How Much Does an ADU Cost in Medford, MA?

Construction Cost Breakdown

Building an ADU in Medford costs between $230,000-$400,000 for new construction, with per-square-foot costs averaging $300-$500. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $115,000-$230,000, while prefab/modular ADUs fall in between at $165,000-$330,000.

Permit Costs & Timeline

Permit fees in Medford are 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. The review timeline is 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, with 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)). Impact fees are 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. Pre-approved plans: None from the City of Medford — no city plan gallery appears on the Building Department or Planning pages as of September 1, 2026. The Commonwealth fills the gap: EOHLC's Accessory Dwelling Units page hosts a free, searchable library of downloadable ADU designs alongside financing and technical-assistance programmes. Start there before you commission a custom set.

Rental Income & ROI

A typical ADU in Medford generates approximately $28,200 per year in rental income based on average 1-bedroom rents. At an average construction cost of $315,000, the estimated payback period is 11.2 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in Medford and varies by market (often less than build cost).

Ways to Reduce ADU Costs in Medford