Alton, NH Accessory Dwelling Unit (ADU) Rules

City Acceptance Rating: 10/10

Last Updated: 8.28.2024

What You Need To Know

The purpose of allowing accessory dwelling units is to enhance Alton’s affordable housing options and make better use of existing homes, while preserving the town's rural, one-family residential character. This initiative aims to provide small rental units that support low-income families and improve the overall housing inventory.

Type of ADU Permit Required

By-right if the following requirements are met.

ADU Rules

Subordination and Aesthetics: The ADU must be clearly subordinate to the main residence and maintain the aesthetic continuity of a single-family home.
One Per Lot: Only one ADU is allowed per lot.
Not Considered Additional Unit: The ADU does not count as an additional dwelling unit for lot size or density calculations.
Location: The ADU must be within or attached to a single-family home or within an accessory structure on the same property. No ADU is allowed on lots with more than one dwelling unit.
Lakeshore Residential District: ADUs in this district are only allowed within or attached to a single-family home and require a Special Exception from the Zoning Board of Adjustment. Specific criteria in SECTION 413 do not apply to ADUs in this district.
Bedroom Limit: The ADU can have no more than two bedrooms.
Size Limits:

Maximum of 1,500 sq. ft. of total floor area.
Must not exceed 35% of the total finished floor space of the main dwelling.
If in an accessory structure, it must not exceed 50% of the structure's floor space or 35% of the main dwelling's finished floor space, whichever is less.
Minimum size of 750 sq. ft. is required.

Entrances and Exits: Any new entrances or exits for the ADU must be located on the side or rear of the main dwelling.
Parking: A minimum of four off-street parking spaces must be provided for the main residence and the ADU.
Sewage Disposal: Prior to constructing an ADU, the sewage disposal system must be approved and meet NH RSA 485-A standards. An approved system must be installed if the existing one is not compliant or needs replacement.
Owner Occupancy: Either the main residence or the ADU must be occupied by the property owner.
Interior Door: An interior door must connect the main residence and the ADU if the ADU is within or attached to the main dwelling.
Ownership: The single-family home, ADU, and lot cannot be converted into separate legal ownerships, such as condominiums.
Prohibited with Certain Dwellings: ADUs are not allowed with multiple single-family dwellings, such as townhouses, or with manufactured housing as defined by NH RSA 674:31.

Resources:

https://www.alton.nh.gov/forms/planning/ZoningOrdinance.pdf - page 23

Alton, New Hampshire