ADU rules in Augusta

Augusta allows one accessory dwelling unit, detached or attached, on any lot that already has a residential use, and since Ord. No. 26-124 (adopted 8-20-2026) that includes lots with apartment buildings and mixed-use buildings, not only one- and two-family homes. The amended Land Use Ordinance § 300-524E reads: 'One Accessory Dwelling Unit shall be allowed on all parcels where a residential use is on the lot.' The same ordinance added one new exclusion: an ADU is 'Not permitted on a lot or portion of a lot within the 100 year flood zone' (§ 300-524E(2)(g)), so a lot even partly inside the mapped floodplain cannot have one (see the first caveat on state law). The Table of Land Uses lists 'Accessory Dwelling Unit' as a permitted use requiring a Code Enforcement Officer permit in every base district except Government Services (GS). A detached ADU only has to meet the accessory-structure setback, five feet from side and rear lines in the RA, RB1 and RB2 residential districts, and density, lot size and on-site parking standards expressly do not apply to it.

The same section covers ADUs inside, attached to, or detached from the existing home. Ord. No. 26-124 (8-20-2026) struck 'one-family' from the § 300-202 definition, which now reads 'a self-contained dwelling unit located within, attached to, or detached from a dwelling located on the same parcel of land,' with self-contained meaning the unit has its own living, cooking and bathroom facilities. A basement, upstairs or internal conversion therefore qualifies, including inside a two-family or multifamily building. § 300-524E(2)(c) requires a 'building addition ADU, attached to the principal structure' to meet the setbacks of the primary structure rather than the looser accessory-structure setbacks. Attached and internal ADUs get the same exemptions from density, lot size and on-site parking as detached ones, and the same 100-year flood zone exclusion applies.

§ 300-524E(2) sets a floor and a proportional ceiling rather than a flat number: 'Minimum floor area shall be at least 190 square feet,' matching the state minimum in 30-A M.R.S. § 4364-B(6), and 'Maximum floor area shall not exceed the floor area of the primary structure on the property.' Ord. No. 26-124 (8-20-2026) left both numbers unchanged. On a large house that is a generous cap; on a small cottage it is the binding constraint. 'Floor area' is defined in § 300-202 as the sum of the horizontal floor areas enclosed by exterior walls plus unenclosed porches and decks. There is no ADU-specific height limit or lot coverage rule; a detached ADU takes the accessory-structure setback (five feet side and rear in RA, RB1 and RB2) and an attached one takes the principal-structure setback (ten feet side and rear in those districts).

Augusta imposes no owner-occupancy requirement. § 300-524E(2) is an exhaustive list of the standards that apply to an ADU (minimum and maximum floor area, setbacks, water and sewer, other applicable codes and, since Ord. No. 26-124, the flood zone exclusion) and contains no residency condition; an eCode360 phrase search for 'owner-occupied' finds only the definition of a tourist home. Maine has enacted an explicit ban on local owner-occupancy rules at 30-A M.R.S. § 4364-B(4)(E), but under PL 2025, c. 733, §§ 25 and 26 it applies to municipalities beginning July 1, 2027. Augusta already satisfies it.

§ 300-524E(1) states that on-site parking standards 'SHALL NOT apply' to an ADU, and the citywide parking schedule in § 300-513 (Table 300-513A, Schedule of Required Off-Street Parking) lists 'Accessory dwelling unit (ADU): None required' under its Residential heading, in contrast to 'Dwelling: 1 per dwelling unit.' The primary house keeps its own requirement; the ADU adds nothing. In the downtown KBD1 district the separate Table 300-513-B applies, and it requires no parking for residential use when an existing building's use is changed or expanded. This matches 30-A M.R.S. § 4364-B(4)(C), which bars parking requirements for an ADU beyond those of the single-family dwelling on the lot. Ord. No. 26-124 did not change any parking text.

An ADU is a by-right, administratively permitted use. The key to the Table of Land Uses reads 'X = Permitted Use (requires a permit from the Code Enforcement Officer)' and distinguishes CU (conditional use, Planning Board review and a public hearing), PB and SE; 'Accessory Dwelling Unit' carries a plain X in every base district except GS. The applicant files a residential building permit with the Bureau of Code Enforcement, either through the city's new online permit portal or on the Residential Building Permit Application form, and the Bureau handles zoning, setback, plumbing and septic sign-off. Two overlays can escalate this. Inside a locally designated historic district, § 300-316.5I(3) requires a historic preservation certificate from the Augusta Historic Preservation Commission for new construction of a principal or accessory structure visible from the street. Inside the Shoreland Overlay an ADU is reviewed as a 'structure accessory to allowed uses,' a Code Enforcement Officer permit in the Limited Residential, General Development and Limited Commercial Districts but a Planning Board permit in the Resource Protection and Stream Protection Districts.

Chapter 300 places no limit on renting an ADU: § 300-524E imposes no occupancy, tenure or family-relationship condition, and § 300-202 defines a dwelling unit to include 'rental units that contain cooking, sleeping, and toilet facilities regardless of the time period rented.' eCode360 phrase searches for 'short-term rental', 'short-term rentals' and 'short term rental' return zero hits across the code and the New Laws bank, and there is no rental registration or lodging license: Chapter 221 (Rental Property) covers only bedbug abatement, and the license list in Chapter 190 has no lodging or short-term rental category. Nightly renting can still trip a zoning use test if it grows into a business: a bed-and-breakfast/tourist home is a separate use needing conditional-use approval in the residential districts, and 'hotel' is defined as more than 16 rooms of transient lodging. The ordinance says nothing about selling an ADU separately from the house; carving off a lot would go through Part 4, Subdivision and Site Plan Review.