Yes: since Ordinance No. 36552 (third and final reading April 28, 2025) one accessory dwelling unit is permitted by right on a single-family lot in Waltham's RA-1 through RD, HR1, BA and BB districts, with no special permit, no hearing and no owner-occupancy rule (Waltham Zoning Code § 3.23). The unit must be between 450 sq ft and the smaller of 900 sq ft or half the principal dwelling's gross floor area, and it takes a building permit with plans showing dimensional compliance, parking and square footage (§ 3.23(b), (h)). One off-street space is required unless the lot is within half a mile of a transit station, which the city's ADU form lets you prove with a MapGeo radius map (§ 3.23(d)). Section 3.23(c) sends an ADU to the district's own setbacks (40 ft front and rear in RA-1), but 760 CMR 71.03(3)(b)(2) entitles a protected-use ADU to the more permissive accessory-building standard of 5 ft at the side and rear (§ 4.221), so raise it with the Building Department before you site a detached unit. No amendment to § 3.23 appears in the City Council's 2026 dockets, and the residential building permit fee is $12 per $1,000 of construction cost.
Zoning & Size Requirements [1][2][3][4][5][6][7][8]
Yes — Waltham allows ADUs. A detached ADU can typically be up to 900 sq ft under current Massachusetts and Waltham zoning rules.
See what this means for your lot — ask Waltham ADU builders for a quote →
| Allowed Zones | Permitted by right (Y) in RA-1, RA-2, RA-3, RA-4, RB, RC, RD, HR1, BA and BB; not permitted (N) in HR2, BC, LC, C, I and CR (§ 3.4 Table of Uses row for Accessory Dwelling Units as replaced by Ordinance No. 36552; use reference §§ 3.23 and 3.616). The HR2 'N' looks preempted: Table 4.11 carries an HR1 & HR2 single-family detached row, and 760 CMR 71.02 protects any district where single-family dwellings are permitted. Ask the Building Department before accepting a refusal in HR2. |
| Max Size (Detached) | 450 to 900 sq ft: 'The minimum floor area of an ADU shall not be less than 450-square feet. The maximum floor area of an ADU shall not exceed 900-square feet, or 50% of the total gross floor area of the principal dwelling unit, whichever is smaller' (§ 3.23(b), Ord. No. 36552). Under 1,800 sq ft of house the half rule binds first; gross floor area follows 760 CMR 71.02. The 450 sq ft floor is Waltham's own; 760 CMR 71.02 allows 'additional size restrictions' subject to the 71.03(3)(a) test. |
| Max Size (Attached) | The same rule for every type: not less than 450 sq ft and not more than the smaller of 900 sq ft or 50 percent of the principal dwelling's total gross floor area (§ 3.23(b)). The city's ADU application form recognises four types (attached, detached, internal and secondary) and applies one size rule to all; only a 'secondary' (second) ADU needs a City Council special permit under § 3.616. |
| Max Size (JADU) | Not a category in Massachusetts. Neither M.G.L. c. 40A, 760 CMR 71.00 nor the Waltham Zoning Code recognises a junior ADU. A unit carved out of the house is an 'internal' ADU on Waltham's form and takes the ordinary 450-900 sq ft rule. |
| Max Height | The district maximum under § 3.23(c): 35 ft and 2½ stories in RA-1 through RA-4, 40 ft and 3 stories in RB and RC, 50 ft and 4 stories in RD, 74 ft and 6 stories in HR1 (Table 4.11, Supp. No. 14). Waltham's accessory-building rule is tighter (one story; above 15 ft no more than 125% of the least horizontal dimension, 20 ft maximum; § 4.223), but 760 CMR 71.03(3)(b)(2) entitles a protected-use ADU to whichever standard is more permissive. Expect to argue it for a two-storey detached unit. |
| Max Units | One by right; a second needs a City Council special permit: 'A single ADU, accessory to a principal dwelling unit, is permitted by-right. The locating of more than one ADU on a single lot shall require a special permit from the City Council, consistent with Section 3.616' (§ 3.23(i); 760 CMR 71.03(5)). Under § 3.616 a secondary ADU must meet § 3.23, fit the house and neighbourhood, have its own space unless near transit, and be sprinklered where four or more units share a structure. |
Setback Requirements [1][2][3][4][5][6][7][8]
Waltham requires a rear setback of about 5 ft for a detached ADU, and one off-street parking space is required. Owner-occupancy is not required — you can rent it out without living on the property.
| Rear Setback | 5 ft from the rear lot line is the operative figure for a protected-use ADU: the accessory-building standard is 5 ft from rear and side lines and 10 ft from the house (§ 4.221), and 760 CMR 71.03(3)(b)(2) bars any ADU setback stricter than the principal-dwelling or accessory-structure standard, 'whichever results in more permissive regulation'. On its face § 3.23(c) applies the district rear yard — 40 ft in RA-1/RA-2, 30 ft in RA-3/RA-4/RB, 20 ft in RC/HR1, 60 ft in RD (Table 4.11). The 10-ft separation and 25%-of-rear-yard cap still apply. |
| Side Setback | 5 ft from the side lot lines under the accessory-building standard (§ 4.221 and the accessory-building row of Table 4.11), which 760 CMR 71.03(3)(b)(2) entitles a protected-use ADU to claim. On its face § 3.23(c) applies the district side yard — 20 ft in RA-1 and RA-2, 15 ft in RA-3 and RA-4, 10 ft in RB, RC and HR1, 45 ft in RD (Table 4.11). |
| Front Setback | The district front yard, with no accessory-structure relief: 40 ft in RA-1 and RA-2, 25 ft in RA-3 and RA-4, 15 ft in RB, 10 ft in RC, 75 ft in RD, 10 ft in HR1 (25 ft on the HR1 & HR2 single-family detached row) (Table 4.11, Supp. No. 14). The accessory-building row of Table 4.11 gives the front setback as 'As required by district', so unlike the side and rear yards there is nothing more permissive to claim. Plan a detached ADU for the rear of the lot. |
| Parking Required | One off-street space, or none near transit: 'at least one off-street parking space in addition to the parking required for the principal dwelling unit, unless the lot on which the ADU is located is within 0.5 miles from a Transit Station, as defined by 760 CMR 71.00' (§ 3.23(d)). The ADU form has a tick box for a lot 'within 0.5 miles / 2,640ft from a Transit Station' and asks for a MapGeo radius map. 760 CMR 71.02 counts any Transit Authority bus stop as a Bus Station. One space is the ceiling. |
| Owner Occupancy | Not required. Ordinance No. 36552 struck the former § 3.23 'in its entirety'; the replacement has no owner-occupancy condition, covenant or re-certification, and the old Board of Appeals special-permit route (S2 in the 2017 Table of Uses) is gone. State law bars it anyway: M.G.L. c. 40A § 3 as amended by St. 2024 c. 150 and 760 CMR 71.03(2)(a) make owner occupancy a Prohibited Regulation, and 71.03(4) stops the city enforcing such a condition even on an ADU approved before January 31, 2025. |
| Min Lot Size | None for the ADU: 'a Municipality may not require a minimum Lot size for a Protected Use ADU' (760 CMR 71.03(3)(b)(2)), and § 3.23 sets none. District lot minimums (sq ft / frontage ft) remain: RA-1 20,000/100, RA-2 15,000/80, RA-3 9,600/70, RA-4 7,000/60, RB single-family 6,000/60, RC 6,000/50, RD 5 acres, HR1 10,000/50 (Table 4.11). Maximum lot coverage is 20% in RA-1 and RA-2, 25% in RA-3 and RA-4, 30% in RB, RC and RD; footnote (2) counts 'all principal and accessory buildings'. |
Permit Process & Fees [9][10][11][12][13]
An ADU permit in Waltham goes through a standard permit review. Review time: not published: the Building Department gives no ADU review time, so confirm at 781-314-3275. Since April 2025 there is no Zoning Board hearing, abutter period or appeal window; the surveyor's as-built and the fire-department plan stamp on the checklist are the usual long-lead items. Permit fees: Residential building permits are $12 per $1,000 of estimated construction cost, $50 minimum (about $3,000 on a $250,000 ADU); plumbing is $25 for the first fixture and $10 each after, gas $30 plus $15 per added appliance, and a residential trench permit $50 (Building Department, Sept. 2026).
| Approval Process | A building permit only: no special permit, hearing or covenant for a single ADU. 'A building permit is required for the construction or conversion of an ADU. The building permit application shall include detailed plans that demonstrate compliance with this chapter, including dimensional compliance, parking requirements, and the total square footage of the ADU' (§ 3.23(h)). The Building Department's ADU Application Package pairs a property-information form (zoning district, existing units, total gross floor area including basement and habitable attics, parking, ADU type and size, parking box or transit radius map, residential-use certification) with an ADU checklist: floor plans of the whole structure with the basement's gross floor area, an as-built from a professional land surveyor for an attached or detached unit, zoning district and ward, unit size, parking per 760 CMR 71.00, water and sewer per the Engineering guidelines, and dimensional compliance with the district. The general permit checklist adds the owner-signed application with the CSL and HIC holder (the same person), workers' compensation affidavit and insurance certificate, waste debris form, certified abutter letters for a new structure or addition, fire-department-stamped plans with the smoke and CO layout, a certified plot plan for new construction, a HERS rating, sheet metal form, habitable-space form for a basement, Engineering I&I sign-off, and the whole package on a thumb drive. Applications filed after July 1, 2025 must meet the 10th Edition of the state building code. Building Department, Government Center, 119 School Street, Room 25: 781-314-3275 (Sandra Vidal, 781-314-3284, for a walk-through). Planning Department, 25 Lexington Street, 2nd Floor: 781-314-3370. |
| Review Timeline | Not published: the Building Department gives no ADU review time, so confirm at 781-314-3275. Since April 2025 there is no Zoning Board hearing, abutter period or appeal window; the surveyor's as-built and the fire-department plan stamp on the checklist are the usual long-lead items. |
| Permit Fees | Residential building permits are $12 per $1,000 of estimated construction cost, $50 minimum (about $3,000 on a $250,000 ADU); plumbing is $25 for the first fixture and $10 each after, gas $30 plus $15 per added appliance, and a residential trench permit $50 (Building Department, Sept. 2026). |
| Impact Fees | None. Waltham's ADU ordinance imposes none, and 760 CMR 71.03(3)(b)(6) makes unreasonable '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. Only the valuation-based building permit fee and the trade permits apply. |
| Plan Check | Building plan review against the 10th Edition of the Massachusetts State Building Code (mandatory for applications filed after July 1, 2025) plus a zoning check against § 3.23 and the district's Table 4.11 figures. Utilities: § 3.23(f) requires connection to public water and sewer or Title 5 compliance under 310 CMR 15.000, and the checklist routes water and sewer through the Engineering guidelines; 760 CMR 71.03(3)(b)(3) says the city itself may not require a separate utility connection, though a utility, a state or regional board or a court can. Egress: § 3.23(g) requires a separate entrance, directly from outside or through a shared entry hall or corridor, sufficient for safe egress under the building code, the same wording as 760 CMR 71.02. Every ADU must be assigned an address to the MassGIS standard and reported to MassGIS and EOHLC (71.03(8)). |
| Pre-Approved Plans | None from the City of Waltham. As of September 20, 2026 the Building Department's ADU links are the Application Package and the ordinance; the package assumes custom plans and a surveyor's as-built. The state housing office (EOHLC) publishes ADU resources on mass.gov, including a design library; that page could not be re-read for this update, so check it directly and confirm with the Building Department (781-314-3275) that a state design can be adapted to your lot. |
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Construction Costs [14][15][16]
Building an ADU in Waltham typically costs $200,000-$400,000 ($275-$450 per sq ft); a garage conversion runs $100,000-$250,000.
See what this means for your lot — ask Waltham ADU builders for a quote →
| Average Build Cost | $200,000-$400,000 |
| Cost per Sq Ft | $275-$450 |
| Garage Conversion | $100,000-$250,000 |
| Prefab ADU (Installed) | $250,000-$525,000 |
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Rental Income Potential [17][18]
A 2-bedroom ADU in Waltham rents for around $3,050-$3,640/mo, an estimated 5-8% annual return.
| Avg Rent (1 Bedroom) | $2,550-$3,050/mo |
| Avg Rent (2 Bedroom) | $3,050-$3,640/mo |
| Short-Term Rental | No. § 3.23(e) bars short-term rentals of an ADU (any room or the unit let under 31 consecutive days) and customary home occupations; M.G.L. c. 40A § 3 and 760 CMR 71.03(3)(c) allow the STR ban. Long-term letting is fine. |
| Est. Annual ROI | 5-8% annual return |
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Recent Law Changes
What's Changed Recently
- The Affordable Homes Act, St. 2024, c. 150 §§ 7-8, effective February 2, 2025, amended M.G.L. c. 40A §§ 1A and 3 so that no zoning ordinance may prohibit, unreasonably restrict or require a special permit for a single ADU in a single-family residential zoning district; owner occupancy may not be required, no more than one parking space may be required, and none within half a mile of a transit station
- EOHLC's 760 CMR 71.00, Protected Use Accessory Dwelling Units, took effect January 31, 2025 (Mass. Register Issue 1540): it lists the Prohibited Regulations (71.03(2)), the Unreasonable Regulation test and dimensional floor (71.03(3)), and bars enforcement of such conditions even on ADUs approved before that date (71.03(4)). Read on LII on September 20, 2026; no later amendment appears
- Waltham Ordinance No. 36552 (first reading March 24, second April 14, third and final April 28, 2025) added the § 2.302A definition, struck and replaced § 3.23, replaced the § 3.4 Table of Uses row so that ADUs are permitted by right (Y) in RA-1 through RD, HR1, BA and BB, and rewrote § 3.616 to govern only special permits for more than one ADU on a lot
- What the ordinance repealed: the Board of Appeals special permit (S2) that the 2017 Table of Uses still shows for accessory dwelling units in the Residence A districts, and every condition that came with it. The replacement § 3.23 carries no owner-occupancy, lot-size or re-certification requirement
- Waltham's 450 sq ft minimum floor area is the one place its rules are stricter than the state floor. 760 CMR 71.02 allows a municipality to impose 'additional size restrictions', so the minimum is not automatically void, but it is testable under the 71.03(3)(a) reasonableness standard and its application to a smaller conversion has not been decided
- No ADU amendment in 2026: the City Council's dockets and Ordinances & Rules Committee agendas from January 12 to September 14, 2026 carry the inclusionary Affordable Housing amendment, a Pet Grooming use, a 495 Lincoln Street map change and the RCI/MIRROD overlay districts, none of which touches § 3.23. The Building Department still links Ordinance No. 36552 as its 'Accessory Dwelling Unit Regulations'
- Stale mirrors to ignore: the Building Department's 'Table of Uses' PDF is Supplement No. 15, current only through Ordinance No. 33817 of August 1, 2017, and still shows the repealed S2 row; and the online Zoning Code on eCode360 (code WA1697), at its last readable snapshot of July 30, 2025, included legislation only through December 26, 2023 with Orders 36462 and 36463 pending and no sign of 36552. The city's own PDF of the ordinance governs
- Sources for this update (September 20, 2026): the city's PDFs of Ordinance No. 36552, the ADU Application Package, the § 4.11 Table of Dimensional Regulations (Supp. No. 14) and § 4.12 footnotes, the Building Department fee pages, and 760 CMR 71.02-71.03 on LII. eCode360 could not be read (bot wall) and mass.gov was unreachable, so those pages were not re-read
Tips for Building an ADU in Waltham
- Ignore the Table of Uses PDF on the Building Department page. It is a 2017 scan (Supp. No. 15) that still shows an ADU needing a Board of Appeals special permit. The governing document is Ordinance No. 36552, linked from the same page as 'Accessory Dwelling Unit Regulations'
- Design to 450 sq ft or more. Waltham will not permit an ADU under 450 sq ft, which rules out the compact basement or over-garage conversions that pass elsewhere in Massachusetts; if your conversion is smaller, ask the Building Department how the minimum is being applied before you pay for drawings
- Ask for the accessory-structure setbacks in writing. Section 3.23(c) points at the district table (40 ft rear in RA-1), but 760 CMR 71.03(3)(b)(2) entitles a protected-use ADU to the more permissive standard, and Waltham's own accessory-building rule is 5 ft at the side and rear (§ 4.221). Keep 10 ft from the house and inside 25% of the required rear yard
- Get the transit radius map early. The ADU form waives the parking space if you attach a MapGeo map showing the lot within 2,640 ft of a transit station, and 760 CMR 71.02 counts any MBTA bus stop as a Bus Station, not only the commuter rail platforms
- If you hold an old Waltham ADU special permit with an owner-occupancy or re-certification condition, 760 CMR 71.03(4) says the city may not enforce it, whether the condition was imposed before or after January 31, 2025
- Book the surveyor first. The ADU checklist requires an as-built from a professional land surveyor for any attached or detached unit, and a certified plot plan for a new structure; these and the fire-department plan stamp are the long-lead items
- Budget the trades separately: $12 per $1,000 covers the building permit only; plumbing ($25 first fixture, $10 each after), gas ($30 first appliance, $15 each after) and electrical (Wires Department, 781-314-3175) are separate permits, and a utility trench in the street is a $50 residential trench permit
- In HR2 the use table says N, but Table 4.11 carries an HR1 & HR2 single-family detached row, which makes HR2 a Single-family Residential Zoning District under 760 CMR 71.02 and brings the c. 40A § 3 protection with it. Put the argument in writing to the Inspector of Buildings rather than abandoning the project
- Cost basis: statewide 2026 industry guides, not Waltham data. Dwelly (March 2026) puts stick-built ADUs at $275-$450 per sq ft (600 sq ft $165,000-$270,000; 800 sq ft $220,000-$360,000; most projects $200,000-$400,000); Horizon ADU (July 2026) gives a detached 900 sq ft cottage at $250,000-$360,000 and a basement or garage conversion at $100,000-$250,000; ADU Wizard (2026) prices installed prefab units of 650-900 sq ft in Greater Boston at $250,000-$525,000. Rents are HUD FY2027 Small Area FMRs for Waltham ZIPs 02451-02454 (1BR $2,550-$3,050; 2BR $3,050-$3,640). Get three local bids
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Sources & References
All data on this page is sourced from official government records and verified market data. View our full methodology.
- Waltham Ordinance No. 36552, amending Art. II § 2.302 (adding § 2.302A), Art. III § 3.23, the § 3.4 Table of Uses and § 3.616 of the Zoning Code to regulate accessory dwelling units (third and final reading April 28, 2025), City of Waltham PDF Municipal Code — Accessed 2026-09-20
- Waltham Zoning Code § 4.11, Table of Dimensional Regulations (Z Attachment 5, Supp. No. 14; amended through Ord. No. 31971 of 6-24-2013), scanned PDF read by OCR Municipal Code — Accessed 2026-09-20
- Waltham Zoning Code § 4.12, Footnotes to the Table of Dimensional Requirements (footnotes (1)-(3)), and Art. IV §§ 4.221-4.223 accessory-building location, area and height (in the ADU Application Package) Municipal Code — Accessed 2026-09-20
- Waltham Zoning Code § 3.4, Table of Uses (Z Attachment 4, Supp. No. 15, current only through Ord. No. 33817 of 8-1-2017): legend Y/N/S1/S2/Y1 and the superseded S2 row for accessory dwelling units Municipal Code — Accessed 2026-09-20
- 760 CMR 71.02, Definitions: Accessory Dwelling Unit (incl. 'additional size restrictions'), Bus Station, Commuter Rail Station, Transit Station, Gross Floor Area, Protected Use ADU, Single-family Residential Zoning District (eff. 1/31/2025) state_statute — Accessed 2026-09-20
- 760 CMR 71.03, Regulation of Protected Use ADUs: (2) Prohibited Regulations, (3)(b)(2) dimensional standards and no minimum lot size, (3)(b)(3) utilities, (3)(b)(6) impact fees, (3)(c) short-term rentals, (4) pre-existing conditions, (5) special permit for additional ADUs, (8) addresses state_statute — Accessed 2026-09-20
- ADU Law: Acts of 2024, Chapter 150, Sections 7 and 8 (amendments to M.G.L. c. 40A §§ 1A and 3), EOHLC (mass.gov unreachable on 9/19-9/20/2026; not re-read) state_statute — Accessed 2026-09-01
- Waltham City Council Agenda Center: 2026 City Council dockets (Jan 12 - Sep 14, 2026) and Ordinances & Rules Committee agendas, checked for ADU / § 3.23 items (none) Municipal Code — Accessed 2026-09-20
- City of Waltham ADU Application Package: ADU property-information form, ADU check list, Ordinance No. 36552 and Zoning Code § 4.22 accessory-building provisions (Building Department) Planning Department — Accessed 2026-09-20
- Building Department, City of Waltham: permit requirements, residential fee $12 per $1,000 ($50 minimum), commercial $22 per $1,000, 10th Edition code from July 1, 2025, staff contacts Planning Department — Accessed 2026-09-20
- Plumbing and Gas Fees, City of Waltham Building Department (residential plumbing $25 first fixture / $10 each additional; gas $30 / $15) Planning Department — Accessed 2026-09-20
- Trench Permit Fee Schedule, City of Waltham Building Department (residential single $50, residential multi $100 max) Planning Department — Accessed 2026-09-20
- Accessory Dwelling Units, EOHLC (state ADU resources; mass.gov unreachable on 9/19-9/20/2026, not re-read) Government Data — Accessed 2026-09-01
- Dwelly, How Much Does an ADU Cost in Massachusetts in 2026? (Mar 7, 2026) industry — Accessed 2026-09-20
- Horizon ADU, How Much Does a 900 Sq Ft ADU Cost in Massachusetts? (Jul 24, 2026) industry — Accessed 2026-09-20
- ADU Wizard, How Much Does an ADU Cost in Massachusetts in 2026? industry — Accessed 2026-09-20
- HUD FY2027 Small Area Fair Market Rent Schedule, Boston-Cambridge-Quincy, MA-NH HUD Metro FMR Area, ZIPs 02451, 02452, 02453, 02454 Government Data — Accessed 2026-09-20
- HUD Fair Market Rents (FY2027 documentation system) Government Data — Accessed 2026-09-20
- Planning Department, City of Waltham, 25 Lexington Street 2nd Floor, 781-314-3370 (zoning administration is by the Building Department) Planning Department — Accessed 2026-09-20
- U.S. Census Bureau, 2020 Decennial Census, Waltham city, Massachusetts (65,218) Government Data — Accessed 2026-09-01
Frequently Asked Questions
Can I build an ADU in Waltham?
Yes. ADUs are allowed in Permitted by right (Y) in RA-1, RA-2, RA-3, RA-4, RB, RC, RD, HR1, BA and BB; not permitted (N) in HR2, BC, LC, C, I and CR (§ 3.4 Table of Uses row for Accessory Dwelling Units as replaced by Ordinance No. 36552; use reference §§ 3.23 and 3.616). The HR2 'N' looks preempted: Table 4.11 carries an HR1 & HR2 single-family detached row, and 760 CMR 71.02 protects any district where single-family dwellings are permitted. Ask the Building Department before accepting a refusal in HR2. in Waltham. The maximum size for a detached ADU is 450 to 900 sq ft: 'The minimum floor area of an ADU shall not be less than 450-square feet. The maximum floor area of an ADU shall not exceed 900-square feet, or 50% of the total gross floor area of the principal dwelling unit, whichever is smaller' (§ 3.23(b), Ord. No. 36552). Under 1,800 sq ft of house the half rule binds first; gross floor area follows 760 CMR 71.02. The 450 sq ft floor is Waltham's own; 760 CMR 71.02 allows 'additional size restrictions' subject to the 71.03(3)(a) test.. Owner-occupancy is not required, so you can rent out the ADU.
How much does an ADU cost in Waltham?
ADU construction in Waltham typically costs $200,000-$400,000. Garage conversions run $100,000-$250,000, and prefab ADUs cost $250,000-$525,000.
How much can I rent an ADU for in Waltham?
Average ADU rents in Waltham are $2,550-$3,050/mo for a 1-bedroom and $3,050-$3,640/mo for a 2-bedroom unit.
Do I need parking for an ADU in Waltham?
One off-street space, or none near transit: 'at least one off-street parking space in addition to the parking required for the principal dwelling unit, unless the lot on which the ADU is located is within 0.5 miles from a Transit Station, as defined by 760 CMR 71.00' (§ 3.23(d)). The ADU form has a tick box for a lot 'within 0.5 miles / 2,640ft from a Transit Station' and asks for a MapGeo radius map. 760 CMR 71.02 counts any Transit Authority bus stop as a Bus Station. One space is the ceiling.. Check with Waltham planning department for the latest Massachusetts ADU parking rules, as many states have relaxed requirements in recent years.
How long does it take to get an ADU permit in Waltham?
Waltham does not publish a standard ADU review timeline. the Building Department gives no ADU review time, so confirm at 781-314-3275. Since April 2025 there is no Zoning Board hearing, abutter period or appeal window; the surveyor's as-built and the fire-department plan stamp on the checklist are the usual long-lead items. Permit fees: Residential building permits are $12 per $1,000 of estimated construction cost, $50 minimum (about $3,000 on a $250,000 ADU); plumbing is $25 for the first fixture and $10 each after, gas $30 plus $15 per added appliance, and a residential trench permit $50 (Building Department, Sept. 2026).
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