Maine · New Hampshire
ADU rules by town
Each town below links to what its own zoning ordinance says about accessory dwelling units, with the section number and a link to the ordinance. 49 towns are listed.
Towns marked “town page” or “in our service area” are places we work. Reference guides cover nearby towns outside that list; call to ask about a build in one of them.
State law sets the floor in both states. See Maine’s 2027 rules and New Hampshire’s RSA 674:72.
Maine
| Town | ADU size limit | Owner on site | Read |
|---|---|---|---|
| ActonYork County · town page | Up to 800 sq ft | Required by the town text; Maine law bars this from July 1, 2027 | 2026-11-15 |
| AlfredYork County · town page | 190 to 576 sq ft attached; up to 400 sq ft detached | Required by the town text; Maine law bars this from July 1, 2027 | 2026-11-15 |
| BerwickYork County · in our service area | More than 190 sq ft; no town maximum | No town rule | 2026-11-15 |
| BiddefordYork County · reference guide | 300 sq ft minimum; maximum 35% of the house's gross floor area or 900 sq ft, whichever is greater; max two bedrooms | Owner must live in the house or the ADU | 2026-11-15 |
| EliotYork County · reference guide | 190 sq ft min; max 1,000 sq ft or 50% of the house, whichever is less; max 2 bedrooms | Owner must live in the house or the ADU as principal residence; recorded covenant required | 2026-11-15 |
| KennebunkYork County · town page | 190 to 1,000 sq ft | More than 6 months a year, required by the town text; Maine law bars this from July 1, 2027 | 2026-11-15 |
| KennebunkportYork County · in our service area | 190 to 800 sq ft of living area | No owner rule; ADU must be someone's primary residence (more than 6 months a year) | 2026-11-15 |
| KitteryYork County · reference guide | Building-code minimum; max 1,000 sq ft (80% of the house if the house is 1,000 sq ft or smaller); max 2 bedrooms | No town rule (the parcel owner must apply) | 2026-11-15 |
| LebanonYork County · town page | No town limit found; state minimum 190 sq ft | No town rule found | 2026-11-15 |
| LimerickYork County · town page | Up to 900 sq ft and 2 bedrooms | No town rule | 2026-11-15 |
| NewfieldYork County · town page | 190 to 750 sq ft | No town rule | 2026-11-15 |
| North BerwickYork County · in our service area | 190 to 650 sq ft; max one bedroom, two occupants | No town rule | 2026-11-15 |
| SacoYork County · reference guide | 400 to 1,000 sq ft of total floor area | No town rule | 2026-11-15 |
| SanfordYork County · town page | 1,000 sq ft or 40% of the house, whichever is greater; up to 3 bedrooms | Required by the town text; Maine law bars this from July 1, 2027 | 2026-11-15 |
| ShapleighYork County · town page | 190 to 800 sq ft | Required by the town text; Maine law bars this from July 1, 2027 | 2026-11-15 |
| South BerwickYork County · in our service area | 190 sq ft min; 750 sq ft max living area | Owner must live in the house or the ADU | 2026-11-15 |
| WaterboroYork County · town page | 410 to 800 sq ft in the town text (state minimum 190) | Required by the town text; Maine law bars this from July 1, 2027 | 2026-11-15 |
| WellsYork County · town page | 190 to 800 sq ft (detached at least 400) | Required by the town text; Maine law bars this from July 1, 2027 | 2026-11-15 |
| YorkYork County · town page | 190 sq ft up to 850 sq ft or half the house, whichever is smaller | Part of each year under a recorded covenant, required by the town text; Maine law bars this from July 1, 2027 | 2026-11-15 |
New Hampshire
| Town | ADU size limit | Owner on site | Read |
|---|---|---|---|
| AltonBelknap County · town page | Detached up to 950 sq ft; attached up to 1,500 sq ft or 35% of the house, never below 750 | Required | 2026-11-15 |
| BarringtonStrafford County · reference guide | Up to 1,000 sq ft inside or attached to the house; up to 750 sq ft finished floor in a detached accessory structure; max 2 bedrooms | Owner must live in one of the two units | 2026-11-15 |
| ConwayCarroll County · town page | 300 to 1,000 sq ft (a second ADU up to 850) | No owner rule | 2026-11-15 |
| DoverStrafford County · town page | 300 to 950 sq ft | Required in one of the two units | 2026-11-15 |
| DurhamStrafford County · town page | 300 to 850 sq ft | Required, 3 of any 5 years | 2026-11-15 |
| EffinghamCarroll County · in our service area | Max 1,200 sq ft gross floor area (open decks excluded); max 2 bedrooms | Owner must live in the house or the ADU | 2026-11-15 |
| ExeterRockingham County · town page | Detached up to 750 sq ft; in the house up to half its floor area, never below 750 | Required | 2026-11-15 |
| FarmingtonStrafford County · in our service area | 350 to 950 sq ft; max 2 bedrooms | Owner must live in the house or the ADU; restrictive covenant recorded | 2026-11-15 |
| FreedomCarroll County · in our service area | Max 800 sq ft total living space; max 2 bedrooms | Owner must live in the house or the ADU | 2026-11-15 |
| GilfordBelknap County · town page | 300 to 1,000 gross sq ft and 2 bedrooms | No owner rule | 2026-11-15 |
| GreenlandRockingham County · reference guide | Max 1,200 sq ft of conditioned space, max two bedrooms | Owner must live in one of the units | 2026-11-15 |
| HamptonRockingham County · town page | Up to 1,000 sq ft and 2 bedrooms | Required; deed amendment in RA and RAA | 2026-11-15 |
| LaconiaBelknap County · town page | 300 to 1,000 sq ft (25% of a house over 4,000 sq ft) | Required, 200 days a year | 2026-11-15 |
| LeeStrafford County · reference guide | 200 to 1,000 sq ft gross floor area; not larger than the main house, but never capped below 750 sq ft; max 2 bedrooms | Owner must live in the house or the ADU (proof by Lee voter or vehicle registration) | 2026-11-15 |
| MadburyStrafford County · in our service area | Max 50% of the principal dwelling's finished living area | Owner must occupy the house or the ADU | 2026-11-15 |
| MeredithBelknap County · town page | 300 sq ft up to 40% of floor area or 1,200 sq ft, whichever is less | No owner rule (removed in 2026) | 2026-11-15 |
| MiltonStrafford County · in our service area | Max 1,000 sq ft (town may not cap below 750 sq ft); max 2 bedrooms; max 4 occupants | Owner must live in the house or the ADU; only one unit may be rented | 2026-11-15 |
| MoultonboroughCarroll County · town page | Up to 1,100 sq ft and 2 bedrooms | Required | 2026-11-15 |
| New DurhamStrafford County · in our service area | Max 1,000 sq ft gross living area (750 sq ft if the main house is under 1,000 sq ft); max 2 bedrooms | No town rule | 2026-11-15 |
| NewmarketRockingham County · reference guide | 200 to 1,000 sq ft gross floor area; no more than 80% of the house, but never capped below 750 sq ft; +100 sq ft bonus for rooftop solar | Owner must live in the house or the ADU (voter or vehicle registration as proof) | 2026-11-15 |
| North HamptonRockingham County · reference guide | Footprint of all ADU floors combined max 800 sq ft; minimum 720 sq ft ground-floor or lower living area; max two bedrooms | Owner must live in the house or the ADU | 2026-11-15 |
| OssipeeCarroll County · town page | Up to 1,200 sq ft | Required | 2026-11-15 |
| PortsmouthRockingham County · town page | Up to 750 sq ft and 2 bedrooms | Required | 2026-11-15 |
| RochesterStrafford County · town page | Up to 800 sq ft and 2 bedrooms | Required | 2026-11-15 |
| RollinsfordStrafford County · in our service area | Max 750 sq ft of living space and 2 bedrooms | Owner must live in one of the units as a principal residence | 2026-11-15 |
| SomersworthStrafford County · in our service area | Max 800 sq ft habitable space and 1,200 sq ft gross; max 2 bedrooms | Owner must occupy one of the two units | 2026-11-15 |
| StrathamRockingham County · reference guide | 400 to 1,000 sq ft, max two bedrooms; a detached ADU is also capped at 50% of the house's gross interior area and a 1,000 sq ft building footprint | Owner must live in either unit | 2026-11-15 |
| TuftonboroCarroll County · in our service area | No town sq ft cap; ADU must be subordinate in size to the house (state default 950 sq ft max applies) | Owner must live in the house or the ADU; certified at building permit and in writing each year | 2026-11-15 |
| WakefieldCarroll County · town page | 300 to 950 sq ft | 4 consecutive months a year | 2026-11-15 |
| WolfeboroCarroll County · town page | 750 sq ft or 30% of the house, whichever is larger | Required | 2026-11-15 |
Want the rules read for your lot?
Call (978) 987-0089 with the address.