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 [11]
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) | $230,000-$400,000 |
| Cost per Sq Ft | $300-$500 |
| Garage Conversion | $115,000-$230,000 |
| Prefab / Modular ADU (installed) | $165,000-$330,000 |
| City Permit & Plan Review | From the city's posted Schedule of Building Fees (effective July 28, 2009 and still the version linked from the Building Department page): $15.00 per $1,000.00 of estimated construction cost, plus a $35.00 application fee; a Plan Review Fee for 1-4 family dwelling units of $100.00; and a certificate of occupancy for an existing residential building at $125.00. On a $250,000 ADU that is roughly $3,750 + $35 + $100, about $3,885, before separate plumbing and gas, electrical and sheet metal/mechanical permits, which are billed on their own schedules. Note the sting in the tail: work started without a building permit is charged a QUADRUPLE FEE |
| Impact Fees | None for a by-right ADU. Massachusetts municipalities have no general ADU impact fee power, and 760 CMR 71.03(3)(b)(6) makes unreasonable "[a]ny requirement for any impact analysis, study, report, or impact fee that is not required for the development of a Single-family Residential Dwelling" in the same district. Medford's own development linkage fees at § 94-10.1 are triggered only by a residential development of six units or more, a subdivision creating six or more units or lots, a nonresidential project of 10,000 sq ft or more, or a project of 5,000 sq ft or more that needs a density bonus, variance, special permit or map amendment — an ADU built by right meets none of those thresholds |
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 gross floor area of the principal dwelling. On this point Medford and the Commonwealth agree: "The accessory dwelling unit shall not be larger in floor area than one-half the floor area of the principal dwelling, or 900 square feet, whichever is smaller" (Medford Zoning Ordinance § 94-8.2.3(4)), and M.G.L. c. 40A § 1A defines an ADU as one that "is not larger in gross floor area than 1/2 the gross floor area of the principal dwelling or 900 square feet, whichever is smaller." Note which way that cuts: if your house is under 1,800 sq ft of gross floor area, the half-GFA rule binds long before the 900 does — a 1,400 sq ft house buys a 700 sq ft ADU. Gross floor area is measured under 760 CMR 71.02 as the sum of all stories of compliant ceiling height including basements and lofts, "but excluding crawl spaces, garage parking areas, attics, enclosed porches and similar spaces," so an unfinished attic or an attached garage does not enlarge your allowance. Medford's own text lets the Community Development Board make an exception "in the event that the detached accessory structure has some preservation value, as with a carriage house or a barn" — that is a discretionary route above 900 sq ft, not a right; owner-occupancy: Not required — and this is the single provision where Medford's published rules are most clearly wrong. Section 94-8.2.3(2) still says "[a]n affidavit shall be provided stating that one of the two dwelling units shall be occupied by the owner of the property," and § 94-8.2.3(8) makes the permit expire after five years unless the owner re-files that affidavit. Both are superseded. M.G.L. c. 40A § 3 provides that the use of land or structures for an ADU "shall not require owner occupancy of either the accessory dwelling unit or the principal dwelling," and 760 CMR 71.03(2)(a) lists an owner-occupancy requirement first among the Prohibited Regulations. 760 CMR 71.03(4) goes further and bars a municipality from enforcing such a condition even where it was imposed before January 31, 2025. The related ban on holding the ADU "in separate ownership from the principal structure/dwelling unit" in the same subsection travels with the owner-occupancy scheme — ask the Building Commissioner in writing how the city is applying it).
Get Free ADU Quotes in Medford
Tell us about your project and we'll connect you with ADU builders serving Medford. Free, no obligation — you choose who to work with.
Takes about a minute.
Up to 5 independent local ADU builders — never more, and we tell them nothing you don't submit here.
Compare quotes, verify license & insurance, hire (or don't). No spam either way.
🔒 Your info is secure. We share it only with contractors quoting your project. No spam, no obligation.
Just browsing? Search ADU builders near you by ZIP code.
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 (From the city's posted Schedule of Building Fees (effective July 28, 2009 and still the version linked from the Building Department page): $15.00 per $1,000.00 of estimated construction cost, plus a $35.00 application fee; a Plan Review Fee for 1-4 family dwelling units of $100.00; and a certificate of occupancy for an existing residential building at $125.00. On a $250,000 ADU that is roughly $3,750 + $35 + $100, about $3,885, before separate plumbing and gas, electrical and sheet metal/mechanical permits, which are billed on their own schedules. Note the sting in the tail: work started without a building permit is charged a QUADRUPLE FEE), plan check (Standard building plan review; the state building code requires three sets of plans, and Medford charges a $100.00 Plan Review Fee for 1-4 family dwelling units. Two Massachusetts-specific items to check early. First, Title 5: if the property is on a septic system rather than sewer, 310 CMR 15.000 applies and is expressly preserved by M.G.L. c. 40A § 3, and MassDEP issued Title 5 guidance for ADUs updated September 11, 2025 — the local Board of Health, not the Building Department, is the authority. Second, utilities: 760 CMR 71.03(3)(b)(3) says a municipality "may not require a separate utility connection, such as water, sewer, electric," though the utility itself, a state or regional board, or a court still can. Every ADU must also 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. Massachusetts municipalities have no general ADU impact fee power, and 760 CMR 71.03(3)(b)(6) makes unreasonable "[a]ny requirement for any impact analysis, study, report, or impact fee that is not required for the development of a Single-family Residential Dwelling" in the same district. Medford's own development linkage fees at § 94-10.1 are triggered only by a residential development of six units or more, a subdivision creating six or more units or lots, a nonresidential project of 10,000 sq ft or more, or a project of 5,000 sq ft or more that needs a density bonus, variance, special permit or map amendment — an ADU built by right meets none of those thresholds) are included.
- Permit handling: Confirm they manage Medford's permit process ("A building permit, filed online through the city's Citizenserve portal from the Building Department's permits page; three sets of plans are required by the state building code. No special permit and no public hearing are needed for one ADU, whatever the local text says. Medford's § 94-8.2.2 still reads: "Accessory dwelling units may be allowed as of right in an existing principal dwelling or by special permit from the community development board (the SPGA) in an existing detached structure on the same lot" — but M.G.L. c. 40A § 3 forbids any "special permit or other discretionary zoning approval" for a single ADU in a single-family residential zoning district, and 760 CMR 71.03(2)(e) separately bars a municipality from requiring that an ADU "be attached to or detached from the Principal Dwelling." Note also that Medford's text contemplates only conversions of existing buildings; new detached construction is not addressed at all, which is not a lawful basis for refusal. You will still need to file the § 94-8.2.3(1) plot plan showing the building on the lot, the proposed unit, any septic system and parking — a mortgage inspection survey suffices. Building/Zoning Department, City Hall Room 115A, (781) 393-2509; Planning, Development & Sustainability, Room 308, (781) 393-2480, ocd@medford-ma.gov", typically Confirm with the Medford Building Department at (781) 393-2509 — the city publishes no ADU-specific review timeline. What you can count on is that there is no hearing to wait for: because one ADU is a protected use under M.G.L. c. 40A § 3, there is no Community Development Board agenda, no abutter notice and no 20-day appeal period on a special permit, so the clock is ordinary building-permit review rather than a discretionary land-use calendar) 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 (Confirm with the Medford Building Department at (781) 393-2509 — the city publishes no ADU-specific review timeline. What you can count on is that there is no hearing to wait for: because one ADU is a protected use under M.G.L. c. 40A § 3, there is no Community Development Board agenda, no abutter notice and no 20-day appeal period on a special permit, so the clock is ordinary building-permit review rather than a discretionary land-use calendar) 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?
Finance Your ADU Project
Most ADU projects are funded through HELOCs, construction loans, or cash-out refinancing. Compare rates from top lenders.
Some links on this page are affiliate links. We may earn a commission at no extra cost to you. Learn more
Are you an ADU builder? Get Medford leads
Homeowners on this page submit real ADU project requests in Medford. Each one goes to up to five local builders — that is what the homeowner agrees to — so claiming never takes it from anyone and there is no bidding. In practice far fewer ever make contact, which is why the number is five rather than three. A flat $50 only on the leads you accept: no subscription, no contract, and you deal with the homeowner directly.
Get Medford ADU Leads →Frequently Asked Questions
How much do ADU builders charge in Medford?
How do I find a good ADU builder in Medford?
Do ADU builders in Medford handle permits?
How long does it take to build an ADU in Medford?
Get Free ADU Builder Quotes in Medford
Compare bids from experienced local Medford ADU builders. Free, no obligation.
Get Free Quotes →