Accessory Dwelling Unit (ADU) Rules for Plymouth, CT

ADU State Law

What can you build in Connecticut?

• –Connecticut Public Act 21-29 (now CGS § 8-2o) established statewide ADU rules.
• –115 municipalities opted out of the state ADU provisions. In those towns, ADUs may still be allowed, but they are regulated solely under local zoning bylaws.
• –54 municipalities did not opt out and are subject to the state's default ADU standards. Local bylaws in these towns must allow at least the minimums required by state law.
• –At least one accessory apartment must be allowed as of right on any lot with a single-family home.
• –Towns must allow an ADU to be at least the lesser of 1,000 sq ft or 30% of the principal dwelling's Net Floor Area.
• –Setbacks, lot size, building frontage, lot coverage, height, and design requirements cannot be more restrictive than those applied to the principal dwelling.
• –Only one parking space can be required per ADU.
• –A passageway between units
• –A separate exterior entrance (unless required by code)
• –A relationship (e.g. familial or employment) between occupants
• –Age minimums for ADU tenants
• –Separate utility billing
• –Periodic permit renewals
• –Owner-occupancy is not required under state law, but towns may impose it.
• –Towns may regulate short-term rentals.
• –Requirements for wells or private sewerage systems still apply, but approval cannot be unreasonably withheld.
• –Towns may not condition ADU approval on fixing unrelated nonconformities on the lot.
• –No new utility connection fees may be charged unless the ADU is built with a new principal dwelling.