Southern New Hampshire ADU builder
ADU Builder in Nashua, NH
Short answer: since July 1, 2025, New Hampshire law (HB 577) lets homeowners build one accessory dwelling unit, attached or detached, by right in any zone that allows single-family homes. FJ Global Custom Builds designs and builds ADUs in Nashua, Hudson, Salem, Pelham, Windham, Merrimack and Londonderry.
NH ADU rules in plain English
- One ADU per home, attached or detached, allowed by right (no special exception).
- Towns cannot cap the size below 750 sq ft; the default maximum is 950 sq ft unless your town allows more.
- Towns may require the owner to live in one of the two units, but cannot say which one.
- Towns cannot require a family relationship between occupants or limit the ADU to one bedroom.
- Towns can require no more than one extra parking space.
Types of ADUs we build
- Detached backyard ADU
- Attached ADU / in-law suite addition
- Garage conversion
- Basement ADU
FAQ
Can I build a detached ADU in Nashua?
Yes. Since July 1, 2025, NH towns must allow one attached or detached ADU by right where single-family homes are allowed.
How big can an ADU be in New Hampshire?
Your town cannot limit it below 750 sq ft. Without a local rule allowing more, the maximum is 950 sq ft.
Do I have to live on the property?
Your town may require that the owner lives in either the main house or the ADU.
How much does an ADU cost?
Costs are similar to Massachusetts: roughly $275 to $450 per square foot for new construction. See our ADU cost guide.
This page is general information, not legal advice. Confirm local rules with your town's building or planning department.
Related services and guides
Planning an ADU in southern NH? Free estimate: (781) 527-9445.
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