ADU Regulations in New Hampshire (NH)
New Hampshire is rated Moderate for ADU construction with an ADU-friendliness score of 55/100 (ADU-Friendly). New Hampshire has a statewide ADU law that sets baseline rules across all municipalities. Owner must reside on the property. Additional parking may be required. New Hampshire has required all municipalities to allow ADUs since 2017 (RSA 674:71-73). However, municipalities may impose reasonable conditions including owner occupancy, parking, and size limits. Many towns have adopted varying local conditions. The law was strengthened in 2024 to limit municipal restrictions.
Full ADU Regulations Summary for New Hampshire
| ADUs Allowed | Yes |
| Statewide ADU Law | Yes |
| Maximum ADU Size | 800 sq ft |
| Owner Occupancy Required | Yes |
| Parking Required | Yes |
| Minimum Setback | Set locally |
| Permitting Timeline | Varies by municipality |
| Impact Fees | Varies by municipality |
| Long-Term Rental Allowed | Yes |
| Short-Term Rental (Airbnb) Allowed | Yes |
| Ease of Building | Moderate |
ADU Regulations by City in New Hampshire
ADU rules can vary by city even within the same state. While New Hampshire's statewide law sets minimum standards, some cities have additional local provisions. Below are ADU details for 3 cities in New Hampshire.
Manchester
ADUs allowed per state law. Manchester permits attached and detached ADUs with owner occupancy. Maximum 800 sq ft.
Nashua
ADUs permitted in residential zones. Nashua has moderate ADU restrictions within state law framework.
Concord
ADUs allowed with owner-occupancy requirement. Concord has seen moderate ADU construction.
How New Hampshire Compares to Other States
Below is a comparison of New Hampshire with five states that have similar ADU-friendliness scores. This comparison helps illustrate where New Hampshire stands nationally.
| State | Score | Statewide Law | Parking Req? | Owner Occ? | Ease |
|---|---|---|---|---|---|
| New Hampshire (NH) | 55 | Yes | Yes | Yes | Moderate |
| New Mexico (NM) | 55 | No | No | No | Moderate |
| Utah (UT) | 50 | Yes | Yes | Yes | Moderate |
| Rhode Island (RI) | 63 | Yes | No | Yes | Moderate |
| Alaska (AK) | 45 | No | Yes | No | Moderate |
| New Jersey (NJ) | 66 | Yes | No | Yes | Moderate |
Frequently Asked Questions About ADUs in New Hampshire
Can I build an ADU in New Hampshire?
Yes, ADUs are allowed in New Hampshire. New Hampshire has a statewide ADU law that requires local jurisdictions to permit ADUs on residential lots. This means your city cannot outright ban ADUs. The ease of building is rated "Moderate" with a friendliness score of 55/100.
Do I need to live on the property to have an ADU in New Hampshire?
Yes, New Hampshire generally requires owner occupancy — the property owner must live either in the main house or the ADU. This means you cannot rent out both units simultaneously.
How big can an ADU be in New Hampshire?
The state maximum ADU size in New Hampshire is 800 square feet. Local jurisdictions may set lower limits. Some cities also limit ADU size to a percentage of the primary dwelling (e.g., 50%).
Do I need extra parking for an ADU in New Hampshire?
New Hampshire may require additional off-street parking for ADUs. The specific number of spaces depends on your local jurisdiction. This can be a significant barrier if your lot has limited space for parking.
Can I rent out my ADU in New Hampshire?
Yes, long-term rentals of ADUs are allowed in New Hampshire. Short-term rentals (like Airbnb) are also generally permitted, though your city may have separate short-term rental regulations.
How long does it take to get an ADU permit in New Hampshire?
The permitting timeline in New Hampshire is: Varies by municipality. The statewide law sets maximum review periods that cities must comply with. Actual timelines can be affected by plan review backlogs, inspection scheduling, and the complexity of your project. Pre-approved ADU plans, where available, can significantly speed up the process.
Check ADU Rules for Your City
Use our ADU regulations lookup tool to find the specific rules for your city in New Hampshire, or browse all 50 states to compare ADU regulations across the country. Remember that local rules may be more specific than state-level regulations.