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