ADU rules in Hempstead

A detached backyard cottage is not a permitted use anywhere in the town's residence districts. Each district's use list is closed ("for any of the following purposes and for no other") and allows only a single-family detached dwelling or a senior residence (§ 16 in A, incorporated by reference in AA, A1 and A2; § 63 in B and BB; § 83 in C, which adds two-family; § 177 in the Levittown Planned Residence District). A senior residence is itself a single-family detached dwelling with a second kitchen installed inside it, not a second building. Detached accessory buildings other than a private garage are limited to one structure of no more than 144 square feet of floor area, nine feet high, in the rear yard only (§ 28C, § 75C, § 95C), which forecloses converting a shed or building a cottage; a garage conversion into living space would create a prohibited second dwelling unit. The only route would be a use variance from the Board of Zoning Appeals, which requires proof of unnecessary hardship.

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.

For a senior residence, "at least one of the two separate dwelling areas authorized by a senior residence permit shall not exceed 800 square feet in total floor space" (§ 256E(5)(a), effective 2-21-1994), so the smaller unit is the one that is capped and the owner may occupy either side. The dwelling must also remain "restorable readily to a one-family residence in the judgment of the Department of Buildings" (§ 256E(5)(b)), which limits how far the conversion can go. The Building Zone Ordinance sets no floor-area cap for a mother-daughter or immediate family second unit; the Board of Architectural Review instead judges suitability qualitatively (Town Code § 85-3), and the town's filing instructions require a non-structural plan showing how the house reverts to a single dwelling unit. Ordinary district limits still apply: no dwelling under 1,000 square feet of habitable floor space (§ 299), 2 1/2 stories and 30 feet maximum for a single-family dwelling (§ 21A), and 25% lot coverage in an A Residence District (§ 22).

Both permits are owner-occupancy permits and nothing in New York State law preempts that. A senior residence is defined as "an owner-occupied single-family detached dwelling"; the owner must be a natural person and must swear that he or she "presently and permanently is residing at the premises" (§ 256E(1)(d)), and the permit terminates if the Department of Buildings finds the owner (or the coresident spouse whose age qualifies the property) has not resided there for 90 or more days in any two-year permit period (§ 256E(3)(c)). A mother-daughter residence turns on a "fee resident owner"; the status "shall immediately terminate" if no fee resident owner and approved qualifying relative are permanent residents, with "permanent resident" defined as actually residing at the premises more than 186 days per year, excepting active federal military duty (§ 267D(2)(d)[4]). In both cases the second kitchen and separate entrance must come out when the permit lapses.

The Building Zone Ordinance's off-street parking schedule (§ 319A) applies to multiple-family dwellings of three or more units, hotels, places of assembly and non-residential uses; single-family detached dwellings are not on the list, and neither a senior residence nor a mother-daughter residence carries an added space requirement. Parking is still reviewed rather than ignored: "off-street parking" is one of the factors the Board of Architectural Review weighs when deciding whether a house is acceptable for mother-daughter use (Town Code § 85-3D), and the town's filing instructions require a plot plan showing parking for every car listed on the supplementary statement. A rental occupancy permit application must likewise show "the number, location and access of existing and proposed onsite vehicle parking facilities" (Town Code § 99-14A(9)). Expect the practical expectation to be enough driveway for both households.

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)).

The senior residence rules expressly contemplate a tenant: the ordinance repeatedly refers to the "second-family lessee", who must file an affidavit consenting to inspection and acknowledging that "upon the lapse of the senior residence permit the lessee shall be required to vacate the premises" (§ 256E(5)(c)), and no family relationship to the owner is required. A mother-daughter or immediate family unit is the opposite: the second kitchen is "for the sole use by the children or parents of the fee resident owner" (or a sibling), and the Board of Zoning Appeals grant "shall be terminated upon" the "sale or lease of the mother-daughter premises" (§ 267D(2)(d)[3][a]). Any other rented dwelling unit in the town needs a rental occupancy permit under Town Code Ch. 99 Art. II ($500, two-year term, on-site inspection, advertising an unpermitted rental is itself an offense under § 99-25), though units under a senior residence or mother-daughter permit are exempt from that permit (§ 99-31A, B). Short-term rental is prohibited outright: "No rental occupancy permit shall be granted to a transient rental property, and no person shall use or permit the use of a property or portion thereof as a transient rental property" (§ 99-13D, effective 7-10-2023), with "transient rental property" defined as occupancy for less than 28 nights and an Airbnb, HomeAway or VRBO listing creating a rebuttable presumption. The second unit cannot be sold separately; it is part of a one-family dwelling that must stay readily restorable.