Town Permit Guide

Home › Maine › Bath › Accessory Dwelling Units (ADUs)

Can I build an ADU in Bath, Maine?

Bath, Sagadahoc County · Ordinances checked 2026-10-19 · Reviewed · 13 cited sections

Allowed with a permit

Yes. Under Bath's new Land Use Code (in effect since September 23, 2026), you can add one ADU to a lot with a single-family, two-family or multi-family home, inside the house, as an addition, or as a detached building, with a permit from the Codes Enforcement Officer. It can be no larger than 800 square feet or 80% of the main unit, whichever is less, and no parking is required.

ApprovalPermit from the Codes Enforcement Officer [1]
Districts (Table 8-1)R-R, R-T, R-C, R-UC, R-WM, R-WH, NC, CC, DB, CG, MC, CX, WMU; not I, GC, PO or TMC [13]
Number allowedOne ADU per lot with a single-family, two-family or multi-family dwelling [2]
TypesInside the house, attached addition, or detached [3]
Detached ADU setbacks5 ft interior side, 10 ft rear [4]
Detached ADU locationNot between the house and the front lot line [5]
Detached ADU heightNo taller than the house (over a garage: up to 25 ft or the house height, whichever is greater) [6]
Max size800 sq ft or 80% of the main unit, whichever is less [7]
ParkingNone required [8]
Sewer impact fee (April 2024 handout; may have changed)$1,980 for 1 bedroom, $2,970 for 2 [10]

Where ADUs are allowed

Bath's new Land Use Code, adopted September 2, 2026 and in effect since September 23, 2026, allows one accessory dwelling unit on any lawful lot with a single-family, two-family or multi-family dwelling [2]. In the use matrix (Table 8-1), a filled dot means a use is permitted (some projects may still need site plan approval) and a blank means it isn't [12]. The ADU row has a filled dot under all six residential districts (R-R, R-T, R-C, R-UC, R-WM, R-WH) and the NC, CC, DB, CG, MC, CX and WMU districts, and is blank under I, GC, PO and TMC [13]. An ADU needs a permit from the Codes Enforcement Officer, and if it would create a subdivision, subdivision approval comes first [1]. The code has no owner-occupancy requirement for ADUs.

Size, placement and height

An ADU can be inside an existing house, an attached addition, or a detached building [3]. It's exempt from building coverage and minimum lot area limits, except in the Shoreland Zone [2]. Additions follow the house's setbacks. A detached ADU needs only 5 feet from an interior side line and 10 feet from the rear line [4], and can't sit between the house and the front lot line [5]. It can't be taller than the house, unless it's built on top of an existing garage, where the limit is 25 feet or the house height, whichever is greater [6]. Maximum size is 800 square feet or 80% of the main dwelling unit, whichever is less [7]. No parking is required [8]. If you're on a well, you must show the water is potable before anyone moves in.

Building, fire and sewer

The Codes Office's ADU handout (April 2024) still explains building and fire rules: an ADU in or added onto a single-family house needs one-hour fire-rated walls and ceilings between the units [11]. A sewer impact fee is due with the building permit; the April 2024 handout lists $1,980 for one bedroom and $2,970 for two, so confirm the current amount [10], and a detached ADU needs its own sewer line and sewer permit.

Outdated handout numbers

The handout predates the new code. Its zoning rules (850 square feet, a 90-day minimum rental, two parking spaces for an ADU at a two-family house, and its reference to section 11.40) no longer apply. The new code has no ADU rental-length rule.

See how Bath compares with 8+ other Maine towns on accessory dwelling units (adus) →

Next steps

  1. Check your zoning district on the City's zoning map (updated 9-23-26) and whether the lot is in the Shoreland Zone, where lot coverage limits still apply.
  2. Sketch the plan: size (800 sq ft or 80% of the main unit, whichever is less), and for a detached ADU, 5 ft from side and 10 ft from rear lines and not in front of the house.
  3. Apply to the Codes Enforcement Office (City Hall, 55 Front Street, 207-443-8334) for the ADU and building permit, with a scaled site plan.
  4. Budget for the sewer impact fee and, for a detached ADU, a separate sewer line and sewer permit; confirm current fees with the Codes Office.

Common questions

Can I build an ADU in Bath, Maine?
Yes. Since September 23, 2026, Bath's Land Use Code allows one accessory dwelling unit on a lot with a single-family, two-family or multi-family home, inside the house, as an addition or as a detached building, with a permit from the Codes Enforcement Officer. ADUs are allowed in all six residential districts and the NC, CC, DB, CG, MC, CX and WMU districts.
How big can an ADU be in Bath, Maine?
No larger than 800 square feet or 80% of the main dwelling unit, whichever is less. A detached ADU can't be taller than the house, except one built on top of an existing garage, which can reach 25 feet or the house height, whichever is greater.
What are the setbacks for a detached ADU in Bath, Maine?
A detached ADU must be at least 5 feet from an interior side lot line and 10 feet from the rear lot line, and it can't sit between the house and the front lot line. An ADU built as an addition follows the house's setbacks.
Does an ADU in Bath, Maine need parking or an owner living on site?
No. Bath's Land Use Code requires no parking for an ADU and has no owner-occupancy requirement.
How much is the sewer impact fee for an ADU in Bath, Maine?
The Codes Office's April 2024 ADU handout lists $1,980 for one bedroom and $2,970 for two, paid with the building permit. Those are 2024 figures that may have changed, so confirm the current amount with the Codes Office. A detached ADU also needs its own sewer line and sewer permit.

Maine's statewide ADU law

Under 30-A M.R.S. §4364-B (first passed as LD 2003 in 2022), a town must allow at least one accessory dwelling unit (ADU) on a lot with a single-family home anywhere homes are allowed. Towns had to comply by 2024.

Rules in effect now:

  • It can be inside the house, attached, or a new detached building.
  • One ADU per lot is exempt from density limits.
  • No extra parking can be required beyond what the house already needs.
  • Setbacks are the same as for the house.
  • Minimum size: the state building codes board set 160 sq ft in 2025. Towns may set a maximum size.
  • Before you can move in, you must show the ADU has adequate water and septic/sewer.
  • In the shoreland zone ADUs must meet shoreland rules, but towns can't ban them there outright.
  • Sprinklers aren't required unless the ADU is in or attached to a building with more than 2 units.

Coming July 1, 2027 (LD 1829 of 2025, pushed back by LD 2173 in 2026): towns can no longer require the owner to live on the property, ADUs must also be allowed next to 2- and 3-unit buildings, and towns can't require planning board approval for an ADU. Towns may still regulate short-term rentals in ADUs. Private covenants and HOA rules can be stricter.

State sources: 30-A M.R.S. §4364-B (Accessory dwelling units) · 30-A M.R.S. §4364 (implementation dates) · 25 M.R.S. §2463-B (sprinklers in ADUs) · LD 2173 (P.L. 2025, c. 733) status and chaptered law · Maine Office of Community Affairs, Housing Legislation Guidance (March 2026)

What the ordinance says

Exact text from Bath's published ordinances. Section numbers are as printed in the source.

  1. LUC §8.4.A.1.a, City of Bath Land Use Code (new code adopted by City Council 2026-09-02, effective 2026-09-23), p. 97
    Accessory dwelling units (ADU) require a permit from the Codes Enforcement Officer. If the creation of an ADU creates a subdivision, the project will require subdivision approval before a building permit can be issued.
  2. LUC §8.4.A.1.b, City of Bath Land Use Code (new code adopted by City Council 2026-09-02, effective 2026-09-23), p. 97
    One accessory dwelling unit (ADU) is permitted on any lawfully conforming or nonconforming lot with a single-family, two-family, or multi-family dwelling. An ADU is exempt from building coverage and minimum lot area requirements unless located in the Shoreland Zone, in which case such requirements continue to apply.
  3. LUC §8.4.A.1.c, City of Bath Land Use Code (new code adopted by City Council 2026-09-02, effective 2026-09-23), p. 97
    ADUs are permitted within an existing conforming or nonconforming principal building, as additions sharing a common wall with a principal building, or as detached accessory structures.
  4. LUC §8.4.A.1.d, City of Bath Land Use Code (new code adopted by City Council 2026-09-02, effective 2026-09-23), p. 97
    Detached ADUs shall not be subject to side and rear setbacks for principal buildings or accessory structures, but shall maintain a minimum interior side setback of five feet, and a minimum rear setback of 10 feet.
  5. LUC §8.4.A.1.e, City of Bath Land Use Code (new code adopted by City Council 2026-09-02, effective 2026-09-23), p. 97
    Detached ADUs may not be located between any principal building and a front lot line.
  6. LUC §8.4.A.1.f, City of Bath Land Use Code (new code adopted by City Council 2026-09-02, effective 2026-09-23), p. 97
    The height of a detached ADU may not exceed the height of the primary structure, unless constructed as a vertical addition to an existing garage, in which case the height of the structure is limited to 25 feet or the height of the principal structure, whichever is greater.
  7. LUC §8.4.A.1.g, City of Bath Land Use Code (new code adopted by City Council 2026-09-02, effective 2026-09-23), p. 97
    ADUs are limited to a maximum gross floor area of 800 square feet or 80% of the size of the principal dwelling unit, whichever is less.
  8. LUC §8.4.A.1.h, City of Bath Land Use Code (new code adopted by City Council 2026-09-02, effective 2026-09-23), p. 97
    No parking is required for an accessory dwelling unit.
  9. LUC §8.6 Use Definitions, Accessory Dwelling Unit (ADU), City of Bath Land Use Code (new code adopted by City Council 2026-09-02, effective 2026-09-23), p. 103
    Accessory Dwelling Unit (ADU). An additional dwelling unit associated with and incidental to a principal dwelling on the same lot.
  10. CEO handout, Accessory Dwelling Units (4-8-24), sewer, CEO handout - Accessory Dwelling Units (2024-04-08), p. 1
    ADUs on City sewer that tie into a building’s existing sewer piping do not require a new sewer line to the City main, or a sewer permit, but do require payment of a sewer impact fee, which is a one time payment at the time of the building permit application, based on the number of bedrooms in the ADU (up to two are allowed) that helps fund the operation and upgrading of the City’s sewer system ($1980 for one bedroom, $2970 for two bedrooms).
  11. CEO handout, Accessory Dwelling Units (4-8-24), fire separation, CEO handout - Accessory Dwelling Units (2024-04-08), p. 1
    Creating an ADU in, or by adding on to an existing single- family house requires the dwelling units to be separated from each other with one hour fire rated walls and ceilings.
  12. LUC Table 8-1 Use Matrix, legend, City of Bath Land Use Code (new code adopted by City Council 2026-09-02, effective 2026-09-23), p. 79
    ⏺ = Permitted Use (May require Site Plan Approval) // ◐ = Permitted subject to Site Plan Approval by the Planning Board // Blank = Not Permitted
  13. LUC Table 8-1 Use Matrix, Accessory Uses rows (read by column), City of Bath Land Use Code (new code adopted by City Council 2026-09-02, effective 2026-09-23), p. 79
    Accessory Dwelling Unit (ADU) § 8.4.A Home Occupation § 8.4.C R-R ⏺ ⏺ R-T ⏺ ⏺ R-C ⏺ ⏺ R-UC ⏺ ⏺ R-WM ⏺ ⏺ R-WH ⏺ ⏺ NC ⏺ ⏺ CC ⏺ ⏺ DB ⏺ ⏺ CG ⏺ ⏺ MC ⏺ ⏺ CX ⏺ ⏺ WMU ⏺ ⏺ I GC PO TMC
This page summarizes Bath's posted ordinances as of 2026-10-19. Ordinances are amended, and individual lots can have overlays, subdivision covenants, or HOA rules that are stricter. Confirm with Codes Enforcement Office (City Hall, 55 Front Street; Mon-Thu 7:30 AM-5:00 PM). Planning & Development: 207-443-8363 (207-443-8334) before you build. Spot an error?