ADU rules in New Britain

A freestanding backyard cottage is not allowed. Zoning Ordinances Section 270-40-40.290.10.80 requires that an accessory dwelling unit 'be constructed within the building envelope or attached to the existing principal structure with a common wall of at least eight (8) feet in width', so an ADU must be carved out of the house or built as an addition sharing at least 8 feet of wall. New Britain reached this result by opting out of CGS 8-2o on 12-14-2022 (Common Council Item 35947), and the opt-out resolution named the statute's detached allowance as one of its reasons, so the statewide rule that detached accessory apartments be permitted as of right does not reach the city. The City Plan Commission's report on the 2022 ordinance said the intent was to allow ADUs 'as more of a traditional in-law suite that is within or attached to the principal residence'. Reinforcing rules require the unit to share the principal structure's utilities and meters and to carry the same street number.

Attached and interior ADUs are allowed, but only as a special exception use in four residential districts and only on larger lots. Sections 60-20-140 (S-1), 70-20-150 (S-2), 80-20-150 (S-3) and 90-20-10.10 (T) list 'Accessory dwelling unit' among the special exception uses 'permitted, subject to approval by the Zoning Board of Appeals pursuant to Section 270-40', with site plan review under Section 280-60. Section 270-40-40.290.10.10 adds that ADUs 'shall be constructed only on lots totaling more than eight thousand (8,000) square feet', which is a real gate: the minimum lot area is 8,000 sq ft in S-2 and 6,000 sq ft in both S-3 and T, so a conforming lot in those three districts does not qualify and only S-1 (13,500 sq ft minimum) clears the threshold automatically. No ADU listing appears in the T-6, A-1, A-2, A-3 or any nonresidential district, and Section 30-20-10.10 defines the use as a unit 'subordinate to the primary residence on a single-family home parcel'.

Section 270-40-40.290.10.40 caps the unit at 'forty (40) percent of square footage of the existing principal structure on parcel or eight hundred (800) square feet; deferring to the lower value', so 800 sq ft is the ceiling and any house under 2,000 sq ft is held below it. Two further caps compound the size limit: Section 270-40-40.290.10.60 allows 'no more than one (1) bedroom', and Code of Ordinances Sec. 25-1 provides that 'At any given time, no more than two (2) persons shall occupy an accessory dwelling unit.' Section 270-40-40.290.10.20 otherwise makes the ADU meet the ordinary dimensional requirements of its district (setbacks, coverage, height). Because New Britain opted out of CGS 8-2o, the statutory floor of the lesser of 30% of net floor area or 1,000 sq ft does not bind it; the local formula is more generous than the state floor for small houses and less generous for large ones.

Owner occupancy is mandatory and continuing, and it lives in the Code of Ordinances rather than the zoning book. Sec. 25-1 provides that 'No owner of a property may construct and maintain an accessory dwelling unit without claiming one (1) unit on said property as permanent residence', limits the property to one ADU, and requires a signed and notarized affidavit before the certificate of occupancy issues. Compliance is policed annually: the owner 'must submit annually to the zoning department via online permitting system or hand delivery to office a copy of owner's homeowner insurance policy to serve as proof of continued occupancy', and failure exposes the owner to 'enforcement action including, but not limited to, fines and/or demolition order of the subordinate structure/accessory dwelling unit'. CGS 8-2o never prohibited owner-occupancy conditions (they are absent from its subsection (a)(6) list), so this requirement would have survived even without New Britain's opt-out.

Section 270-40-40.290.10.30.10 requires that 'Three (3) off-street parking spaces shall be provided: two (2) spaces per existing principal structure and one (1) space per accessory dwelling unit', so on the books the ADU adds one space to the two the house already owes under the Section 240-20 residential schedule. Section 270-40-40.290.10.30 also bars new access: 'No accessory dwelling unit shall be served by additional curb cuts beyond the existing curb cut in place for the existing principal structure', which on a narrow lot is often the harder constraint. State law has since overtaken the number. Since 07-01-2026 CGS 8-2(d)(9) has provided that zoning regulations shall not 'Require a minimum number of off-street motor vehicle parking spaces for any residential development except as provided in section 8-3n', and new CGS 8-3n permits minimums only for a residential development of more than sixteen dwelling units. A house plus one ADU is nowhere near that threshold, so the three-space requirement is no longer something the city may impose, and CGS 8-3n(a) separately bars rejecting a residential application solely for failure to meet a parking requirement unless the officer or commission finds a specific adverse impact on public health and safety that approval conditions cannot mitigate. The ordinance text still reads three spaces, so ask the Zoning Enforcement Officer how New Britain is applying it.

An ADU needs a discretionary special exception from the Zoning Board of Appeals, not staff sign-off. Each district section provides that special exception uses are 'permitted, subject to approval by the Zoning Board of Appeals pursuant to Section 270-40', and Section 270-40-20.20 requires the Board to 'make a specific finding, after a public hearing in the manner provided by law, that such use will not be prejudicial to the character of its neighborhood'. Section 270-40-20.30 further bars any grant 'until the said Board shall have first received and considered an advisory report thereon from the City Plan Commission', which has 30 days to report. Section 270-40-30 layers on eleven general standards, and the site plan goes to review under Section 280-60. This is exactly the discretionary review CGS 8-2o would forbid for as-of-right accessory apartments; New Britain can require it because it opted out on 12-14-2022.

Renting the ADU on a normal lease is permitted, subject to Code of Ordinances Sec. 25-1: the owner must keep one of the two units on the parcel as a permanent residence, file annual proof of that occupancy, and no more than two people may occupy the ADU. Short-term rental is flatly barred: Zoning Ordinances Section 270-40-40.300.60 provides that 'Accessory dwelling units shall not be used for short-term rentals', where Section 30-20-645 defines a short-term rental as a stay of 'twenty-seven (27) consecutive calendar days or less'. Short-term rentals elsewhere in the city need their own ZBA special exception plus an annually renewed zoning permit under Section 270-40-40.300.10. Nothing in the ordinances allows the ADU to be sold separately from the principal dwelling; it must share the principal structure's utilities, meters and street number.