Durham, New Hampshire
Durham, NH Accessory Dwelling Unit (ADU) Rules
City Acceptance Rating: 8/10
Last Updated: 8.28.2024
Image Source: Derry Community Access Media
What You Need To Know
Attached & detached ADUs are allowed and can not exceed 850 square feet. The homeowner must occupy the primary residence or ADU. Minimum occupancy is 4 weeks.
Type of ADU Permit Required
A conditional Use Permit is required before any building permit will be issued. Applications shall include proof that the following relevant requirements have been met.
ADU Rules
Must be between 500 and 750 square feet, with a total area not exceeding 850 square feet or the size of the primary dwelling.
Limited to a maximum of two bedrooms.
Must not increase any nonconforming aspects of the primary structure or cause a conforming lot to become nonconforming.
No additional driveway is allowed, but at least one off-street parking space per bedroom is required.
The property owner must live in either the primary dwelling or the ADU.
Minimum occupancy for an ADU is four weeks.
Business use of an ADU is limited to a home occupation.
The ADU’s appearance, style, color, and design must match the primary dwelling or structure to which it is attached.
ADUs cannot be used for transient or temporary housing like hotels, motels, or boarding houses.
On conforming lots, ADUs can be attached, detached, or standalone; on nonconforming lots, only attached ADUs are permitted.
ADUs cannot be built with a duplex or multifamily dwelling and cannot attain the status of a duplex or multifamily dwelling.
Attached ADU Standards:
Must be contiguous to the primary dwelling.
Must share a common wall, floor, or ceiling with the primary dwelling.
Must have an interior door connecting the primary dwelling and the ADU.
Detached ADU Standards:
Permitted on conforming lots if they meet building requirements, including setbacks, water supply, septic, and driveway regulations.
Standalone ADU Standards:
Allowed only on lots with an area 50% larger than the required size for a conforming lot.