Accessory Structures in Portland, ME: What Residents Actually Need to Know

If you live in Portland or are thinking about moving there, accessory structures are one of those things you probably won't think about until they affect you directly. Portland has 2 specific rules on the books covering different aspects of accessory structures, and some of them might surprise you.

Shed & Carport Rules

A small shed or detached accessory structure of 250 square feet or less can sit as close as 5 feet to the rear lot line in Portland's RN-1 through RN-4 zones (3 feet in RN-6), with interior side setbacks as tight as 3 feet in RN-3/RN-4, and its height is capped at 18 feet under Land Use Code Table 7-A.

Key details: Rear setback, ≤250 SF shed (RN-1–4): 5 ft.. Rear setback, ≤250 SF shed (RN-6): 3 ft.. Side setback, ≤250 SF shed (RN-1/2): 5 ft.. Side setback, ≤250 SF shed (RN-3/4): 3 ft.. Max accessory structure height: 18 ft. (RN-1–RN-3).

Erecting or enlarging an accessory structure that violates Table 7-A's setback or height standards is a Land Use Code violation under § 1.5.2, punishable under Code of Ordinances § 1-15 by a fine of $100 to $500 per offense, with each day the violation continues counted separately. Building a shed without first obtaining the Chapter 6 permit exposes the owner to the same escalating per-day penalties and to a stop-work order under § 6-95(a) halting further construction until it is remedied.

ADU Rules

Portland's Land Use Code lets homeowners build up to two accessory dwelling units per qualifying property, by right, on any lawfully conforming or nonconforming lot with an existing legal residential use. A detached ADU tops out at 18 feet, 25 feet if built over a garage, and its floor area can't exceed two-thirds of the largest principal unit's gross floor area, effective under the Land Use Code that took effect July 1, 2026.

Key details: Max ADUs per lot: Two. Detached ADU height limit: 18 ft (25 ft over garage). ADU size cap: 2/3 of largest principal unit's floor area. Lot coverage/min lot area: ADUs exempt. General code penalty: $100–$500 per offense, per day.

Building or occupying an ADU that doesn't conform to Section 6.6.2(A), oversized, too tall, or sited in the front setback, is a Land Use Code violation under Section 1.5.2, enforced by the Building Authority or a City Code Enforcement Officer. Violators face the general penalty in Code of Ordinances Section 1-15: a fine of not less than $100 nor more than $500 per offense, with each day of continuing violation counted as a separate offense.

The Bottom Line

Portland's accessory structures rules are a mixed bag. Some areas are strict, others are relaxed, and the details matter. The best approach is to check the specific rule that applies to your situation rather than assuming Portland is broadly strict or permissive.

This guide is based on Portland's current municipal code. Local rules can and do change, so check the individual ordinance pages for the latest details, penalties, and FAQs.