ADU rules in Adirondack Park

The Adirondack Park Agency's ADU analog is the 'guest cottage', and the APA overlay allows one park-wide with no Agency permit. Executive Law section 802(5) defines an accessory structure to include 'a guest cottage not for rent or hire that is incidental and subordinate to and associated with a single family dwelling', and 9 NYCRR 570.3(l) sets the operative test: not more than one residential structure per single family dwelling, used only occasionally, used only by guests of the residents, never rented separately, and no larger than half the main house or 2,000 square feet. Accessory uses and structures are a listed primary compatible use in every one of the six land use areas (Hamlet, Moderate Intensity Use, Low Intensity Use, Rural Use, Resource Management, Industrial Use) under Executive Law section 805(3), and the Agency's Jurisdictional Chart marks them non-jurisdictional in all six. A detached second dwelling that does not fit inside the guest cottage box is instead a second single family dwelling: it counts as a principal building against the overall intensity guidelines and needs a class B Agency permit in Resource Management areas. Town and village zoning applies on top of all of this and is usually the binding constraint.

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.

2,000 square feet is the absolute ceiling and the 50 percent test is usually the real cap: 9 NYCRR 570.3(l)(4) requires the guest cottage to contain 'one-half or less of the enclosed floor space of the associated single family dwelling or 2,000 square feet, whichever is less'. A 2,400 square foot house therefore supports a 1,200 square foot guest cottage, not 2,000, and a 4,000 square foot house is the smallest that unlocks the full 2,000. The Agency measures floor space from the structure's exterior walls and counts the sum of all floor areas plus all porches, covered decks and other roofed or covered components, and finished attics and basements, so a covered porch or a finished basement eats into the allowance. Separately, any structure over 40 feet in height is a class A regional project park-wide, guest cottage or not. Exceeding the size test does not forbid the building; it reclassifies it as a second single family dwelling and a principal building.

Neither the APA Act nor the Agency's regulations impose an owner-occupancy requirement. What they impose instead is an occupancy-linkage requirement: 9 NYCRR 570.3(l) allows the guest cottage only where it 'is used only by guests of the resident(s) of the single family dwelling', so the main house has to be occupied and the cottage used by those residents' guests, whether or not the occupant happens to be the owner. Ownership matters at conveyance rather than at occupancy: Agency guidance states that upon conveyance of a guest cottage separately from the associated single family dwelling it 'will no longer be considered accessory' and may become a single family dwelling subject to the overall intensity guidelines. Many Adirondack towns do attach owner-occupancy conditions to accessory apartments in their own zoning, so treat the local code as the place this requirement is most likely to appear.

The APA overlay contains no off-street parking standard for guest cottages or for residential accessory structures generally. The only parking requirement anywhere in the Agency's regulations is 9 NYCRR 573.8(b)(7), which requires one off-street space per room for rent as a condition of treating a bed and breakfast as an accessory use rather than a tourist accommodation, and the same subdivision expressly bars accessory structures and guest cottages from being used as bed and breakfasts. Parking for a guest cottage is therefore purely a question of town or village zoning, subject to the Agency's shoreline and wetland setbacks, which can constrain where a driveway or parking area may be graded.

A conforming guest cottage requires no Adirondack Park Agency permit anywhere in the Park. Under 9 NYCRR 573.1 an Agency permit is needed only for a class A regional project or a class B regional project, and the Agency's Jurisdictional Chart marks 'Accessory Uses/Structures' NJ (non-jurisdictional, no APA permit required) in all six land use areas, including Resource Management, where a second single family dwelling would need a class B permit. Avoiding that review, and the overall intensity guidelines that come with principal building status, is the entire point of the guest cottage classification. Review is still triggered if the structure exceeds 40 feet in height, involves wetlands, sits in a critical environmental area (2,500 feet or higher, within one-eighth mile of wilderness, primitive or canoe areas, or within 150 feet in Rural Use or 300 feet in Resource Management of a state or federal highway right of way), lies within a designated wild, scenic or recreational river corridor, or where a prior Agency permit on the property requires further review. Owners can file a free Jurisdictional Inquiry Form for a binding written determination. A town building permit under the NYS Uniform Fire Prevention and Building Code and town zoning approval are separate and always apply.

This is where the guest cottage stops behaving like a conventional ADU: it cannot be rented out on its own, long term or short term. 9 NYCRR 570.3(l) requires that the cottage 'is not for rent or hire separately from the single family dwelling', that it 'is used only on an occasional basis' and that it be used 'only by guests of the resident(s)', and Executive Law section 802(5) reaches the same result by describing 'a guest cottage not for rent or hire'. Renting it separately forfeits accessory status, at which point the structure becomes a second principal building subject to the overall intensity guidelines and, in Resource Management areas, a class B permit. Renting the whole property is a different matter: Agency guidance updated September 27, 2024 states that a short-term rental is not a jurisdictional tourist accommodation where only one party rents on the lot at a time with no other persons living or renting there, only lawfully existing structures are rented, and no off-site services such as catering or event music are advertised. Guest cottages may not be used as bed and breakfasts (9 NYCRR 573.8(b)(5)). Town short-term rental laws layer on top and several Park towns license or restrict STRs.