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Can I build an ADU in Rockport, Maine?

Rockport, Knox County · Ordinances checked 2026-10-01 · Reviewed · 9 cited sections

Allowed with a permit

Yes. Rockport allows one accessory dwelling unit on any lot where a single-family home is the principal building, inside the house, attached, or as a new detached building, with a building permit from the Code Enforcement Officer. The ADU must be at least 190 square feet, a detached one can't be taller or larger than the main house, and the ordinance currently requires the owner to live in either the house or the ADU.

ADUs per single-family lot1 [2]
Types allowedInside the house, attached, detached new building, or converted accessory structure [1]
Detached ADU size/heightNo taller and no larger in floor area than the main house [1]
Minimum ADU size190 sq ft [5]
Owner-occupancyOwner must live in the house or the ADU as principal residence [3]
Extra parkingNone beyond the single-family requirement (1 extra space in Traditional Village District) [4]
ApprovalBuilding permit from the Code Enforcement Officer [7]

Where and what kind

Rockport's Land Use Ordinance (amended June 9, 2026) allows an ADU inside an existing single-family home, attached to it, or as a new detached building on a single-family lot, and existing accessory structures such as garages can be converted [1]. One ADU may be added to any lot where a single-family home is the principal structure [2]. The Land Use Table lists Accessory Dwelling Unit as a permitted use (P) in the Harbor Village, Village, Residential Coastal, Residential, both Mixed Business/Residential, Rural, and Hospital and Resort districts, but not in the Downtown or Industrial districts [9]. Single-family homes are permitted in Downtown, and state law requires towns to allow an ADU wherever single-family homes are allowed, so §815(2)(f) and state law may override that gap.

Size and dimensions

A new detached ADU may not exceed the height or floor area of the main house and must be subordinate to it [1]. Every ADU must be at least 190 square feet [5]; the ordinance sets no separate maximum square footage beyond that subordinate-to-the-house rule. (A 2025 state building-codes rule set a 160 sq ft minimum, so ask whether Rockport still applies 190.) An ADU is exempt from density requirements and the lot coverage calculation, but single-family setbacks and dimensional requirements still apply to both the house and the ADU [4].

Owner-occupancy

The ordinance requires that either the main house or the ADU be occupied by the property owner as their principal residence [3]. State law will bar towns from requiring owner-occupancy for ADUs starting July 1, 2027, so this provision may no longer be enforceable after that date.

Parking

No parking is required for the ADU beyond what the single-family home needs [4]. However, the Traditional Village District's special parking standards call for one space for an ADU in addition to the principal use [8], so ask the town which rule it applies there.

Utilities, shoreland and permits

Before the town certifies the ADU for occupancy, you must give written verification that it is connected to adequate water and wastewater service; septic systems must be verified by the local plumbing inspector [6]. ADUs in the shoreland zone must also meet the Chapter 1400 shoreland standards. No structure may be built, added to or substantially renovated without a permit from the Code Enforcement Officer [7], and a Certificate of Occupancy is required before occupying it.

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

Next steps

  1. Confirm your zoning district and whether the lot is in the Shoreland Zoning Overlay with Rockport Planning & Codes (207-236-0989 ext. 2).
  2. Prepare a site plan showing the ADU's location and dimensions and confirm it meets single-family setbacks; for a detached ADU, confirm it is smaller and no taller than the house.
  3. Get septic adequacy confirmed by the local plumbing inspector (or proof of sewer/water service capacity and connection payment).
  4. Apply to the Code Enforcement Officer for a building permit, then obtain a Certificate of Occupancy before anyone moves in.

Common questions

Can I build an ADU in Rockport, Maine?
Yes. Rockport allows one accessory dwelling unit on any lot where a single-family home is the principal building, inside the house, attached, or as a new detached building. You need a building permit from the Code Enforcement Officer.
How big can an ADU be in Rockport, Maine?
An ADU must be at least 190 square feet. A detached ADU can't be taller or larger in floor area than the main house, and the ordinance sets no separate maximum beyond that.
Does the owner have to live on the property to have an ADU in Rockport, Maine?
Currently yes. The ordinance requires the owner to live in either the house or the ADU as their principal residence. State law bars towns from requiring this starting July 1, 2027, so it may not be enforceable after that.
Do I need extra parking for an ADU in Rockport, Maine?
No parking is required beyond what the single-family home needs. The page notes one extra space in the Traditional Village District.

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 Rockport's published ordinances. Section numbers are as printed in the source.

  1. §815(2)(a)-(e) Accessory Dwelling Units, Restrictions, Land Use Ordinance (June 9, 2026), p. 80
    c. As a new structure on a single family lot, for the primary purpose of creating an ADU. d. A newly constructed, detached ADU, shall not exceed the height nor floor area and shall be subordinate to the existing primary dwelling. e. Additionally, existing accessory structures can be converted into an ADU.
  2. §815(2)(f), Land Use Ordinance (June 9, 2026), p. 80
    f. One ADU is permitted to be added on any lot where a single-family dwelling unit is the principal structure, and
  3. §815(2)(h), Land Use Ordinance (June 9, 2026), p. 81
    h. Either the principal structure or converted ADU shall be occupied by the owner of the property as their principal residence.
  4. §815(3)-(4) Zoning Density Requirements; Parking, Land Use Ordinance (June 9, 2026), p. 81
    In reviewing an ADU, the setback and dimensional requirements for a single-family home continue to apply to the primary structure and the ADU, as specified in the dimension tables of Section 918. 4. Parking There are no additional parking requirements for the ADU, beyond those required for the single-family dwelling.
  5. §815(5) Accessory Dwelling Unit Size, Land Use Ordinance (June 9, 2026), p. 81
    ADUs must be at least 190 square feet in size.
  6. §815(7) Water and Wastewater, Land Use Ordinance (June 9, 2026), p. 81
    The owner of an ADU must provide written verification to the municipality that the ADU is connected to adequate water and wastewater services before the municipality may certify the ADU for occupancy.
  7. §601(1) Building Permits, Land Use Ordinance (June 9, 2026), p. 38
    No structure shall be constructed, moved, added to, or substantially renovated without a permit issued by the Code Enforcement Officer.
  8. §910, Special Parking Standards for a Traditional Village, Land Use Ordinance (June 9, 2026), p. 102
    a) For an Accessory Dwelling Unit, One (1) parking space shall be required, in addition to the spaces required for the principal use.
  9. §917(B) Land Use Table, Residential (P in columns 901, 902, 903, 904, 906, 907, 908, 909; blank in 913, 916), Land Use Ordinance (June 9, 2026), p. 109
    Accessory Dwelling Unit P P P P P P P P
This page summarizes Rockport's posted ordinances as of 2026-10-01. Ordinances are amended, and individual lots can have overlays, subdivision covenants, or HOA rules that are stricter. Confirm with Planning, Community and Economic Development, and Codes - Code Enforcement (207-706-4071 (CEO Andrew Lowe); 207-236-0989 ext. 2 (Planning & Codes clerk)) before you build. Spot an error?