Darien ADU Zoning Guide

Last reviewed 2026-04-28

Max size700 sq ft
Owner occupancyRequired

Darien, CT permits accessory dwelling units under Amendment 94 (COZR #1-2024), adopted by the Planning and Zoning Commission on May 7, 2024 and effective June 30, 2024. ADUs are allowed on single family lots in the R-2, R-1, R-1/2, R-1/3, and R-1/5 zones. Lots of 1 acre or more take a by-right administrative path; lots under 1 acre go through Site Plan approval by the Planning and Zoning Commission. The amendment carries a five year sunset clause and expires June 30, 2029 unless extended. Darien opted out of Connecticut's Public Act 21-29 and Amendment 94 is the local replacement.

Status

Adoption status: Active. Amendment 94 (COZR #1-2024) adopted May 7, 2024 by the Darien Planning and Zoning Commission, effective June 30, 2024 at 12:01 p.m.
Governing ordinance: Darien Zoning Regulations Sections 210 (definitions), 403.o, and 407.c, as amended by Amendment 94 / COZR #1-2024
Key differentiator: Tiered permit pathway by lot size (1 acre threshold), 5 year sunset clause to June 30, 2029, and explicit prohibition on stays under 90 days as the short term rental ban.

Eligibility

Where ADUs are allowed

Zoning districts permitted: R-2, R-1, R-1/2, R-1/3, R-1/5
Excluded districts: Noroton Bay District (R-NBD) and Darien commercial zones
Lot type: Single family lots
Limit per property: One ADU per lot. Common ownership required; parcel may not be subdivided.

Types allowed

Attached ADU (within or adjoining principal): Yes (700 sq ft cap)
Detached ADU (separate accessory building): Yes (1,000 sq ft cap)
Garage conversion: Yes
Sheds / cargo containers / RVs: Prohibited
Substandard accessory structure conversion: Prohibited

Size and placement

Size limits

Maximum sq ft (attached): 700 sq ft
Maximum sq ft (detached): 1,000 sq ft
Maximum percentage: 30 percent of combined principal plus ADU floor area

Setbacks

Setback requirements: Same as for a principal structure in the underlying zoning district. Standard building height and building coverage rules apply.

Rules for use

Parking

Principal dwelling: 2 spaces required (existing rule)
Studio or 1 bedroom ADU: +1 additional on site space
Multi-bedroom ADU: +1 space per additional bedroom

Owner occupancy

Required: Yes. The record owner must reside in either the principal dwelling or the ADU.
Annual affidavit: Initial plus annual affidavit required
Separate sale permitted: No. ADU cannot be sold separately or condominiumized.
Deed restriction: Recorded on the Darien Land Records
Hardship exception: Up to 3 years of non-occupancy possible by Special Permit due to unusual or unforeseen circumstances

Rental use

Short-term rental: Prohibited. Neither the ADU nor the principal dwelling may be used for stays under 90 consecutive days (transient stays as defined in Section 210).
Long-term rental: Permitted, subject to owner occupancy of either unit

How to apply in Darien

Lots of 1 acre or more: Administrative. Staff review with Zoning Permit and Building Permit.
Lots under 1 acre: Site Plan approval required from the Planning and Zoning Commission, plus Zoning Permit and Building Permit
Contact: Darien Planning and Zoning Commission

Recent and pending changes

2024-05-07
Amendment 94 (COZR #1-2024) adopted by P&Z, permitting ADUs in R-2, R-1, R-1/2, R-1/3, R-1/5 with size caps, owner occupancy requirement, no short term rental, and a 5 year sunset.

Important details

Sunset clause: Amendment 94 expires June 30, 2029. Applications received and built (Certificate of Zoning Compliance plus Certificate of Occupancy) by June 30, 2030 remain legally conforming.
Tiered permit pathway: lots of 1 acre or larger qualify for staff review and a Zoning Permit. Lots under 1 acre go to Site Plan review with the Planning and Zoning Commission.
Transient definition: stays of less than 90 consecutive days are prohibited for both the ADU and the principal dwelling. This functions as the short term rental ban.
Deed restriction: Amendment 94 requires a deed restriction recorded on the Land Records preventing separate sale of the ADU.

Frequently asked questions

Where in Darien are ADUs allowed?

Single family lots in the R-2, R-1, R-1/2, R-1/3, and R-1/5 residential zones. Together these cover roughly 90 percent of Darien. The Noroton Bay District (R-NBD) and commercial zones are excluded.

How big can my Darien ADU be?

An attached ADU is capped at 700 square feet. A detached ADU is capped at 1,000 square feet. In both cases, the ADU also cannot exceed 30 percent of the combined floor area of the principal dwelling plus the ADU. All caps apply together.

Will the rules expire?

Yes. Amendment 94 carries a five year sunset and expires June 30, 2029 unless the Planning and Zoning Commission extends it. ADUs applied for by June 30, 2029 and that obtain a Certificate of Zoning Compliance and Certificate of Occupancy by June 30, 2030 remain legally conforming.

Sources (3)

Last reviewed 2026-04-28. Local rules can change — verify the latest details with the Darien planning department, or book a free consultation with our team before starting your project. This page is informational and is not legal advice.