ADU rules in Stillwater

Stillwater's Land Development Code (City Code Chapter 23) has no accessory dwelling unit use, and a detached second home on a residential lot is not allowed. The only detached accessory living space is a 'detached guest house without kitchen facilities', allowed only in the RS (single-family) districts for occasional guests and expressly not as a rental unit; without a kitchen it is not a dwelling unit. The RSL, RSS and RT districts each allow 'not more than one principal structure' per lot, and the single-family definition requires a lot 'unoccupied by any other dwelling unit or principal structure'. Only the NTZ Neighborhood Transition Zone (a buffer district reached by rezoning) allows multiple principal structures on a lot.

No attached ADU use exists. The lawful route to a second attached unit is a two-family dwelling (duplex), permitted by right in the RT Two-Family Residential district (7,500 sq ft minimum lot, 60 ft width) and in the RTM, RMI and NTZ districts, but not in the RSL or RSS single-family districts that cover most neighborhoods. Stillwater defines two-family as two dwelling units 'placed adjacent to one another with structural parts touching' on a lot with no other principal structure, so an attached unit added to a house in RT is built and permitted as a duplex.

Because the code has no accessory dwelling use, there is no ADU floor-area cap. A two-family dwelling in the RT district is limited by the district's bulk rules: 7,500 square foot minimum lot, 60 foot minimum width, 40 percent maximum lot coverage and a 35 foot height limit, with 20 foot front and rear and 5 foot side setbacks for residential structures. A detached guest house without a kitchen in the RS districts is an accessory structure capped at the principal building's height, with accessory structures covering no more than 20 percent of the required rear yard and 3 foot side and rear setbacks.

Nothing in Chapter 23 requires the owner to live in either half of a duplex, which is the only route to a second dwelling unit. Owner occupancy matters only for short-term rentals: under Ordinance No. 3604 (adopted 6-15-2026), homestead-exempt owner-occupied properties are excepted from the 20 percent per-block short-term rental cap in the RSS and RSL districts. Oklahoma has no state owner-occupancy rule for accessory units.

There are no ADU-specific parking rules. Single-family and two-family dwellings need two off-street spaces per dwelling unit with one or two bedrooms, and one space per bedroom with three or more bedrooms, so adding a duplex unit adds its own parking requirement.

A duplex is a by-right use in the RT, RTM, RMI and NTZ districts, so it needs only a building permit and staff zoning review; there is no ADU permit and no hearing. A guest house without a kitchen is a permitted accessory structure. Putting a second unit on an RSL or RSS lot would require rezoning (a council decision after public notice), which is a legislative act, not an ADU permit.

Stillwater has no long-term rental registration, so either unit of a duplex may be leased. A guest house without a kitchen may house only occasional guests and 'not ... rental units for permanent household occupancy'. Short-term rentals (stays up to 30 consecutive days, including a 'habitable accessory structure') require an annual license; Ordinance No. 3604, adopted 6-15-2026 and not yet codified, replaced the 2019 rules (which limited short-term rentals to RSL, RSS and RT with a neighbor-objection hearing) with a by-right license in all districts issued by Development Services, a cap of 20 percent of dwelling units per block in RSS and RSL (homestead-exempt owner-occupied homes excepted), state sales tax registration and posted house rules. In the Westwood Neighborhood Conservation Overlay, no more than three unrelated persons may occupy a dwelling unit without a special occupancy permit.