Portland ADU permit requirements
Last reviewed: June 22, 2026
Quick answer
Permitting an accessory dwelling unit (ADU) in Portland, Maine means pulling a building permit from the local authority that issues it. ArchPermit tracks 14 source-cited requirements (11 required, the rest conditional) for this jurisdiction. Submittals go through Citizen Self Service (CSS) portal (EnerGov, online only). These requirements were last reviewed June 22, 2026; confirm the exact forms and fees with the local permitting authority.
A source-cited checklist of what an ADU (accessory dwelling unit) permit package needs in City of Portland. Every item links to its authoritative source; items that vary are flagged to confirm locally.
(Portland, MAINE, not Portland, OR.) Maine's statewide ADU law (LD 2003 / 30-A M.R.S. § 4364-B) requires every municipality to allow at least one ADU on any lot where a single-family dwelling is the principal structure (within, attached, or a new detached structure), with no additional parking, a minimum size of 190 sf, and, per a 2025 amendment, construction/occupancy even if the owner does not reside on the lot. Portland's Land Use Code § 6.6.2.A allows up to two ADUs per qualifying property; an ADU is ≤2/3 of the principal unit's gross floor area; a detached ADU may not exceed the primary structure's height; and owner-occupancy of one unit is required at initial creation (now in tension with the 2025 state amendment; confirm with Zoning). There is no standalone ADU checklist: a conversion/attached ADU uses the Residential Additions checklist; a new detached ADU uses the New Single/Two-Family checklist (Minor Site Plan Review). Trade permits are separate and come after the building permit; new dwellings need NFPA 13D sprinklers.
- CSS Online Application (EnerGov)required
Completed permit application submitted online via the Citizen Self Service portal (the only accepted method).
source · reviewed 2026-06-22 - Cross Sections & Framing Plansrequired
Foundation/anchor/rebar/drainage details; floors/walls/beams/ceilings/rafters with materials, sizes, spans, spacing, and connection details; fire-rated assemblies between units.
source · reviewed 2026-06-22 - Elevations (existing & proposed)required
Dimensioned exterior elevations; for new construction include height from average grade and all four sides.
source · reviewed 2026-06-22 - Energy Code Compliance / ResCheckrequired
Insulation type and R-values for walls/ceilings/foundations/floors; new construction additionally requires ResCheck certificates per the adopted IECC.
source · reviewed 2026-06-22 - Floor Plans (existing & proposed)required
To scale and dimensioned for the entire building; label rooms/floors; show escape windows and smoke/CO detection.
source · reviewed 2026-06-22 - Foundation Planrequired
Footing or pier (sonotube) sizes, location, and depth.
source · reviewed 2026-06-22 - General Building Permit Application (signed)required
Address/CBL, owner & applicant info, current/proposed use, cost of work, project description, and signature/authorization.
source · reviewed 2026-06-22 - Plot / Site Plan (to scale)required
Lot shape/dimensions; existing & proposed structures; distances between structures and to property lines; parking and driveways.
source · reviewed 2026-06-22 - Separate Trade Permits (plumbing, electrical, fire sprinkler, HVAC)required
Obtained separately and only after the main building permit is issued; new dwellings require NFPA 13D sprinklers.
source · reviewed 2026-06-22 - Water/Wastewater Written Verification (pre-CO)required
Per state law, the owner must give written verification of adequate water & wastewater service before the ADU may be certified for occupancy.
source · reviewed 2026-06-22 - Window & Door Schedulesrequired
Window schedule (egress dims, safety glazing, U-factors) and door schedule (type, size, fire rating, U-factors).
source · reviewed 2026-06-22 - Boundary Survey (new detached ADU)conditional
Meeting Section 13 of the City Technical Manual. Required for a new single-/two-family dwelling (new detached ADU); hand-drawn footprints not accepted.
source · reviewed 2026-06-22 - Impact Fee Form (+ Portland Water District documentation)conditional
Parks/Rec, Transportation & Wastewater impact-fee form, triggered by the net increase in dwelling units; include the PWD water-meter capacity letter.
source · reviewed 2026-06-22 - Proof of Ownershipconditional
Deed or purchase & sale agreement, required only if the property was purchased within the past six months.
source · reviewed 2026-06-22
Portland ADU permit questions
- Do I need a permit to build an ADU in Portland?
- Yes. An accessory dwelling unit (ADU) in Portland requires a building permit. ArchPermit tracks 14 cited requirements for this jurisdiction (11 required, the rest conditional). Always confirm the exact forms, fees, and code edition with the local permitting authority that issues the permit.
- What does an ADU permit package require in Portland?
- Core required items include: CSS Online Application (EnerGov); Cross Sections & Framing Plans; Elevations (existing & proposed); Energy Code Compliance / ResCheck; Floor Plans (existing & proposed); Foundation Plan, plus 5 more. Each requirement links to its authoritative source, and nothing is permit-ready until an independent licensed professional reviews and seals it.
- How are ADU permits submitted in Portland?
- Portland accepts permit submittals via Citizen Self Service (CSS) portal (EnerGov, online only). ArchPermit prepares a draft package you can submit there after a licensed architect reviews and seals it.