Side by side · Maine
Compare ADU rules across Maine
Flexible on where you build? The same backyard cottage can be routine in one city and impossible next door. This table puts 12 Maine cities side by side so you can shortlist the friendly ones before reading a single ordinance, or narrow it to just the cities you are deciding between. Every value is summarized from the city's own code; open a city's page for the full notes, citations, and fine print.
The short answers
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| City | Detached ADU | Attached / internal | Max size | Owner occupancy | Extra parking | Approval |
|---|---|---|---|---|---|---|
| Auburn | Allowed | Allowed | 1,500 sq ft maximum, 190 sq ft minimum; district height limit applies (2½ stories or 35 ft in the residential districts) | Not required | None for the ADU itself outside the Lake Auburn watershed (state preemption); Auburn's own table nominally reads 1 space per dwelling unit | Permitted use |
| Augusta | Allowed | Allowed | Up to the floor area of the primary structure (no fixed square-foot cap); minimum 190 sq ft | Not required | None: no off-street parking required for an ADU | Permitted use |
| Bangor | Allowed | Allowed | 1,000 sq ft or 50% of the principal dwelling, whichever is less (minimum 160 sq ft) | Not required | None | Permitted use |
| Bar Harbor | Allowed | Allowed | No maximum size; 190 sq ft minimum | Not required | None | Permitted use |
| Biddeford | Allowed | Allowed | 900 sq ft or 35% of the principal dwelling's gross floor area, whichever is greater; 300 sq ft minimum; max 2 bedrooms | Required | None enforceable (state preemption); the unamended ordinance still lists 1 off-street space unless on-street or public parking is within 1,000 feet | Permitted use |
| Brunswick | Allowed | Allowed | 1,100 sq ft, or 75% of the largest dwelling unit's gross floor area, whichever is less | Not required | None | Permitted use |
| Lewiston | Allowed | Allowed | 900 sq ft habitable area, max 2 bedrooms (190 sq ft minimum) | Required | None: no additional off-street parking required | Permitted use |
| Portland | Allowed | Allowed | Proportional, not a flat number: each ADU is capped at 2/3 of the gross floor area of the largest principal unit on the lot, and all detached ADUs together may not exceed the gross floor area of the principal structure. Detached ADUs are capped at 18 ft tall, 25 ft above a garage | Not required | None. Portland requires no off-street vehicle parking for any use citywide | Permitted use |
| Saco | Allowed | Allowed | 1,000 sq ft of total floor area (400 sq ft minimum) | Not required | None: no additional off-street parking for an ADU | Permitted use |
| Sanford | Allowed | Allowed | 1,000 sq ft or 40% of the principal dwelling's living area, whichever is greater; max 3 bedrooms | Required | None | Permitted use |
| Scarborough | Allowed | Allowed | 750 to 1,500 sq ft, scaled to the size of the house; 190 sq ft minimum | Required | None | Permitted use |
| South Portland | Allowed | Allowed | 800 sq ft on lots under 10,890 sq ft; 1,200 sq ft on larger lots, and never more than 10% of the lot or 90% of the primary dwelling; 190 sq ft minimum | Not required | None | Permitted use |
Summarized from each city's ordinance text, most recently read August 2026. Tap a value marked with an info icon to see exactly what it depends on, straight from the ordinance. Nearly every value has zone, lot-size, or process caveats beyond that; the per-city pages carry the full notes and code citations. Treat this as orientation, not a permit determination.
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Reading the table
- Detached ADU is the make-or-break column for backyard cottages: minimum lot sizes (often 8,000 to 14,500 sq ft) hide behind many of the "Allowed" values, so check your lot before celebrating.
- Attached / internal (basement apartments, additions) is legal almost everywhere and is usually the path of least resistance.
- Approval: "Permitted use" means staff-level sign-off; "Conditional use" means a public hearing, which adds time, cost, and uncertainty.
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