ADU Guide · Verified 2026
Building an ADU in Connecticut
Connecticut required ADUs as of right in every municipality zoning under CGS 8-2, but gave towns a real opt-out window: any town could vote itself out of the mandate before January 1, 2023, if both its Planning and Zoning Commission and its Board of Selectmen agreed. Dozens of towns took that option, so the real question in Connecticut is always whether the specific town opted out.
Quick Facts
Statewide floors set by HB 6107 / Public Act 21-29 (2021). Your city may be more generous but cannot go below them.
The Three Types of ADU
A real, formal opt-out mechanism, unique in this research
Connecticut is the only state covered here where a town could vote itself entirely out of the statewide ADU mandate through a genuine, documented process: both the Planning and Zoning Commission and the Board of Selectmen had to agree, before a hard January 1, 2023 deadline. Dozens of towns did.
A real example of what opting out looks like
West Haven formally opted out of PA 21-29 and enforces its own local ADU rule instead, capping units at 550 square feet, a real, documented case of a town choosing its own standard over the state default.
Parking shows how much local variation survives
PA 21-29 bars additional parking requirements by default, but Branford requires parking unless the ADU is built into the existing structure, while Milford explicitly removed its own parking requirement, two real, opposite local choices under the same nominal state law.
What people get wrong
The most common mistake is assuming PA 21-29 applies uniformly across Connecticut. The real first question in any Connecticut ADU project is whether the specific town opted out before the January 1, 2023 deadline, since a town that did runs entirely on its own rules.
From Idea to Move-In: The Timeline
Who Administers It
Building It Yourself? Here's What You'll Need
Planning an ADU? Tools homeowners use in the design and layout phase:
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Check Your Local Rules
Your city may allow more than the state floor
State law sets the minimum; many Connecticut cities and counties are more generous. Browse the full directory of 8 counties and every city in Connecticut for local rules, fees, and building department contact details.
Browse the full Connecticut directory →Not sure if your project needs a building permit, a zoning approval, or both? See our guide to building permits vs. zoning approval.
Official Sources
ADU law changes frequently and local ordinances add detail. This guide is general information, not legal advice, always confirm with your local building department. Reviewed by the StateDataIndex Editorial Team · Updated September 2026.