ADU rules in Danbury

Danbury allows no free-standing backyard cottage anywhere in the city, and that did not change when the city legalized accessory apartments on 7-1-2026. The new use is interior or attached only: Section 3.G.15.b provides that 'The accessory apartment shall be located within, or attached to, the principal one family dwelling unit,' and the blanket rule at Section 3.G.2 that 'No accessory building shall be used as a residence' is unchanged. Section 3.C.1 still closes every district's use list, so a detached second dwelling is prohibited citywide, including inside the Downtown Transit Oriented Development District where the new accessory apartment use lives. The variance door is shut by name: Section 3.G.15.k states that 'Variances to any of the provisions of this section are prohibited,' and Section 11.B.2.g adds that 'No variance shall be granted to allow an accessory apartment in any zone other than is noted in Section 3.G.15.'

Danbury reversed a decade of prohibition on 7-1-2026 and now permits one attached or interior accessory apartment, but only inside the Downtown Transit Oriented Development District (D-TOD), the downtown district drawn around the rail station and Pulse Point. Section 3.G.15 opens: 'An accessory apartment is allowed as an accessory use to a one family detached dwelling in the D-TOD district,' and the D-TOD use table now lists 'Accessory apartment (accessory to one family dwelling)' as a permitted use keyed to Section 3.G, alongside a newly added 'One family dwelling' permitted use. Only one apartment is allowed per lot; it must have its own kitchen and complete bathroom separate from the main house and one on-grade exterior door of its own, and a basement unit is allowed only where the basement is a walk-out approved by the Building Official and Fire Marshal. Everywhere else in Danbury the 2022 opt-out at Section 3.C.7 still stands and no accessory apartment is permitted: Section 4 was not amended, so the four RA single-family districts still list a one family dwelling as their only residential use and still allow 'Only one principal dwelling per lot.'

Section 3.G.15.f sets the cap: 'The maximum floor area of an accessory apartment shall be 30 percent or less of the area of the principal building and not more than 1,000 square feet.' Both limits apply, so on a 2,000 square foot house the binding number is 600 square feet, while 1,000 square feet is the ceiling no matter how large the house. The definition of accessory use in Section 2.B was revised in the same package to make room for this, capping accessory uses at twenty-five percent of the principal use's usable gross floor area 'except for the accessory apartments which may be thirty percent (30%).' If the apartment needs a building addition, Section 3.G.15.g(1) allows it to extend only into the side or rear yard and requires the district's ordinary setbacks to be maintained, which in the D-TOD are zero feet except for a ten-foot buffer where a lot directly abuts an existing residential district. These numbers track the state floor in CGS 8-2o(a)(3), which would have required at least the lesser of thirty percent of net floor area or 1,000 square feet.

Section 3.G.15.e requires that 'Either the principal one family dwelling or the accessory apartment shall be occupied by the owner of the premises,' so an investor cannot rent out both units. The rule has teeth at the occupancy stage: Section 3.G.15.j withholds the Certificate of Zoning Compliance until the owner submits 'A notarized letter ... stating that they will occupy one of the dwelling units on the premises as his/her primary residence,' and Section 3.G.15.l makes violations 'subject to permit revocation and all such fines available pursuant to the Connecticut General Statutes Section 8-12.' A separate gate in the same subsection requires 'Proof ... that the owner has owned the subject property for at least three years,' so a buyer cannot add an accessory apartment immediately after closing. That three-year test is lifted from CGS 8-2o(g), the state provision that lets owners inside a transit-oriented district build an accessory apartment despite a town's opt-out, which is a strong signal Danbury drafted Section 3.G.15 as its implementation of that subsection.

The 7-1-2026 amendment added a dedicated row to the off-street parking table at Section 8.C.4.f, '(14) Accessory Apartment', requiring '0' spaces, so an accessory apartment triggers no additional parking at all. The house itself keeps the ordinary residential standard in Section 8.C.4.f(1) of 2 spaces per dwelling unit plus 1 per 2 resident employees. Danbury's 2022 opt-out from the state parking caps still appears at Section 3.C.6 but is dead letter: Nov. Sp. Sess. P.A. 25-1, S. 53 repealed CGS 8-2p effective 1-1-2026, and S. 18 rewrote CGS 8-2(d)(9) effective 7-1-2026 to forbid minimum residential parking requirements 'except as provided in section 8-3n,' deleting the opt-out clause. In the same 7-1-2026 package Danbury adopted the two Conservation and Traffic Mitigation District overlays that CGS 8-3n(d) allows, which are now the only parts of the city where it may still impose residential parking minimums below seventeen units, and added a fee in lieu of parking of $15,000 per space for developments of sixteen or more units.

An accessory apartment in the D-TOD is an over-the-counter approval, not a hearing. Section 3.G.15.h requires 'A Zoning Permit in accordance with Section 10.B.,' and Section 10.B.1.d provides that 'The zoning permit shall be issued upon a finding by the Zoning Enforcement Officer that the proposed activity is in compliance with the Zoning Regulations,' with no Zoning Commission review, no special exception and no public notice. The fee schedule adds a line for it: 'The permit fee for an accessory apartment zoning permit shall be $300.00,' nonrefundable. Two extra steps apply before occupancy: a lot served by a private well or septic system needs approval from the Department of Health and Human Services before the zoning permit issues, and the Zoning Enforcement Officer issues a Certificate of Zoning Compliance only once the three-year ownership proof, the completed improvements and the notarized owner-occupancy letter are in hand. Outside the D-TOD there is no pathway at all, and Section 11.B.2.g forecloses using a variance to create one.

Section 3.G.15.c provides that 'An accessory apartment shall not be leased for less than thirty (30) days,' which rules out Airbnb-style short stays while leaving ordinary month-to-month and annual tenancies open. Section 3.G.15.d bars selling the apartment separately from the one family dwelling, so it cannot be split off as a condominium, and Section 3.G.15.e keeps one of the two units owner-occupied as a primary residence. Danbury's Code of Ordinances still contains no short-term-rental licensing or rental-registration chapter: chapter 20 (Housing) holds only a Fair Rent Commission under CGS 7-148b and a Maintenance and Occupancy Code, and chapter 26 covers closing-out sales and entertainment licenses. Renting out an ordinary whole house remains unrestricted by zoning, and CGS 8-2o(a)(7)(B) expressly preserves a municipality's power 'to prohibit or limit the use of accessory apartments for short-term rentals or vacation stays.'