Key Requirements
Permit Type
By Right
Permit Authority
Inspectional Services Department
Local Terminology
ADU
Max Size (sq ft)
900
Max Size (% of principal)
50%
Size Rule
Whichever is smaller
Attached Allowed
Yes
Detached Allowed
Yes
Internal Allowed
Yes
Parking Spaces Required
1
Transit Exemption
Yes
Short-Term Rental
Not addressed
Owner Occupancy Required
No
Design Review Required
—
Historic District Review
—
Energy Code
Stretch Code
HERS Rating Required
Yes
Max HERS Index (ADU)
52
Quick Summary
- Lynn allows ADUs under Massachusetts state law defaults -- the city does not have a dedicated local ADU ordinance or specific ADU bylaw section.
- One ADU per single-family lot, allowed by right with a standard building permit.
- Maximum 900 sq ft or 50% of the principal dwelling, whichever is smaller.
- No owner-occupancy, no family-member restrictions, no special permit required.
- Groundwater Protection District may affect ADU development in certain areas of the city -- check if your property falls within this district before proceeding.
Requirements at a Glance
| Requirement | Rule |
|---|---|
| Permit type | By right (building permit) |
| Max size | 900 sq ft or 50% of principal dwelling, whichever is smaller |
| Attached allowed | Yes |
| Detached allowed | Yes |
| Internal allowed | Yes |
| Parking | 1 space max; 0 spaces if within 0.5 miles of transit |
| Owner occupancy | Not required |
| Family member restriction | None |
| Short-term rental | Not addressed in available sources |
| Affordability | No affordability requirement |
| Design standards | Standard building/safety/zoning requirements |
| Groundwater district | May impose additional limitations -- check property |
ADU Questions in Lynn
Can I build an ADU in Lynn, MA?
Yes. Accessory dwelling units are allowed by right in Lynn, MA, meaning you do not need a special permit or a zoning variance as long as the unit meets the town's dimensional rules. You still need a building permit from the Inspectional Services Department. Lynn calls these "ADU."
How big can an ADU be in Lynn, MA?
Lynn limits an accessory dwelling unit to 900 square feet or 50% of the principal dwelling, whichever is smaller. State law protects ADUs up to 900 square feet on single-family lots, so a town cannot enforce a smaller cap on a protected-use ADU.
What types of ADU are allowed in Lynn, MA?
Lynn permits 3 forms of accessory dwelling unit: detached (a separate structure in the yard); attached (an addition to the house); internal (a conversion of existing space). Which one makes sense usually comes down to your lot, your septic or sewer situation, and whether you want the unit connected to the main house.
Does Lynn, MA require extra parking for an ADU?
Lynn's bylaw calls for 1 additional off-street parking space(s) for an ADU. Under state law, towns cannot require more than one space for a protected-use ADU, and no parking at all can be required within a half mile of transit.
Do I have to live on the property to rent out an ADU in Lynn, MA?
No. Lynn does not impose an owner-occupancy requirement, and state law bars towns from requiring it for protected-use ADUs. You can rent the unit without living on site.
What energy code applies to an ADU in Lynn, MA?
Lynn has adopted the Stretch Energy Code. That means a new ADU must hit a HERS rating of 52 or lower, which drives real decisions about insulation, air sealing, windows, and heating — typically an all-electric heat pump system. Budget for a HERS rater on the project from day one.
Based on Lynn’s bylaw as last verified 2026-02-25. Bylaws change at annual town meetings — confirm with the City of Lynn Inspectional Services Department before you build.