ADU Builders in Medford, MA (2026)

An ADU builder in Medford is a licensed contractor who designs and constructs accessory dwelling units — detached backyard units, garage conversions, attached additions, and junior ADUs (JADUs). Because an ADU is a complete second dwelling, the builder coordinates foundation, framing, plumbing, electrical, and HVAC work and pulls it through Medford's permit process and utility connections. Not every general contractor has built one, so the right builder is one with ADU-specific experience in Massachusetts.

What ADU Builders Cost in Medford ^[16]^[17]^[18]

Based on our Medford cost data, expect the following ranges from local ADU builders. Quotes for the same scope typically vary 20-40% between contractors, so getting at least three bids is the single best way to control cost.

New Detached ADU (all-in)	$220,000-$400,000
Cost per Sq Ft	$275-$450
Garage Conversion	$100,000-$250,000
Prefab / Modular ADU (installed)	$250,000-$525,000
City Permit & Plan Review	$15.00 per $1,000 of estimated construction cost plus a $35.00 application fee, a $100.00 plan review fee for 1-4 family dwellings and $125.00 for a certificate of occupancy (Schedule of Building Fees effective July 28, 2009; Code Appendix A, § 10-35) — about $3,885 on a $250,000 ADU.
Impact Fees	None for a by-right ADU. 760 CMR 71.03(3)(b)(6) bars any impact fee or study not required of a single-family house in the same district. Medford's development linkage fees (§ 94-10.1.2) apply only to a "development impact project": nonresidential development of 10,000 sq ft or more, a residential structure of six or more units, a subdivision creating six or more units or lots, or a project of 5,000 sq ft or more that needs a density bonus, variance, special permit or map amendment. One ADU meets none of these.

For a full line-item breakdown, see our Medford ADU cost guide. To confirm what you're allowed to build before you hire, review the Medford ADU rules (max detached size: The smaller of 900 sq ft or half the principal dwelling's gross floor area. Medford § 94-8.2.3(4) and M.G.L. c. 40A § 1A / 760 CMR 71.02 agree on the number. Under 760 CMR 71.02, GFA counts every story of compliant ceiling height including basements and lofts but excludes crawl spaces, garages, attics and enclosed porches — so a 1,400 sq ft house gets a 700 sq ft unit. § 94-8.2.3(4) lets the Board exceed 900 sq ft only for a carriage house or barn with preservation value, by special permit.; owner-occupancy: Not required. § 94-8.2.3(2) still demands an affidavit that one of the two units is owner-occupied, and § 94-8.2.3(8) expires the permit every five years without a fresh affidavit; the Building Department's ADU handout (September 7, 2022, still posted) repeats both. State law overrides them: M.G.L. c. 40A § 3 bars owner-occupancy requirements, 760 CMR 71.03(2)(a) lists them first among Prohibited Regulations, and 71.03(4) bars enforcing such a condition even if imposed before January 31, 2025.).

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How to Vet an ADU Builder in Medford

License: Confirm a current contractor's license in Massachusetts and that it's in good standing. Ask for the license number and verify it with the state board.
ADU-specific experience: Ask how many ADUs they've completed in or near Medford and request addresses or photos. ADU permitting and setbacks differ from a kitchen remodel.
Portfolio & references: Get references from recent ADU clients and, if possible, visit a finished unit.
Insurance: Verify general liability and workers' compensation coverage. Ask for a certificate of insurance.
Written, detailed bid: Insist on an itemized, fixed-price or clearly-scoped bid — not a verbal estimate. It should state whether permits ($15.00 per $1,000 of estimated construction cost plus a $35.00 application fee, a $100.00 plan review fee for 1-4 family dwellings and $125.00 for a certificate of occupancy (Schedule of Building Fees effective July 28, 2009; Code Appendix A, § 10-35) — about $3,885 on a $250,000 ADU.), plan check (Standard building plan review ($100.00 plan review fee, 1-4 family dwellings). Two Massachusetts items to settle early: Title 5 — if the lot is on septic, 310 CMR 15.000 applies through the Board of Health and the § 94-8.2.3(1) plot plan must show the system; and utilities — 760 CMR 71.03(3)(b)(3) says the city may not require a separate water, sewer or electric connection, though the utility or a state board still can. Work started without a permit is charged a quadruple fee (Appendix A, § 10-35(10)). Every ADU must be assigned an address to the MassGIS standard and reported to MassGIS and EOHLC (760 CMR 71.03(8)).), and impact fees (None for a by-right ADU. 760 CMR 71.03(3)(b)(6) bars any impact fee or study not required of a single-family house in the same district. Medford's development linkage fees (§ 94-10.1.2) apply only to a "development impact project": nonresidential development of 10,000 sq ft or more, a residential structure of six or more units, a subdivision creating six or more units or lots, or a project of 5,000 sq ft or more that needs a density bonus, variance, special permit or map amendment. One ADU meets none of these.) are included.
Permit handling: Confirm they manage Medford's permit process ("Building permit, filed online through the Citizenserve portal linked from the Building Department page (building, plumbing and gas, electrical and sheet-metal permits are all filed there; no work may start until the permit card is issued). No special permit and no hearing for one ADU: § 94-8.2.2 still reads "as of right in an existing principal dwelling or by special permit from the community development board (the SPGA) in an existing detached structure," but M.G.L. c. 40A § 3 forbids a special permit or other discretionary approval for a single ADU and 760 CMR 71.03(2)(e) bars requiring the unit to be attached or detached. Expect to file the § 94-8.2.3(1) plot plan (building, proposed unit, any septic system and parking; a mortgage inspection survey suffices). Zoning questions must go to the Building Commissioner in writing; Appendix A of the Code lists a $50 fee for a review or letter of legal zoning status. Building/Zoning Department, City Hall Room 115A, (781) 393-2509; Planning, Development & Sustainability, Room 308, (781) 393-2480, ocd@medford-ma.gov.", typically The Building Department's FAQ says the building official has 30 days to review and act on a building permit application and that most reviews finish sooner; new buildings go to the weekly Tuesday development meeting for multi-department sign-off. No ADU-specific timeline is published.) and who is responsible if revisions are required.
Payment schedule: Avoid large upfront payments. A reasonable schedule ties payments to completed milestones.

Questions to Ask Before You Hire

How many ADUs have you built in Medford in the last two years?
Is your bid fixed-price, and what would trigger a change order?
Are permits, plan check, and utility connection fees included?
What's a realistic timeline, including permit review (The Building Department's FAQ says the building official has 30 days to review and act on a building permit application and that most reviews finish sooner; new buildings go to the weekly Tuesday development meeting for multi-department sign-off. No ADU-specific timeline is published.) and construction?
Who is my point of contact and how are delays communicated?
What warranty do you provide on workmanship?
Can you share three recent Massachusetts ADU client references?

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Frequently Asked Questions

How much do ADU builders charge in Medford?

ADU builders in Medford typically quote $220,000-$400,000 for a new detached unit, or about $275-$450 per square foot, including design, permitting, and construction. A garage conversion runs $100,000-$250,000 and a prefab/modular ADU averages $250,000-$525,000. Add city permit and plan-review fees ($15.00 per $1,000 of estimated construction cost plus a $35.00 application fee, a $100.00 plan review fee for 1-4 family dwellings and $125.00 for a certificate of occupancy (Schedule of Building Fees effective July 28, 2009; Code Appendix A, § 10-35) — about $3,885 on a $250,000 ADU.) plus impact fees of None for a by-right ADU. 760 CMR 71.03(3)(b)(6) bars any impact fee or study not required of a single-family house in the same district. Medford's development linkage fees (§ 94-10.1.2) apply only to a "development impact project": nonresidential development of 10,000 sq ft or more, a residential structure of six or more units, a subdivision creating six or more units or lots, or a project of 5,000 sq ft or more that needs a density bonus, variance, special permit or map amendment. One ADU meets none of these.. Quotes for the same scope commonly vary 20-40% between builders, so collect at least three bids.

How do I find a good ADU builder in Medford?

Look for a licensed contractor with completed ADU projects in Medford specifically — ADUs involve local zoning, setback rules, and utility connections that general remodelers may not have handled. Verify the license, ask for an ADU-specific portfolio and references, confirm they carry liability and workers' comp insurance, and get a written fixed-price or detailed bid. Submit a request below and we'll forward it to local ADU builders serving Medford for free quotes.

Do ADU builders in Medford handle permits?

Most full-service ADU builders manage the permit process for you. In Medford the approval process is "Building permit, filed online through the Citizenserve portal linked from the Building Department page (building, plumbing and gas, electrical and sheet-metal permits are all filed there; no work may start until the permit card is issued). No special permit and no hearing for one ADU: § 94-8.2.2 still reads "as of right in an existing principal dwelling or by special permit from the community development board (the SPGA) in an existing detached structure," but M.G.L. c. 40A § 3 forbids a special permit or other discretionary approval for a single ADU and 760 CMR 71.03(2)(e) bars requiring the unit to be attached or detached. Expect to file the § 94-8.2.3(1) plot plan (building, proposed unit, any septic system and parking; a mortgage inspection survey suffices). Zoning questions must go to the Building Commissioner in writing; Appendix A of the Code lists a $50 fee for a review or letter of legal zoning status. Building/Zoning Department, City Hall Room 115A, (781) 393-2509; Planning, Development & Sustainability, Room 308, (781) 393-2480, ocd@medford-ma.gov." with a typical review timeline of The Building Department's FAQ says the building official has 30 days to review and act on a building permit application and that most reviews finish sooner; new buildings go to the weekly Tuesday development meeting for multi-department sign-off. No ADU-specific timeline is published.. Confirm in writing whether permit fees, plan check (Standard building plan review ($100.00 plan review fee, 1-4 family dwellings). Two Massachusetts items to settle early: Title 5 — if the lot is on septic, 310 CMR 15.000 applies through the Board of Health and the § 94-8.2.3(1) plot plan must show the system; and utilities — 760 CMR 71.03(3)(b)(3) says the city may not require a separate water, sewer or electric connection, though the utility or a state board still can. Work started without a permit is charged a quadruple fee (Appendix A, § 10-35(10)). Every ADU must be assigned an address to the MassGIS standard and reported to MassGIS and EOHLC (760 CMR 71.03(8)).), and impact fees are included in the bid or billed separately.

How long does it take to build an ADU in Medford?

Plan for the permit review (The Building Department's FAQ says the building official has 30 days to review and act on a building permit application and that most reviews finish sooner; new buildings go to the weekly Tuesday development meeting for multi-department sign-off. No ADU-specific timeline is published. in Medford) plus construction. Most detached ADUs take 4-8 months of construction after permits are issued; garage conversions and prefab units are often faster. Ask each builder for a realistic schedule and what could delay it.

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Build Cost	$220,000-$400,000
Garage Conv.	$100,000-$250,000
Permit Fees	$15.00 per $1,000 of estimated construction cost plus a $35.00 application fee, a $100.00 plan review fee for 1-4 family dwellings and $125.00 for a certificate of occupancy (Schedule of Building Fees effective July 28, 2009; Code Appendix A, § 10-35) — about $3,885 on a $250,000 ADU.
Timeline	The Building Department's FAQ says the building official has 30 days to review and act on a building permit application and that most reviews finish sooner; new buildings go to the weekly Tuesday development meeting for multi-department sign-off. No ADU-specific timeline is published.
1BR Rent	$2,500-$2,800/mo

What ADU Builders Cost in Medford [16][17][18]