Manchester, NH Accessory Structures: ADU Rules (2026)

Manchester's Building Sewers chapter singles out detached accessory dwelling units for a specific hookup rule, added by amendment on January 7, 2025. 122, the general rule is that every building gets its own independent building connection to the public sewer, though the Public Works Director can allow two or more buildings to share one connection when separate lines would cause practical difficulties. Detached ADUs get a distinct third path: rather than sharing the general shared-connection option available to multi-family, condominium, or town house units, an ADU must connect to the sewer service already serving the main dwelling on the same parcel, with the tie-in point located downstream from where that service exits the main house.

Because this is treated as a new hookup, the owner must file a separate application for a new sewer connection permit before the work is done, even though the lot already has active sewer service. 121: the owner bears every cost of installation and connection, and permit issuance is conditioned on the owner indemnifying the city against loss or damage the work causes. 118, and may install connections only during normal city working hours unless the Department approves emergency hours in writing. This sewer hookup duty is separate from where an ADU can physically sit on a lot: setbacks, size caps, and other dimensional standards for accessory dwelling units come from Manchester's Zoning Ordinance, which is published apart from the general Code of Ordinances and is not covered by Chapter 52.