ADU rules in Auburn

A detached backyard ADU is a permitted use on a single-family lot across Auburn's residential and mixed-use districts. The table in section 60-53 lists 'Permitted' in the Low Density Country Residence, Low Density Rural Residence, Suburban Residence, Urban Residence, Multifamily Suburban, General Business, General Business II and downtown Form Based Code districts, and section 60-34(2) exempts 'the addition of an accessory dwelling unit' from the one-principal-building-per-lot rule wherever two-family dwellings are allowed. The lot areas the table shows for 'the first unit with accessory dwelling unit' are simply each district's ordinary minimum lot size (10,000 square feet in Urban Residence, 21,780 in Suburban Residence, one acre in Low Density Rural Residence, three acres in Low Density Country Residence), so the ADU itself requires no extra land. Two areas are different: the Lake Auburn Watershed Overlay District, which 30-A M.R.S. section 4364-B(1-B) removes from the state ADU mandate and where section 60-952(a)(1) prohibits new dwelling units over the agriculture zone, and the Industrial district, where an ADU is allowed only for legally existing dwellings built before January 1, 2024.

Auburn treats internal, attached and detached units identically. Section 60-2 defines an accessory dwelling unit as one 'located within, attached to or detached from a single-family dwelling unit located on the same parcel of land,' and the section 60-53 table has a single 'Accessory Dwelling Unit' column that does not distinguish the three forms, so a basement or internal conversion and a wall-sharing addition are permitted wherever a backyard cottage is. Chapter 60 adds no separate entrance, design or utility-separation conditions for the attached form. Related but distinct paths exist alongside it: section 60-35 lets a one-family house built before January 1, 1958 convert to a two-family, and in the comprehensive plan's designated growth area section 60-34(4) lets a lot with an existing dwelling add one attached unit, one detached unit, or one of each for three units total.

Section 60-2 defines an accessory dwelling unit as 'a self-contained dwelling unit meeting a minimum of 190 square feet and not to exceed 1,500 square feet.' There is no percentage-of-primary-dwelling cap and no ADU-specific height rule, so the district height limit governs: 2½ stories or 35 feet in the Agriculture and Resource Protection, Low Density Country Residence, Low Density Rural Residence, Suburban Residence and Urban Residence districts. The 190 square foot floor mirrors 30-A M.R.S. section 4364-B(6) and yields to any different minimum the Technical Building Codes and Standards Board adopts under 10 M.R.S.A. section 9722. Setbacks are the district's normal building setbacks; section 60-53 states that setback standards 'shall not be reduced to allow for additional dwelling units and shall not be increased for subsequent dwelling units.'

Nothing in Auburn's code conditions an ADU on the owner living on the property. A full-text search of the Code of Ordinances returns no owner-occupancy or primary-residence requirement touching dwellings; the only 'owner occupied' references are solid-waste collection fees in section 44-22 and vacant-building fees in section 12-280. Sections 60-53 and 60-34, the two provisions that authorize ADUs, are silent on who occupies either unit, so an investor-owner may build the ADU and rent both units. The state-law backstop is not yet operative: 30-A M.R.S. section 4364-B(4)(E), which bars municipal owner-residence requirements, was enacted by P.L. 2025, ch. 385, section 17, and P.L. 2025, ch. 733, section 25 (signed April 16, 2026, applied retroactively to September 24, 2025) deleted the July 1, 2026 branch of that Act's application clause so that it now reaches all municipalities only from July 1, 2027. Today the answer therefore rests on Auburn's own silence rather than on preemption, which is the more durable ground anyway.

Section 60-608 requires one off-street parking space per dwelling unit for single-family, two-family and multifamily uses and contains no ADU exemption, so the local table read alone would add a space for the ADU. That requirement is preempted: 30-A M.R.S. section 4364-B(4)(C) has provided since Auburn's January 1, 2024 implementation date that an ADU 'may not be subject to any additional parking requirements beyond the parking requirements of the single-family dwelling unit on the lot,' and Auburn's own section 60-952(a)(1) confirms the LD 2003 provisions apply everywhere except the Lake Auburn Watershed Overlay District. Inside that overlay the carve-out at section 4364-B(1-B) switches the state rule off, so section 60-608's one space per unit governs there. Auburn separately rewrote Article V on April 21, 2026 (Ordinance 06-04062026) to track the new parking-minimum statute at 30-A M.R.S. section 4364-F: the one-space-per-dwelling-unit figure stayed, the on-site parking requirement in section 60-607(5) was repealed, and off-site parking agreements within a quarter mile are now allowed in any residential or commercial district. Because the code and the statute point in different directions, confirm the space count with the code office before drawing a site plan.

An ADU is a permitted use rather than a special exception, so it is an over-the-counter approval. Section 60-1401 requires only a building permit from the building inspector, who must find that the plans and intended use satisfy Chapter 60, and section 60-1402 requires a scaled plot plan with the application; applications are filed through the city's SmartGov permit portal. Planning board site plan review under section 60-1278 is triggered only by uses permitted by special exception, so the board is not involved in an ADU. The one wrinkle is the Agriculture and Resource Protection district, where section 60-53 permits an ADU only if the unit meets the district's requirements for a single-family home, which means the planning and permitting director must first approve a farm, agricultural, recreational or natural resource business or land use plan under section 60-145(a)(1)b.2 before a building permit can issue.

Auburn has no short-term rental ordinance, registry or licensing program: a full-text search of the Code of Ordinances turns up no short-term rental, vacation rental or rental-registration provisions, and Chapter 14 licenses no lodging houses. Renting the ADU by the month or the year is unrestricted, with no owner-occupancy condition, no cap on rented units and no primary-residence test. Short stays are handled through a definition instead: section 60-2 provides that 'Dwelling units available for rental or occupancy for periods of less than one week shall be considered boarding/lodging units,' and boardinghouses and lodginghouses are a special exception use requiring planning board approval in the residential districts under section 60-229(b)(2), which the Suburban Residence district adopts by reference in section 60-255(b)(1) and the Urban Residence district adopts in turn in section 60-277(b). A one-week-or-longer rental therefore stays in the dwelling-unit category, while nightly or weekend letting is not permitted by right in Auburn's residential neighborhoods. The ADU sits on the same lot as the house and the code provides no mechanism to sell it separately.