Billerica permits an accessory dwelling unit as of right, but does it in an unusual way: the use table says yes and the bylaw says nothing else. There is no ADU definition and no local standards section, so the state regulation supplies the entire rulebook. The cost to watch is not the permit. It is the sewer charge.
The town fully recodified its zoning, approved at the 2025 Annual Spring Town Meeting. Appendix A, the Table of Use Regulations, lists Accessory Dwelling Unit as permitted as of right in VR, NR, RR, MF, NB and GB, and prohibited in the C and I districts.
What is striking is what is missing. The bylaw contains no ADU standards section and no ADU definition — Section 2 defines only “In-Law Apartment.” The practical effect is clean: an ADU here is a by-right building permit governed by the state regulation for size, parking, separate entrance and the prohibitions, plus your district’s dimensional rules. No local cap. No local deed restriction. No local short-term-rental prohibition.
Your cap is therefore the state figure: 900 square feet or half the principal dwelling’s gross floor area, whichever is smaller.
The legacy In-Law Apartment route survives — ZBA special permit, occupants must be related, maximum two individuals — but there is no reason to use it when the ADU route is by right and less restrictive.
The bylaw is silent on ADUs but not on dimensions, and two footnotes catch people:
One footnote runs the other way and helps: green strip and green space requirements apply to non-residential and non-agricultural uses only, so they do not touch an ADU.
District minimums: VR is 30,000 sq ft with 150 feet of frontage; NR 40,000 and 175; RR 50,000 and 200. All three run 35-foot front, 15-foot side and 20-foot rear setbacks at two and a half stories or 35 feet.
Billerica runs roughly 200 miles of sewer collection main under a long phased program extending service across town. Where sewer reaches your parcel, an ADU is a tie-in rather than a septic redesign, and the risk drops sharply.
The cost is another matter. A new residential sewer permit is $150 plus a DPW fee of $1.97 per square foot, which includes the wastewater and water conservation components. On a 900 square foot ADU that is roughly $1,923 — the largest confirmed per-unit utility charge of any town we have checked, and one that does not appear in any zoning conversation.
All work must be performed by an approved drain layer, and sewer applications have been online-only since 1 January 2024.
Stretch Code, effective 1 July 2018. Specialized Code not adopted. Expect a HERS rater targeting 52–58 with the existing house excluded from the rating, a 50-amp EV-ready circuit per dwelling unit within six feet of a parking space, and a solar-ready zone on a qualifying new detached unit.
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 building permit fee schedule — we could not retrieve it and will not quote a Billerica permit fee we have not read. The sewer figures above are separately confirmed and stand.
Also unconfirmed: the operative text of §9.3 on nonconforming structures, the multi-family dimensional row, the town’s own ADU guide and its administrative checklist, whether building permits file through an online portal, plan review turnaround, what percentage of the town is sewered and which neighbourhoods are not, whether the Board of Health has rules beyond Title 5, and whether a demolition delay bylaw exists in the general by-laws.
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.