Skip links

Call Now To Schedule Your Consultation

Muggeo & Associates law firm logo
978-741-1177
Muggeo & Associates

Building an ADU in Massachusetts: Homeowner Checklist

Use this checklist to plan an accessory dwelling unit under the Massachusetts ADU law. It covers the legal and practical steps homeowners most often miss. For the rules themselves, see our Massachusetts ADU FAQ and ADU lawyer page.

1. Confirm Eligibility

  • Confirm your lot is in a zoning district that allows single-family homes and is outside Boston.
  • Confirm no other ADU already exists on the lot. Only one protected-use ADU is allowed per lot.
  • Calculate the size limit: one-half of the principal dwelling’s gross floor area or 900 square feet, whichever is smaller.
  • Check whether the lot is in a historic district, floodplain or aquifer overlay, which may carry additional rules.
  • Check whether any part of the lot is within one-half mile of a subway, commuter rail, ferry or bus station, which affects parking.

2. Review Title and Private Restrictions

  • Pull your deed and any recorded covenants, easements and restrictions from the Registry of Deeds.
  • If you belong to an HOA or your home is a condominium, review the governing documents. The state ADU law does not override them.
  • Confirm the location of easements, utility lines and lot boundaries before siting a detached unit.
  • Tell your mortgage lender and title insurer about the project if your loan documents require it.

3. Review Local Zoning

  • Read your city or town’s current ADU bylaw or ordinance and note when it was last amended.
  • Compare local setbacks, height and lot coverage to the most permissive standard for the principal dwelling, single-family homes or accessory structures in your district.
  • Identify any local rule that conflicts with state law, such as an owner-occupancy requirement, minimum lot size, special permit requirement or excess parking.
  • Ask the building department whether site plan review applies and what it requires.

4. Septic, Utilities and Building Code

  • If you are on a septic system, have a Title 5 professional confirm capacity for the added bedrooms.
  • Ask your water, sewer and electric providers about connection requirements and fees.
  • Confirm that a basement or attic conversion can meet State Building Code ceiling height, egress and fire separation requirements.
  • Plan for smoke and carbon monoxide alarms and any required fire separation between units.

5. Hire Professionals and Sign a Clear Contract

  • Use a contractor registered under the Massachusetts Home Improvement Contractor law, G.L. c. 142A, for work on an owner-occupied home of one to four units, and confirm the construction supervisor license.
  • Get a written contract with a detailed scope, price, payment schedule tied to milestones, start and completion dates, and change-order procedure.
  • Do not pay more than one-third of the contract price in advance.
  • Confirm the contractor’s liability and workers’ compensation insurance.
  • Ask your homeowner’s insurer how coverage changes during construction and after the unit is occupied or rented.

6. Permits and Inspections

  • Apply for the building permit and any other required permits before work begins.
  • Keep copies of all applications, plans, approvals and inspection reports.
  • If a permit is denied or conditioned on a rule you believe conflicts with state law, note the date of the decision. Appeal deadlines are short.
  • Obtain a certificate of occupancy before anyone moves in.

7. If You Will Rent the ADU

  • Use a written lease that complies with Massachusetts law.
  • Follow the security deposit law exactly if you collect a deposit or last month’s rent.
  • If the home was built before 1978 and a child under six will live in the unit, comply with the state lead paint law.
  • Check local short-term rental rules before listing the unit for stays of 31 days or less.
  • Expect the assessed value of the property, and your property tax, to change once the ADU is complete.

8. Family Arrangements

  • If relatives are contributing money to build an in-law unit, put the arrangement in writing, including what happens if the property is sold or the relative moves out.
  • Review how the ADU fits your estate plan and whether title or beneficiary designations should change.

Planning an ADU or facing a permit problem? Contact Muggeo & Associates or call (978) 741-1177. Our Salem office serves homeowners across the North Shore and Massachusetts.

This page is general information, not legal advice. ADU rules depend on your city or town, your lot, and the structure involved, and local bylaws and state guidance continue to change. Contacting the firm does not create an attorney-client relationship. Prior results do not guarantee future outcomes. Last reviewed November 2026.