Tewksbury never adopted an ADU bylaw, so the state law applies to your lot directly. One ADU as of right, capped at 900 square feet or half your house — whichever is smaller. The old Family Suite bylaw is still on the books, and most of it can no longer be enforced against you.
No ADU zoning amendment has been adopted here — confirmed across three consecutive town meetings: the Annual in May 2025, the Special in October 2025, and the Annual in May 2026. None carried an ADU article.
That is not a problem. Where a town is silent, the state law controls directly, and the town has been administering ADUs under it since an ADU FAQ session in August 2025 run by the Town Planner and Building Commissioner.
Your cap is the state figure: 900 square feet or half the principal dwelling’s gross floor area, whichever is smaller. Read that carefully — 900 is a ceiling, not an allowance. On a 1,500 sq ft house the cap is 750 sq ft. The 900 figure only governs once the principal dwelling passes roughly 1,800 sq ft.
Tewksbury’s legacy Family Suite bylaw survives in the zoning code. It carries a family-relationship requirement, owner-occupancy, an attachment requirement, no separate entrance, annual certification, and a Planning Board special permit.
Every one of those conditions is preempted for a protected ADU. The town cannot impose them on you. Filing on the Family Suite application concedes a requirement the town has no authority to enforce — file for a plain building permit instead.
There is one genuine reason to consider the old route. A Family Suite may run to 1,000 square feet with up to two bedrooms — larger than the protected cap. The price is a Planning Board special permit, attachment to the main house, a relative in occupancy, and annual notarised certification. On a large house where half the floor area already exceeds 900, the protected route is better. On a smaller house where the half-GFA test bites, the comparison is worth running.
Tewksbury is the most sewered of the three Middlesex towns we cover. The town runs a municipal system and states that the majority of its build-out was complete as of November 2009.
The town’s own ADU guidance notes that DPW permits may be required if the ADU exceeds existing septic capacity, which would force a sewer connection. Water is municipal, with a treatment plant rated to 7 million gallons a day.
Stretch Code, adopted by voice vote at the May 2011 Town Meeting and effective 1 January 2012. Historic homes were exempted. The Specialized Code has not been adopted.
Practically, budget for a HERS rater on the job targeting 52–58 — your existing house is excluded from the ADU’s rating. Expect one 50-amp 240V branch circuit per dwelling unit within six feet of a parking space, marked EV READY. A new detached unit with 600 sq ft or more of roof oriented between 110 and 270 degrees also needs a solar-ready zone of at least 300 sq ft, with a capped penetration sleeve, documented structural loads, reserved breaker space and a permanent certificate near the panel.
Residential building permits run a $30 minimum plus $10 per $1,000 of valuation, which includes a $10 GIS fee. Electrical for a new single-family service and wiring is $100 under 200 amps, $150 at 200 amps and above. Plumbing is $30 minimum up to two fixtures, $10 each additional; gas is the same. Sheet metal $10 per $1,000, $30 minimum. Residential certificate of occupancy $25.
Inspections need 24 hours’ notice, and building inspections run weekdays between 10am and 1pm.
We would rather show you the gap than fill it with a guess. Confirm anything below with the town before you rely on it.
The dimensional table — setbacks, lot coverage, height — is the largest single gap here, and we will not guess at a setback. Whether site plan review is triggered. What percentage of the town is sewered and which neighbourhoods remain on septic, plus the sewer connection and betterment fee schedule. Water connection fees. Whether the Board of Health has septic rules stricter than Title 5. Whether a historic district or demolition delay bylaw exists.
One item worth raising with the Building Commissioner directly: the town has given verbal ADU guidance of a two-hour fire-rated separation for an attached unit, which is stricter than the residential code baseline. Get that position in writing before framing.
We build accessory dwelling units across the Merrimack Valley — supervised by Matthew Moisan under Massachusetts Construction Supervisor License CS-119855 — and we carry the permit set, the site plan review and the inspections. Tell us the address and we will tell you what the lot actually allows.