ADU rules in Stamford

Stamford wrote its own ADU rules (App. 222-28, effective 10/11/2022) after opting out of the state ADU statute, and they allow detached ADUs but with a gate that commonly bites: an ADU (attached or detached) is allowed only on a lot that contains no more than one single-family dwelling AND has a lot area of at least 10,000 sq ft. That excludes conforming lots in the R-7 1/2 district (7,500 sf minimum) and most R-6 single-family lots (5,000 sf minimum), even though single-family homes are permitted there. A detached ADU must meet either the accessory-building standards or the district's single-family dwelling standards, and only one ADU is allowed per single-family dwelling. Two-family and multi-family properties, including legally nonconforming two- and three-family dwellings, are ineligible, and on septic lots the Health Department and EPB must first find the system sufficient for both units.

The same regulation allows the ADU to be 'attached to or within the Principal Dwelling Unit' (basement, addition, or internal conversion), subject to the identical gates: a lot with no more than one single-family dwelling, at least 10,000 sq ft of lot area, one ADU maximum, and owner occupancy. Attached ADUs and ADUs within the principal dwelling must meet all requirements of the underlying zoning district. In single-family districts the ADU is excluded from the one-dwelling-per-lot density cap (Section 5.X.4.d note 1), so adding one does not make the lot nonconforming as to density.

The ADU may not exceed 800 sq ft of gross floor area, and by definition the principal dwelling must keep the larger gross floor area of the two units. Occupancy of the ADU is capped at three persons. There is no percent-of-primary alternative: the 800 sf figure is a flat cap, stricter for larger homes than the floor in the state statute Stamford opted out of (CGS 8-2o would have required the lesser of 30 percent of the principal dwelling's net floor area or 1,000 sq ft). Detached ADUs take their height and setback limits from either the accessory-building standards or the district's single-family standards.

Condition 1 of the ADU regulation: 'The property owner must reside on the premises.' The owner files an affidavit of residence when applying for the ADU building permit, and the residence requirement is written as a standing condition of the use, not a one-time test at application. Connecticut's ADU statute never prohibited owner-occupancy mandates, and Stamford in any event completed the formal CGS 8-2o(f) opt-out (Zoning Board unanimous 10/31/2022; Board of Representatives Resolution No. 4156, 38-0-0, 11/7/2022), so the local requirement stands on its own.

One off-street parking space is required for the ADU in addition to the parking required for the principal dwelling, whose base requirement is two to three spaces depending on the property's Parking Category under Section 12 (Map 12.8); the ADU space may not have its access blocked by the principal dwelling's required spaces, and no additional curb cuts are permitted. State law has moved under this rule: the former CGS 8-2p parking caps Stamford opted out of in 2022 (Res. No. 4157, 11/7/2022) were repealed effective 1/1/2026 (Nov. Sp. Sess. P.A. 25-1, S. 53), and since 7/1/2026 amended CGS 8-2(d)(9) bars requiring any minimum off-street parking for residential development except as provided in new CGS 8-3n, which allows minimums only for developments of more than sixteen dwelling units and bars parking-based rejections absent a specific adverse public-health-and-safety finding. For parking, unlike 8-2o, the special-act question is resolved by statute: CGS 8-3o (P.A. 25-1, S. 20, eff. 7/1/2026) expressly requires regulations adopted under special-act zoning authority to comply with 8-2(d)(9) and 8-3n, so the state bar binds Stamford despite its special-act charter. Stamford's codified rule still prints the one-space requirement and the city had not amended it or published guidance as of 08/2026, so expect it to be applied at the counter; the value records the codified local rule with the binding state preemption flagged per the both-texts convention.

ADUs are approved by Zoning Permit, an administrative permit issued by the Zoning Enforcement Officer or their designee with no public hearing. Under Section 2.G.3 the ZEO must grant or deny within 30 days of a complete application and may deny only for non-compliance with the Regulations, incompleteness, or false statements. A building permit (with the owner-residence affidavit) follows; a Certificate of Zoning Compliance is required before occupancy. On unsewered lots the Zoning Permit cannot issue until the Health Department and EPB find the septic system sufficient for both units.

Nothing in the ADU regulation restricts renting the unit on ordinary leases, but occupancy of the ADU is capped at three persons and the owner must reside on the premises, so a fully absentee rental configuration is not possible. Short-term rental of an ADU is flatly prohibited: condition 10 of the ADU regulation and the separate Short-Term Rental standards (App. 223-10, eff. 6/7/2023) both state that ADUs shall not be used as short-term rentals, defined as stays of 1 to 27 consecutive days (and capped at 90 rental days per year where STRs are allowed at all). The principal dwelling and the ADU 'must remain under common ownership', so the ADU cannot be sold or condo-split separately.