ADU Regulations in New Hampshire: The Complete Guide

With its picturesque fall leaves and charming small towns, New Hampshire lives up to its fame boasting both beauty and popularity. What better way to enjoy the whimsical New England life than from the comfort of a luxuriously designed, modular ADU? These versions of tiny homes are taking the housing market by storm with their practicality and versatility. Accessory Dwelling Units are popular for multiple reasons, and we here at Psy Homes think they’re pretty great!

ADUs are the ideal solution for the close by space for your elderly parents to live in independently, or to earn some extra income by converting it into an Airbnb. These compact, yet fully functional homes fit within your home lot, while opening up a whole world of possibilities.

The only thing that is not fun about getting from step one to enjoying your brand-new ADU? All the regulations and restrictions vary from state to state. That’s why we have gathered all the relevant, important information for you, so all you have to do is sit back and relax. Whether you’re a New Hampshire homeowner interested in having an extra dwelling space for your aging parents, or someone curious about how to earn some income by renting out that extra space, this is the article for you.

Are ADUs Allowed in New Hampshire?

Get ready for extremely exciting news: Yes! Effective July 2025, New Hampshire is now an ADU-friendly state! Any municipality with a zoning ordinance must allow one ADU per single-family lot by right. Critically, that one ADU can be attached or detached. If a town’s ordinance is silent, an ADU is still permitted as an accessory use with only the building permit(s) required. This means that no matter where you live, you should be able to build an ADU in New Hampshire! Of course, size restrictions and other regulations can vary by county and town, which we’ll dive into more.

This new law means homeowners have new possibilities available to them like never before. With lenient regulations and limited restrictions from local municipalities, New Hampshire is ready to embrace the world of ADUs. Ready to take the first step in owning your very own modular accessory dwelling unit? Contact us today, and we’ll get you started!

What Is Considered An ADU in New Hampshire?

The New Hampshire Municipal Association defines an ADU as, “a residential living unit that is located on a lot containing a single-family dwelling that provides independent living facilities for one or more persons, including provisions for sleeping, eating, cooking, and sanitation, on the same parcel of land as the principal dwelling unit it accompanies. Accessory dwelling units may be constructed at the same time as the principal dwelling unit.”

Can Park Model Homes Be Used As ADUs?

Usually no, unless they are built/converted to meet residential building code and all local requirements. New Hampshire law treats ADUs as dwelling units, not RVs. A park model typically doesn’t meet the residential code out of the box; you’d need a permanent foundation and full code compliance to be considered a lawful ADU.

However, there are exceptions to this rule, and you can always apply for a special use/conditional permit which may allow a park model home. When in doubt, ask your local building official up front. And don’t forget, there are still many uses for a park model home, even if you can’t use it as an ADU.

Can Log Cabins Be Used As An ADU?

Yes, some log cabins would fit within the 950 sq. foot size requirement that New Hampshire has laid out. This would require a more rural parcel of land, but with the right property, a log cabin could be the perfect ADU solution for you. Several of the models from Psy Homes could be a cozy and comfortable getaway for your ADU guests.

Can Modern Cabins Be Used As An ADU?

Yes. Just like log cabins, modern cabins follow the same logic. If you meet the size requirements, setbacks, utilities, and all the permits, you will be good to go. The state minimum size limit towns can impose is 750 sq ft and the default cap is 950 sq ft unless the municipality authorizes more. Many towns do allow larger square footage when you ask the planning staff.

What is the Difference Between a Prefab ADU & a Modular ADU?

This is a great question, and one commonly confused. The difference is pretty minimal and comes down to simple differences in manufacturing and set up.

Pre-fab ADUs will be fully constructed in a factory and then delivered and set up in one straight process.

On the other hand, modular ADUs are constructed in sections in a factory, then assembled on the building site which allows for final adjustments and necessary changes. When it comes to regulations and permits, New Hampshire doesn’t differentiate between the two.

What is the Minimum Size for an Accessory Dwelling Unit in New Hampshire?

This can depend on where you live. Towns may set size limits, but they cannot require smaller than 750 sq ft for an ADU. Owners may choose to build smaller if the local ordinance allows.

What is the Maximum Size for an Accessory Dwelling Unit?

As of this year, the new requirement in New Hampshire is 950 square feet, which allows for large and comfortable ADUs, while still maintaining the integrity of an ADU’s purpose to support the main dwelling space.

Can My ADU be Bigger Than My House?

No, ADUs were never designed to exceed the size of the primary dwelling, only enhance and support it.  This means your ADU can not be larger than your existing house. You can choose to live in either one, but the ADU must remain smaller than the main dwelling space, and still fit within the maximum 950 square feet restriction.

How Close To My House Can I Build An ADU?

An ADU must meet the same dimensional rules (setbacks, lot coverage, etc.,) as a single-family home in that district and towns can’t impose stricter setbacks just because it’s an ADU. Typically, this setback is around 10 feet for a rear setback and 5 feet for a side setback.

Do You Need A Permit For An ADU in New Hampshire?

Yes. With the 2025 law, one ADU is permitted by right, but you still need the building permits and inspections (plus electrical/plumbing/HVAC permits as applicable). If a town’s ordinance is silent, the ADU is still deemed a permitted accessory use with only the building permit required.

Are There Any Incentives or Grants for ADUs in New Hampshire?

Unfortunately, there’s no current standing statewide homeowner grant specific to ADUs. New Hampshire Housing has published program models that suggest pre-approved plans, financing ideas, amnesty/loans from other states, etc. that localities could adopt, but those are not statewide subsidies. However, you should definitely watch your town/city as some may pilot incentives or fee reductions soon based on these new regulations.

Are Psy Homes’s ADUs Built to Code?

Absolutely. Not a single ADU leaves the Psy Homes lot without being thoroughly inspected and built to match and exceed your local building codes. Our skilled team of builders and designers don’t just have beauty and functionality in mind, they also prioritize your safety and compliance with local codes.

Can an ADU Have Multiple Bedrooms and Bathrooms?

Definitely.

In New Hampshire, the new laws passed specify that towns can’t limit ADUs to only one bedroom. However, they can limit it to two bedrooms if they choose. Either way, a multi-bedroom ADU is an exciting investment and opens up more space and privacy options. Psy Homes offers several popular options for one or two bedroom options, depending on your specific needs. Choose the model that is tailored to your ideal ADU dreams!

Are ADUs A Good Investment?

Yes!

Accessory dwelling units are a great choice of investment, particularly if you are able to rent out the space. ADU homeowners report a relatively quick return on investment (ROI) plus they can increase your property value. Not to mention they offer affordable housing options for you and your loved ones. Curious to learn more? Call one of our knowledgeable sales representatives and they will walk you through the process, and offer advice on the best decision to make.

ADU Regulations in New Hampshire by County

Belknap County	Department Directory
Carroll County	Zoning Ordinances
Cheshire County	Zoning Atlas
Coös County	Zoning Board of Adjustment
Grafton County	Department Directory
Hillsborough County	Zoning Board of Adjustment
Merrimack County	Zoning Board
Rockingham County	Planning Commission
Strafford County	Planning and Zoning Office
Sullivan County	Planning and Zoning

Does Belknap County, New Hampshire, Allow ADUs?

Yes, but it is via its towns/cities. Belknap County itself doesn’t regulate ADUs; instead, places like Laconia, Belmont, Gilford, Meredith, and Tilton each apply the state requirements.

Towns can require up to one extra off-street space and can set ADU size caps. All these regulations must adhere to the state requiremetns. If you live in Belknap County, the best place to start is with your local planning and zoning department to get all your zoning questions answered. Then you can move on to the building department for permit guidance.

Does Carroll County, New Hampshire, Allow ADUs?

Yes, but like other New Hampshire counties, it is done at the municipal level. Carroll County doesn’t have countywide zoning. Check towns like Wolfeboro, Conway, Moultonborough, Tuftonboro for specific zoning ordiances. The 2025 state law guarantees one ADU by right (attached or detached) which means your town can’t pile on ADU-specific setbacks or limit you to one bedroom, but it can set size caps, and require up to one parking space and owner-occupancy. Contact your town planning/zoning for the ADU section and your building department for permits/inspections and water/sewer sign-off.

Does Cheshire County, New Hampshire, Allow ADUs?

It sure does! However, here again, it’s through the municipalities. State law controls the minimums which dictates one ADU by right, whether attached or detached and standard district setbacks/coverage also apply. Towns must follow these but at the county level, there is really very little specifics. To move ahead, you will need to contact your local planning and zoning board and ask about your town’s specific requirements.

Does Coos County, New Hampshire, Allow ADUs?

Yes, and here county government actually matters. Coös County’s Planning Board has zoning for 23 unincorporated places and then the towns/cities regulate themselves as usual. If you’re in an unincorporated place, review Coös County’s zoning and then confirm permits with the county. Since this is a large part of the county, you may find yourself reaching out to the county for assistance.

 If you’re in a town/city like Berlin, Lancaster, or Gorham, the municipal ordinance applies under the statewide one ADU by right (attached or detached) rule. Start with the Coös County Planning Board for unincorporated areas and the town planning/building offices elsewhere.

Does Grafton County, New Hampshire, Allow ADUs?

Yes, via the towns/cities. The state floor guarantees one by-right ADU, which local towns are required to follow. Because zoning and planning is handled by the local departments, it is more helpful to go straight to them instead of the county department. Go to your Planning/Zoning for ordinance text (look under “Accessory Dwelling Unit”) and your Building/Code office for permits and utility sign-offs. NHMA’s 2025 memo and NHHFA guide also explain the statewide limits on what towns can and can’t require.

Does Hillsborough County, New Hampshire, Allow ADUs?

Different New Hampshire county but the same story. Yes, ADUs are allowed, but the specific regulations will be found at the local level. The county doesn’t regulate ADUs apart from following the state laws. Major communities in this county include Manchester, Nashua, Bedford, Merrimack, and Goffstown. These towns can’t add ADU-only setbacks or limit to one bedroom but they can set a size cap (not below 750 sq ft; default cap 950 sq ft) and require up to one parking space and owner-occupancy. Take the next step by checking your city/town planning department for the ADU section and the building department for permit submittals.

Does Merrimack County, New Hampshire, Allow ADUs?

They sure are! For Concord, Bow, Hooksett, Hopkinton, Pembroke and beyond, the same statewide baseline applies in this county. One ADU, whether attached or detached, is allowed by right. After the municipalities meet the state requirements,they are allowed to impose a few more minor restrictions. This means that to find out specific information, you will need to start with your town’s planning and zoning department, instead of the county office. NHMA’s 2025 memo and NHHFA guide also explain the statewide limits on what towns can and can’t require.

Does Rockingham County, New Hampshire, Allow ADUs?

Yes but it is via municipalities. Rockingham towns all follow the one ADU by right mandate (attached or detached). Expect typical plan review for setbacks/lot coverage, structural and life-safety code, and adequate water/sewer. To confirm local details like a size cap and owner-occupancy requirements, you will need to contact your local planning and zoning department.

Does Strafford County, New Hampshire, Allow ADUs?

It sure does, but it takes place through municipalities. Cities/towns like Dover, Rochester, Durham, Somersworth must allow one ADU by right (attached or detached). Towns can keep standard residential setbacks and coverage, set a 750 sq ft minimum-allowable size and cap it at 950 square feet, unless they want to allow more, and may require owner-occupancy and up to one parking space. Go to your local planning and zoning department to find out the most accurate, up-to-date information.

Does Sullivan County, New Hampshire, Allow ADUs?

Yes, by way of the local municipalities. All towns like Claremont, Newport, Charlestown, Sunapee follow the state regulations which allow one ADU by right when they follow standard setbacks and proof of adequate water/sewer. Following this, towns can make minor additional restrictions, but there is little help at the county level. The next best thing to do is call up your town’s building department to find out about permits, or contact the zoning commission to find out more about zoning specifics. NHMA’s 2025 memo and NHHFA guide also explain the statewide limits on what towns can and can’t require.

Accessory Dwelling Unit Requirements By Municipality

Manchester	Zoning Ordinances
Nashua	Online Ordinances
Concord	Code of Ordinances
Derry	Ordinances
Salem	Codes and Regulations

Does Manchester, New Hampshire, Allow ADUs?

Yes. Manchester’s zoning sets a max 900 sq ft, max 2 bedrooms, and requires owner-occupancy memorialized by a recorded deed restriction when you get the CO. You’ll follow normal rules regarding setbacks and height like you would for a single family house plus pull the correct building/mechanical/electrical/plumbing permits. Under state law (2025) you can do an attached or detached ADU by right. Start with Planning & Zoning for ordinance interpretation and Building for submittals and permit questions.

Does Nashua, New Hampshire, Allow ADUs?

It sure does. Nashua’s code allows one ADU per lot, which must be smaller than the primary dwelling and caps it at 750 sq ft. Nashua also emphasizes maintaining single-family appearance Historically, Nashua treated these as internal/attached units but after HB 577 (2025), one ADU, attached or detached is allowed by right, so detached is now allowed even if local text still lags. Confirm size/parking and any owner-occupancy paperwork with Planning; then apply with Building Safety for permits.

Does Concord, New Hampshire, Allow ADUs?

Yes!  Concord’s past amendments limited ADUs to attached with a common wall and an interior door and no more than 2 bedrooms, plus compliance with standard lot size/setbacks and owner-occupancy proof. However, HB 577 (effective July,2025) now enables one attached or detached ADU by right statewide so while local dimensional and design rules still apply, the “attached-only” clause no longer blocks a detached unit. Contact Concord Planning for the next step forward.

Does Derry, New Hampshire, Allow ADUs?

Definitely. Derry’s ordinance defines an ADU as within or attached to a single-family dwelling, typically 1–2 bedrooms, and subject to IRC room-size minimums. Practically, you’ll still meet the district’s normal setback restrictions and get standard building permits. After new legislation this year, one ADU per lot is allowed by right so detached ADUs are now permissible despite “attached” language in older code PDFs. You can expect the town to update the text soon. For more questions, check with Planning/Zoning for the updated ADU regulations in Derry.

Does Salem, New Hampshire, Allow ADUs?

It sure does! Salem explicitly allows one “accessory apartment” with max 2 bedrooms and max 950 sq ft, requires the owner to occupy one unit, an interior door between units, and off-street parking. Historically this meant inside the single-family dwelling; under HB 577 (2025) you now have by-right attached or detached statewide. Salem will still apply its size/bedroom/parking rules where consistent with state law until its ordinance is updated. Start with the Planning Division for ordinance guidance and they will direct you to the next step.

Tiny Homes & ADU Rules by State: How Do They Compare?

If you find yourself confused with the overwhelming amount of regulations and questions around what is and isn’t allowed, you are not alone. Whether it’s tiny homes or ADUs, there is an onslaught of information. We did the work for you, and gathered all the information into helpful sections. Check out our tiny home regulations by each state. Simple click on the state you are interested in and find out all the regulations.  Or do the exact same thing with our ADU regulations chart! No matter where you live, Psy Homes wants to make it possible for you to embrace a new way of living.

Searching for an ADU Builder Serving New Hampshire?

Ready to take the next step? Next in the process is searching for a trustworthy ADU builder that will actually make your dreams a reality. Psy Homes is pleased to offer you all experience and skills that we have been honing for years in this industry. Moving ahead is as simple as contacting us and talking to a sales representative or requesting a free quote.

We know that these days, it can be hard to choose who to work with to make your dreams become a reality. That’s why we promise transparent pricing, a commitment to the end, and an excellent work ethic. Choose Psy Homes today and watch your vision of the ideal ADU unfold from start to finish.

Conclusion…

As you can see, ADU laws can be a bit challenging to understand, even in a state that allows them by right. However, at Psy Homes, we have the ability to help you find the ADU home of your dreams. So when you are ready to DWELL BEYOND THE ORDINARY, contact us!