ADU rules in Norwalk

Detached backyard ADUs are allowed citywide in residential areas. Table 4.3.9.D (Building, Lot & Building Site Accessory Uses) lists 'Accessory Dwelling Unit' as PL (Permitted by Right with Limitations) in all nine Community Districts, CD-1L, CD-1M, CD-1S, CD-2, CD-3, CD-3W, CD-3C, CD-4 and CD-4W, and NP (Not Permitted) in the five Special Districts (SD-H Hospital, SD-IC Island Conservation, SD-LI Light Industrial, SD-HI Heavy Industrial, SD-MC Marine Commercial) and the Civic District. The ADU must sit on the same lot as a single-family detached dwelling and only one ADU is allowed per lot. A detached ADU that meets the district's principal-building setbacks is an over-the-counter Zoning Permit; one that relies on the looser accessory-building setbacks goes to the Commission for Site Plan Review.

Attached, internal and above-garage ADUs are allowed on the same footing: 'The ADU may be within and/or attached to a Principal Building or Accessory Building' (section 4.3.9.G.4.a(1)(c)). An attached ADU must meet principal-building setbacks and the district's principal-building height, capped at 2 1/2 stories, and 1,000 sq ft of floor area. A principal building that is already nonconforming as to setback or height may convert the nonconforming portion into an ADU so long as every other ADU requirement is met. Attached ADUs are approved by Zoning Permit issued administratively by the Planning and Zoning Director.

Both attached and detached ADUs are capped at 1,000 square feet of Floor Area. Amendment #2026-02 R (effective 4-24-2026) raised the detached cap from 700 sq ft to match the attached cap, so the two are now identical. Article 9 defines an Accessory Dwelling Unit as 'a Dwelling Unit having habitable space not greater than 1,000 square feet which shares ownership and utility connections with the Principal Building.' Height follows the district's principal-building limits for attached ADUs (not to exceed 2 1/2 stories) and the district's accessory-building limits for detached ADUs (not to exceed 1 1/2 stories). A detached ADU is also bound by section 4.3.4.C.3.a, which caps a detached accessory building's footprint at 60 percent of the principal building. An existing legally conforming or legally nonconforming accessory building may be converted to an ADU without meeting the detached setback, height or 1,000 sq ft limits, provided it is not made any more nonconforming.

'The owner of the Lot must reside on the Lot' (section 4.3.9.G.4.a(1)(d)), and the obligation is ongoing rather than only at application: an affidavit verifying that the owner still resides on the lot, that the minimum rental duration is being observed, and that all other conditions met at the time of the original application remain unchanged must be filed with the Planning and Zoning Director by January 31 of each year. This is one of the requirements Norwalk deliberately preserved by opting out; CGS 8-2o would not have barred it either, since owner-occupancy is absent from the 8-2o(a)(6) list of prohibited conditions, but the annual recertification would have run against 8-2o(a)(6)(H)'s ban on periodic permit renewals.

Amendment #2026-02 R deleted the ADU parking requirement outright: section 4.3.9.G.4.a no longer contains a parking clause, where the prior version required one additional off-street space for the ADU (and the pre-2024 code required three spaces total). Parking now comes only from Table 4.3.12.B-1, which expressly counts ADUs as 'Dwelling(s)' and sets dwellings of 16 or fewer units at 'Not Regulated except for within the Traffic Mitigation Districts,' where the requirement is the lesser of one space per studio or one-bedroom unit and two per larger unit, 1.3 spaces per dwelling unit, or the number in an applicant-submitted Parking Needs Assessment. The Traffic Mitigation Districts are drawn on Illustration 4.3.12.B-1 and cover the denser corridor and center areas, not most single-family neighborhoods. Amendment #2026-38 R (adopted 6-17-2026, effective 6-30-2026) restated this table expressly 'to comply with Public Act 25-1.'

Two routes, both without a public hearing. Most ADUs are 'Permitted by Zoning Permit in accordance with Section 8.4.10': every ADU that complies with principal-building setbacks, plus attached ADUs converting a nonconforming portion of the principal building. Table 8.4.3 (Review Authority) makes the Zoning Permit a Planning and Zoning Director decision, appealable to the Zoning Board of Appeals. Detached ADUs that comply only with accessory-building setbacks, and conversions of existing accessory buildings, are 'Permitted by Site Plan Review in accordance with Section 8.4.5,' a Planning and Zoning Commission decision (no hearing required; CGS 8-3(g) site plan certification). For every ADU application, whichever route, the applicant must mail notice by U.S.P.S. with a Certificate of Mailing-Firm to all owners within 100 feet of the lot, and Zoning Permit decisions must be published in a newspaper at the applicant's expense.

'The minimum rental duration of the ADU shall be no less than six (6) months' (section 4.3.9.G.4.a(1)(e)). Combined with the owner-occupancy rule and the January 31 affidavit that recertifies the minimum rental duration each year, that forecloses Airbnb-style short stays in a Norwalk ADU. Norwalk has no separate short-term rental licensing ordinance; the Code of Ordinances chapter list on eCode360 (NO0086, legislation through 5-26-2026) contains no short-term rental chapter, and the zoning regulations define no short-term rental use. An ADU by definition 'shares ownership and utility connections with the Principal Building' (Article 9), so it cannot be sold or conveyed separately from the principal dwelling. CGS 8-2o(a)(7)(B) expressly preserves municipal power to limit ADU short-term rental use, and Norwalk opted out of 8-2o entirely in 2022.