordinance read August 2026

There is no accessory or internal ADU, but a second unit inside the building is possible where 'Two family dwelling' is a Permitted Principal Use: R2-4, R2-2.5, RM-2.5, RM-1.5, RM-1.5T, RM-1, RM-0.7 and RM-0.35. All five one-family districts (R1-30, R1-20, R1-12.5, R1-7.5 and R1-5) permit only a one-family dwelling, so a basement or internal conversion there is prohibited outright. Where two-family is allowed the conversion is gated by minimum lot area per dwelling unit (4,000 sq ft per unit in R2-4, 2,500 in R2-2.5 and RM-2.5, 1,500 in RM-1.5 and RM-1.5T, 1,000 in RM-1, 700 in RM-0.7, 350 in RM-0.35) and by 2 off-street parking spaces per unit. Note the legal form: a two family dwelling is defined as a dwelling containing two principal dwelling units, so neither unit is accessory to the other and neither is subject to ADU-style size or occupancy limits.

Ordinance read August 2026

The review depends entirely on which path a homeowner takes. A two-family dwelling in R2-4, R2-2.5 or an RM district is a Permitted Principal Use, and Section 7.1.1 exempts one-family and two-family dwellings (on parcels with no environmentally sensitive feature) from site plan approval, so the conversion is ministerial: a building permit and certificate of use and occupancy from the Department of Building. An accessory servants quarters in R1-30, R1-20, R1-12.5 or R1-7.5 needs a special permit, and because the use appears in neither the Common Council list (Section 6.2.1) nor the Planning Board list (Section 6.2.2) the approving agency defaults to the Board of Appeals, which must hold a noticed public hearing within 45 days and apply the general standards of Section 6.5. In every other case, including any second unit in R1-5 or a detached second dwelling, the use is prohibited and would require a use variance from the Board of Appeals under Section 10.3.5.1.

Ordinance read August 2026

None of permitted, conditional-use or varies describes Yonkers, because there is no approval pathway for a new ADU at all. Table 43-1 lists accessory apartments neither as a permitted accessory use (P or Ps) nor as a special use (S) in any district, and § 43-27 prohibits unlisted uses, so a special use permit under Article VII is not available. The only administrative permit that touches accessory apartments is the § 43-22B(1)(a) certificate of occupancy application to the Commissioner of the Department of Housing and Buildings for a preexisting unit, made on department forms with the Standard Accessory Apartment Affidavit and an interior inspection; that is a legacy legalization and transfer process, not a way to create a unit. Anything new needs a discretionary use variance from the Zoning Board of Appeals under § 43-85, which demands proof that no permitted use yields a reasonable return, that the hardship is unique and not self-created, and that neighborhood character is preserved.

Ordinance read August 2026