ADU laws in Connecticut

In plain words

Connecticut has had a statewide ADU law since 2022, but it has big gaps. An accessory dwelling unit, or ADU, is a small separate home with its own kitchen on the same lot as a larger main house. It can be inside the house, attached to it, or a separate backyard building. The law says towns must allow at least one ADU "as of right" on every lot with a single-family home. As of right means the town reviews it by checking written rules, with no public hearing and no special permit (an extra approval a board can refuse), and must decide within 65 days. Towns cannot require more than one parking space, cannot demand that the tenant be a relative, and cannot set the maximum size below 30% of the main house or 1,000 square feet, whichever is smaller. They can still ban short-term rentals. The catch: towns were allowed to "opt out" before January 1, 2023, and about two-thirds of them did. In those towns, local rules decide, and some require a special permit or that the owner live on site (an "owner occupancy" rule). Since October 1, 2026, the law also covers cities whose zoning (local rules on what can be built where) comes from their own special laws. A 2026 bill to end all opt-outs died. Check your town's rules first, because you can build only if your local rules and your property allow it.

The rules at a glance

What to do next

1. Ask your town's zoning office whether it opted out of CGS 8-2o before January 1, 2023, and request its current ADU regulations in writing.
2. If your town is covered, ask for the as-of-right ADU application and note the 65-day decision deadline.
3. If your town opted out, find out whether ADUs need a special permit, a public hearing, or owner occupancy there.
4. If your lot uses a well or septic system, talk to your local health district early about capacity.
5. Ask whether your property is inside a transit-oriented district created under PA 25-1, where long-time owners can build an ADU as of right even in opted-out towns.
6. Price utility hookups knowing that most utilities cannot charge an ADU as a new home or force a separate connection.

What your town still decides

The opt-out window closed on January 1, 2023, so no town can opt out now, but towns that opted out before that date are still out. A September 2023 count by the advocacy group Desegregate Connecticut, reported by CT Mirror, found that 115 of the state's 169 towns opted out and 54 did not; 59 of the opted-out towns still allow ADUs under rules that fully or partly match the state standards. The small-towns group COST repeated the 68% opt-out figure in March 2026 testimony and said that, counting all towns, 101 allow ADUs as of right and 55 by special permit. Neither count is an official state list. In covered towns, as of right means the zoning office checks the application against written rules and site plan standards, with no public hearing, variance or special permit, and must decide within 65 days unless the applicant agrees to more time. A covered town that never updated its rules must judge ADUs by the state standards alone and may not add others. Where a well or septic system serves the lot, health-code rules still apply, but approval cannot be unreasonably withheld. In opted-out towns, ADU rules vary widely: some allow ADUs as of right, some need a special permit and hearing, and some require the owner to live on site. The statute does not mention owner-occupancy, and a 2026 bill that would have banned owner-occupancy requirements died. CGS 8-2o does not address homeowners' association rules or private deed restrictions.

What we’re still confirming

• There's no official state list of which towns opted out of the state ADU law; ask your town whether it did.
• Whether towns that wrote their own ADU rules can still require the owner to live on site is legally unsettled.

Laws, bills and citations

This is general information, not legal advice. Your town, village, city or county decides what can be built on your property. If something here looks out of date, email the team.