ADU rules in Stamford

Stamford wrote its own ADU rules (App. 222-28, effective 10/11/2022) and opted out of the state ADU statute in 2022, and they allow detached ADUs behind 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 state's one-ADU-per-single-family-lot rule, which since 10/1/2026 also reaches special-act cities like Stamford, does not override this gate because Stamford completed its opt-out before the 1/1/2023 deadline (see caveats).

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 CGS 8-2o(a)(3) (the lesser of 30 percent of the principal dwelling's net floor area or 1,000 sq ft), which Stamford's completed 2022 opt-out keeps inapplicable even though P.A. 26-7 extended 8-2o to special-act cities on 10/1/2026. 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. CGS 8-2o(e) bars towns still bound by the statute from imposing standards beyond subsections (a) to (d), but Stamford completed the formal 8-2o(f) opt-out before the 1/1/2023 cutoff (Zoning Board public hearing and 3-0 vote on 10/31/2022; Board of Representatives Resolution No. 4156, 38-0-0, 11/7/2022), so the local requirement stands even now that P.A. 26-7 extends 8-2o to special-act cities. A 2026 bill that would have banned owner-occupancy requirements statewide (HB 5507) died in the House.

Stamford's regulation requires one off-street space for the ADU in addition to the principal dwelling's parking (two to three spaces depending on the Parking Category in Section 12, Map 12.8); the ADU space may not be blocked by the principal dwelling's required spaces, and no additional curb cuts are permitted. State law cuts against this rule: since 7/1/2026 amended CGS 8-2(d)(9) bars minimum off-street parking for residential development except as provided in CGS 8-3n (minimums only for developments of more than sixteen units, or inside an adopted conservation and traffic mitigation district), and CGS 8-3o expressly makes those provisions binding on regulations adopted under a special act, so the bar reaches Stamford whatever the fate of its 8-2o opt-out. The city's pending compliance amendment, Application 226-27 (public hearing opened 9/28/2026, continued to 10/26/2026), would rewrite Section 12 and as noticed lists 'Residential, Single Family, Accessory Dwelling Unit' at 0 spaces in Parking Categories 1 and 3 and 1 per unit in Category 2; on 10/19/2026 the Board asked staff to split out only the state-mandated changes, so the final text may differ. Until it is adopted, the codified one-space rule is what is printed and likely applied at the counter; the value records that local rule with the binding state bar flagged.

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); CGS 8-2o(a)(7)(B) preserves a town's power to ban ADU short-term rentals in any event. The principal dwelling and the ADU 'must remain under common ownership', so the ADU cannot be sold or condo-split separately.