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Garage Conversion ADU on the North Shore

A garage already has a foundation, walls and a roof, which can make it a practical start for an ADU. The work is in the details: insulating a slab, adding windows and an entrance, and running water, sewer or septic and power. We connect you with independent local builders who can quote it.

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Former garage converted into a small apartment with a new door and windows

Why the 2025 ADU law matters

The rules changed statewide. Here is what that means for a North Shore lot.

Allowed by right

Since February 2, 2025, one ADU per lot is allowed by right in single-family zoning districts. Towns cannot require a special permit for a protected ADU.(Mass.gov: Accessory dwelling units (ADUs))

No owner-occupancy or family requirement

Towns cannot require the owner to live on the property or require that the ADU be occupied by family.(Mass.gov: Accessory dwelling units (ADUs), 760 CMR 71.00: Protected use accessory dwelling units)

Size and entrance rules

A protected ADU can be no larger than half the main house's gross floor area or 900 square feet, whichever is smaller, and must have its own entrance.(760 CMR 71.00: Protected use accessory dwelling units)

Local rules still apply

Towns may still use site plan review, setbacks and dimensional rules, short-term rental limits, and Title 5 septic requirements.(Mass.gov: Accessory dwelling units (ADUs), MassDEP: Guidance on Title 5 compliance for accessory dwelling units (PDF))

From idea to move-in

  1. Assess the structure. The builder checks the slab, framing, roof and whether the space can meet ceiling height, insulation and egress rules.
  2. Plan utilities. Running a sewer or septic line and adequate power is often the biggest variable in cost.
  3. Permits. A building permit and trade permits; your town may also do site plan review.
  4. Convert. Insulation, windows, entrance, kitchen and bath, then final inspections.

Is this a good fit?

  • You have a garage you use for storage rather than cars
  • The garage is attached or close to the house
  • You want a single-level unit for an older relative
  • You want to keep the ADU footprint you already have
  • Your lot has little room for a new building

Further reading: Mass.gov: Accessory dwelling units (ADUs) · 760 CMR 71.00: Protected use accessory dwelling units · MassDEP: Guidance on Title 5 compliance for accessory dwelling units (PDF) · Mass.gov: Check a home improvement contractor registration · Mass.gov: When is a construction supervisor license required?

Every job is different. The pro you speak with will explain their own approach and pricing. North Shore ADU Pros does not perform, supervise, or guarantee any work.

ADU questions

Will I lose required parking by converting the garage?

The state rules limit how much parking a town can require for an ADU: no more than one space, and none within half a mile of a transit station. Ask your town how it applies to your existing house.

Is a garage conversion always cheaper than new construction?

Not always. A slab that needs work, or a long run to the sewer or septic system, can add cost. Get a feasibility visit before assuming.

How big can it be?

Under state rules a protected ADU can be no larger than half the gross floor area of the main house or 900 square feet, whichever is smaller.

How many ADUs have been approved in Massachusetts?

The state's Executive Office of Housing and Livable Communities reported 2,084 ADUs approved and 2,824 applications statewide from 2025 through the first half of 2026.

How much parking can a town require?

No more than one space for a protected ADU, and none if the lot is within half a mile of a commuter rail, subway, ferry or bus station.

Other ADU types

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