One Accessory Dwelling Unit is permitted on a lot where there is an existing principal single-family or multi-family dwelling. The information on the application for an Accessory Dwelling Unit should be consistent with information provided when applying for the building permit.
(1) Within an existing principal structure (2) In an accessory structure (3) Within the Building Envelope Dimensions.
City Squared is the City of New Haven’s online Building Permit Application portal. To complete an online Building Permit Application for an accessory dwelling unit, you must create a free City Squared account. When you register for the first time, you will need to access your email account in order to activate your City Squared account. Please reference instructions in How to Use City Squared to avoid delays or issues with your application.
The person completing the online City Squared application should be the primary point of contact for the project and must provide authorization from the property owner. All automatic notifications from City Squared on the application’s status, approvals, and staff comments will be sent to the primary point of contact’s email address. Only the primary point of contact can add additional information to the application once it has been submitted.
Upon review, the City of New Haven Office of Building Inspection and Enforcement may also require additional information and/or exhibits as needed to illustrate the scope of the project. As part of this step in the process, the City Plan Department shall evaluate the proposal’s zoning compliance.
You will be notified through City Squared if your permit application is denied. A reason for denial will typically be provided. If you require additional explanation you may confer with the New Haven City Plan Department staff about possible next steps and whether land use approvals are required before re-submitting your application.
Accessory Dwelling Unit (ADU): A residential living unit that is on the same parcel as a single-family dwelling or a multifamily structure. The ADU provides complete independent living facilities for one or more persons, including space for living, sleeping, cooking, and eating and sanitation.
Interior ADU: A residential living unit that located within the building envelope of an existing primary residential structure and located as a subdivision of existing living space including but not limited to basement and attic spaces.
Attached ADU: A residential living that is located within an addition to an existing primary residential structure with a separate entrance.
Detached ADU: A residential living that is located in an accessory structure that is structurally separate from the primary residential structure.
Affordable housing: The term "affordable housing," "affordable rental housing" or "housing affordable to rental households" is housing that costs no more than 30% of household income for rent and utilities, for households earning 60% or less of area median income. Unless otherwise specified by funding sources, or other agreement made with the City of New Haven, deed restricted units shall remain affordable for a period of 40 years after following issuance of the last certificate of occupancy for the qualifying development. In multi-phased qualifying developments, the period of affordability may begin upon issuance of the last certificate of occupancy for each phase, at the discretion of the Affordable Housing Commission.
Principal structure: A building in which is conducted, or is intended to be conducted, the principal use of the lot on which it is located.
Gross floor area: The sum of the gross horizontal areas of the several floors of a building, measured from the exterior faces of exterior walls (and from the center lines of party walls if the portions of the building separated by such party walls are to be treated separately), including:
(1) Basement space where more than one-half the basement height is above the finished lot grade average along the exterior walls of the building;
(2) Elevators and stairwells at each floor;
(3) Attic space, whether or not a floor has been laid, over which there is structural headroom of seven foot or more; and
(4) Enclosed porches, interior balconies and mezzanines, and penthouses; and excluding floor space permanently devoted to mechanical equipment used in the operation and maintenance of the building, and floor space permanently devoted to a parking space or parking spaces.
Coverage: The proportion of the lot area, expressed as a percent, that is covered by the maximum horizontal cross section of a building or buildings. Structures which are below the finished lot grade, including shelters for nuclear fall-out, shall not be included in building coverage.
Building Envelope Dimensions: The complete three-dimensional form of a structure including the structure’s area, footprint, bulk, height, and mean roofline.
Height: The vertical distance from the average elevation of the finished lot grade to the highest point of the ceiling of the top story of a building or structure in the case of a flat roof, to the deck line of a mansard roof, and the average height between the eaves and ridge of a gable, hip or gambrel roof.
Dwelling: A building containing one or more dwelling units; but in the case of a building having two or more portions divided by one or more party walls forming a complete separation, each such portion shall be considered to be a separate building.
