Can I build an ADU in Lincoln, Massachusetts?
Yes. Lincoln's zoning bylaw grants a building permit for one attached or detached ADU per lot in any single-family district, up to 900 sq ft or half the main house's floor area, whichever is smaller. A detached ADU also needs Planning Board site plan review. A larger "accessory apartment" of up to 1,200 sq ft is also possible, but it comes with an owner-occupancy rule and a 40,000 sq ft minimum lot.
| Approval for one ADU | Building permit (by right), attached or detached [2] |
| Max ADU size | 900 sq ft or 1/2 of the main house's gross floor area, whichever is smaller [1] |
| Detached ADU | Planning Board site plan review required [3] |
| Parking | 1 space, none if within 0.5 mile of a transit station [4] |
| Minimum rental term | 7 days [5] |
| Accessory apartment max size | 1,200 sq ft (and 35% of combined floor area if inside the house) [6] |
| Accessory apartment lot size / occupancy | 40,000 sq ft lot; owner must live in the house or the apartment [7] |
Protected ADUs (Section 14.4)
Lincoln added Section 14.4 in 2025 to track the state ADU law. An ADU is a self-contained unit with its own sleeping, cooking and bathroom facilities and a separate entrance. It can't be larger than half the main house's gross floor area or 900 sq ft, whichever is smaller [1]. The Building Inspector grants a building permit for one ADU per lot in any single-family district, whether it's attached or detached [2]. Every detached ADU must first get Planning Board site plan approval under Section 17.7 [3]. If the lot or house is nonconforming, the Zoning Board of Appeals must make a finding first, but no special permit is needed.
Other conditions: the ADU can't be sold separately from the house; you file floor plans and a site plan; the ADU must meet normal setbacks and height limits; and the Board of Health must certify sewage disposal. You need one parking space unless the lot is within half a mile of a transit station [4]. If either unit is rented, the minimum rental term is seven days [5]. A second ADU or accessory apartment on the same lot needs a special permit from the Board of Appeals.
Accessory apartments (Section 14.3)
Lincoln's older accessory-apartment rules still apply to units bigger than an ADU. These are capped at 1,200 sq ft, and an apartment inside the house can't exceed 35% of the combined floor area [6]. The lot must be at least 40,000 sq ft, and the owner must live in either the main house or the apartment [7]. An apartment inside the house gets a building permit. One in a detached structure needs a special permit from the Board of Appeals after a public hearing.
State law
The owner-occupancy and lot-size rules apply only to the larger accessory apartments, not to Section 14.4 ADUs. State law protects ADUs of up to 900 sq ft, and its rules on what towns may require are shown separately. Whether a site plan requirement for every detached ADU counts as "reasonable" under state regulations hasn't been tested, so state law may limit that provision.
See how Lincoln compares with 8+ other Massachusetts towns on accessory dwelling units (adus) →
Next steps
- Confirm the house's gross floor area to work out your maximum ADU size (the smaller of 900 sq ft or half the house).
- For a detached ADU, apply to the Planning Board for site plan review under Section 17.7 and record the approval.
- Get a written Board of Health report confirming septic capacity for the added unit.
- Apply to the Building Department (781-259-2613) for a building permit with dimensional floor plans and a scaled site plan showing setbacks, height and the parking space.
Common questions
- Can I build an ADU in Lincoln, Massachusetts?
- Yes. Lincoln's zoning bylaw grants a building permit for one attached or detached ADU per lot in any single-family district. A detached ADU also needs Planning Board site plan review.
- How big can an ADU be in Lincoln, Massachusetts?
- Up to 900 sq ft or half the main house's floor area, whichever is smaller. A larger accessory apartment of up to 1,200 sq ft is possible, with an owner-occupancy rule and a 40,000 sq ft minimum lot.
- How long must I rent an ADU in Lincoln, Massachusetts?
- The bylaw sets a 7-day minimum rental term.
- Does an ADU need parking in Lincoln, Massachusetts?
- Yes, 1 space, though none is needed within 0.5 mile of a transit station.
Massachusetts' statewide ADU law
Since February 2, 2025, the Affordable Homes Act (St. 2024, c. 150, §8) has protected one accessory dwelling unit (ADU) per lot in any zoning district that allows single-family homes (M.G.L. c. 40A, §3). Your town cannot ban it, require a special permit or other discretionary approval, or "unreasonably restrict" building or renting it.
What counts as a protected ADU:
- A self-contained unit with its own sleeping, cooking and bathroom facilities, on the same lot as the main home.
- No larger than 900 sq ft or half the main home's floor area, whichever is smaller.
- It can be attached or detached, and it needs a separate entrance that meets the building code.
What towns cannot require:
- That the owner live in the main home or the ADU.
- More than 1 extra parking space, or any extra space if the lot is within 0.5 miles of a subway, commuter rail, ferry or bus station.
- A minimum lot size, caps on the number of ADUs, or limits on who may live there (age, income, relationship).
What towns can still do: use reasonable site plan review, setback, height and bulk rules, require Title 5 septic compliance, and restrict or ban short-term rentals of ADUs. A second ADU on the same lot needs a special permit. State regulations at 760 CMR 71.00 (in effect since January 31, 2025) explain which rules count as unreasonable.
What the bylaw says
- Sec. 14.4.1(a) Accessory Dwelling Unit (ADU), Zoning By-laws (latest amendment September 22, 2025), p. 86
(ii) is not larger in Gross Floor Area than ½ the Gross Floor Area of the Principal Dwelling or 900 square feet, whichever is smaller; and (iii) is subject to additional restrictions as may be imposed by this bylaw.
- Sec. 14.4.2 Requirements for Accessory Dwelling Units, Zoning By-laws (latest amendment September 22, 2025), p. 86
A building permit shall be granted for one Protected Use ADU on a Lot within a Single-Family Residential District whether attached or detached provided that the Protected Use ADU meets the requirements of this section.
- Sec. 14.4.2 Requirements for Accessory Dwelling Units, Zoning By-laws (latest amendment September 22, 2025), p. 86
Notwithstanding the threshold required for Site Plan Review pursuant to Sections 4.6 or 6.02, all proposed Protected Use ADUs that are detached from the Principal Dwelling shall be subject to Site Plan review pursuant to Section 17.7 and a recorded copy of such Site Plan Approval must be submitted to the Building Department as part of the building permit application.
- Sec. 14.4.2(f) Access and Parking, Zoning By-laws (latest amendment September 22, 2025), p. 87
One parking space shall be provided for the Protected Use ADU on the lot except where the Lot is located within a .5-mile radius of a Transit Station.
- Sec. 14.4.2(i) Minimal Rental Period, Zoning By-laws (latest amendment September 22, 2025), p. 87
(i) Minimal Rental Period: Where the ADU or the Principal Dwelling is occupied as a rental unit, the minimum occupancy or rental term shall be seven days.
- Sec. 14.3.2(a) Floor Area, Zoning By-laws (latest amendment September 22, 2025), p. 82
(a) Floor Area: the Accessory Apartment shall not exceed 1200 square feet, and (for a unit included in a single-family dwelling) shall not exceed 35% of the floor area of the principal dwelling unit and Accessory Apartment combined.
- Sec. 14.3.2(b)-(c) Lot Size; Occupancy, Zoning By-laws (latest amendment September 22, 2025), p. 82
(b) Lot Size: the lot on which the Accessory Apartment and principal dwelling unit are located shall contain at least 40,000 square feet. (c) Occupancy: either the Accessory Apartment or the principal residence is occupied by the owner of the lot on which the Accessory Apartment is to be located, except for bona fide temporary absences.