Connecticut residential & ADU permit data

Connecticut's Public Act 21-29 (2021), originally House Bill 6107, made accessory dwelling units permitted 'as of right' in single-family zones statewide — but with an unusual local escape hatch that shapes the entire market. By default the law bars a separate special permit or public hearing for a conforming ADU, caps the unit at 1,000 square feet or 30% of the main dwelling (whichever is less), limits required parking to one space, and prohibits towns from restricting the unit's occupancy to family members or imposing an owner-occupancy condition under the state standard.

The catch is the opt-out. The legislature let any municipality opt out of these default ADU standards if both its zoning commission and its legislative body (or town meeting) voted to do so by January 1, 2023. A large share of Connecticut towns took that option — well over a hundred opted out of the as-of-right default, more than the number that fully adopted it — so whether an ADU is truly by-right depends heavily on the specific town. Opting out does not necessarily ban ADUs; it simply lets a town write its own rules, which may be more or less permissive than the state baseline.

That makes Connecticut a patchwork compared with the firmer statewide guarantees in Massachusetts, California, Washington and Oregon, none of which handed towns a blanket opt-out from the ADU mandate. The practical task for builders and homeowners is mapping which municipalities kept the as-of-right standard and which replaced it with local regulation before assuming a backyard unit is permitted. Even in an opt-out town an ADU is often still allowed under a local special-permit or zoning process; it simply is not guaranteed by right, which changes both the timeline and the certainty of approval.

Connecticut also lacks a statewide 'missing middle' upzoning law. A 2025 omnibus housing bill, HB 5002, that would have added transit-oriented and middle-housing provisions was vetoed, leaving residential density to local zoning. Igni sources live Hartford permit data from the city's open data, so ADU and residential permit activity surfaces across the as-of-right municipalities as the market matures.

This is an informational summary, not legal advice; whether an ADU is as-of-right turns on your specific town's opt-out decision, so verify the local ordinance and current statute before relying on it.