Q: How Do New Hampshire’s ADU Law Changes Affect Property Owners?
A: Recent amendments to New Hampshire’s accessory dwelling unit (“ADU”) statutes have expanded opportunities for property owners across the state to make more flexible use of residential property. The changes took effect on July 1, 2025, and municipalities and property owners alike are continuing to evaluate how the amendments apply in practice.
N.H. RSA § 674:72, I, requires municipalities to allow at least one ADU, by right, on lots within districts where single-family dwellings are permitted. An ADU is defined as a residential living unit located on a lot with a principal single-family dwelling that provides independent living facilities, including facilities for sleeping, cooking, eating, and sanitation. The ADU may be either attached or detached from the principal residence.
The requirement that municipalities permit ADUs “by right” represents a significant shift from prior practice. Previously, municipalities could require a special exception or conditional use permit for ADUs. Under the amended statute, at least one ADU must be permitted without discretionary zoning approval, subject to generally applicable zoning and building requirements. This change reflects a legislative intent to reduce barriers to the development of ADUs and the legislature’s broader efforts to expand housing opportunities throughout the state.
Although state law establishes baseline requirements, municipalities may continue to apply otherwise applicable zoning and development standards, such as setbacks and lot coverage, as long as those requirements are not more restrictive than those applicable to single-family dwellings in the same district. In practice, these dimensional requirements can determine whether an ADU is feasible and may constrain its size or location.
At the same time, the statute limits local discretion. Municipalities may require owner occupancy of one of the dwelling units but may not specify which unit the owner must occupy. Under state law, the total living space of an ADU may not exceed 950 square feet unless otherwise authorized by the municipality; however, a municipality may not restrict the total living space to less than 750 square feet. The statute also limits the extent to which municipalities may impose parking requirements for ADUs, and municipalities may not require that occupants of an ADU be related to the occupants of the principal dwelling.
Because the statutory amendments took effect relatively recently, municipalities may still be evaluating whether local ordinances align with current state law. Property owners considering an ADU should review both state and applicable local laws when evaluating ADU development opportunities. Careful review of applicable requirements can help ensure that an ADU proposal is feasible before investing in design or construction.
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