Can I build a duplex on a single-family lot in New Hampshire?

There is no statewide duplex mandate; New Hampshire has no county zoning and each of its roughly 234 municipalities sets its own permitted-use rules under RSA 674, so duplex allowances vary widely by town. New Hampshire's clearest statewide density floor is its accessory dwelling unit law, not a duplex law.

Are accessory dwelling units legal in New Hampshire?

Yes, statewide. RSA 674:71 through 674:73 requires every municipality to allow at least one accessory dwelling unit by right on a lot with a single-family home, including conversions of existing structures like detached garages even if they don't meet current setback rules. A second ADU may be allowed by right or by conditional use permit, depending on the town.

How do I look up zoning for a parcel in New Hampshire?

Statewide parcel geometry is available through NH GRANIT and the NH Geodata Portal, but because New Hampshire has no county or state zoning layer, you need the specific town or city's own zoning map — many of which are only available directly from the municipal planning office rather than through a unified state GIS system.

Is New Hampshire a home-rule state for zoning?

Not formally — New Hampshire is generally considered a Dillon's Rule state, and all municipal zoning power derives from the state enabling statute, RSA 674. In practice, however, zoning is highly decentralized: there is no state zoning agency and no county-level zoning at all, so each town or city exercises its RSA 674 authority independently.

New Hampshire · state zoning reference · Parcel data · lookup only

New Hampshire zoning: how it works and what you can build

New Hampshire has no county-level zoning and no state land use agency — all 234 towns and cities zone independently under a single state enabling statute, and a growing statewide ADU-by-right law and workforce-housing mandate are the two biggest recent constraints on that local autonomy.

How zoning works in New Hampshire

New Hampshire is one of the most locally fragmented zoning states in the country. Counties have no zoning authority at all — every one of the state's cities and towns that chooses to zone does so independently under a single enabling statute, RSA 674 ("Local Land Use Planning and Regulation"), and many small towns have no zoning ordinance whatsoever, relying instead on subdivision and site-plan review or nothing at all. There is no statewide land use plan and no state zoning agency; the New Hampshire Office of Planning and Development provides guidance and model ordinances, but adoption and amendment are entirely local, town-meeting-driven decisions in most municipalities.

Within that fragmented system, the state has nonetheless layered in two significant statewide constraints. First, the workforce housing law (RSA 674:58 through 674:61), rooted in the state supreme court's Britton v. Chester decision, requires every municipality to provide "reasonable and realistic" opportunities for workforce housing development, including multifamily and manufactured housing, and gives builders a path to challenge municipalities that don't. Second, the state's accessory dwelling unit statute (RSA 674:71 through 674:73), substantially strengthened by 2022's HB 1291 and refined in subsequent sessions, requires municipalities to allow at least one ADU by right on any lot with a single-family home, permits conversion of existing structures such as detached garages even where they don't meet current setback or lot-coverage standards, and allows a second ADU by right or conditional use.

For developers, the practical takeaway is that New Hampshire zoning diligence is inherently a town-by-town exercise — there is enormous variation between, say, Manchester's urban zoning code and a rural town's minimal one — but the ADU and workforce-housing statutes provide two statewide floors that no local ordinance can zone below.

Who holds the zoning power

Land-use authority in New Hampshire is delegated by statute, not assumed — these are the acts a zoning ordinance in New Hampshire has to trace back to.

Local Land Use Planning and Regulation New Hampshire Revised Statutes Annotated, Chapter 674: Core enabling statute for municipal zoning ordinances, master plans, and land use boards; counties have no zoning role.
Workforce housing law RSA 674:58 through 674:61: Requires municipalities to provide reasonable, realistic opportunities for workforce and multifamily housing.
Accessory dwelling unit law RSA 674:71 through 674:73: Requires at least one ADU by right on single-family lots statewide; strengthened by HB 1291 (2022) and later amendments.

Major cities and their codes

The enabling act sets the ceiling; the municipal code is what a project is actually reviewed against. The 6 largest New Hampshire jurisdictions and the codes they administer:

New Hampshire — municipal zoning codes
City	Zoning code
Manchester	City of Manchester Zoning Ordinance State's largest city, with the highest concentration of multifamily and mixed-use redevelopment activity in New Hampshire.
Nashua	City of Nashua Zoning Ordinance Second-largest city; has explored form-based code elements for its downtown core.
Concord	City of Concord Zoning Ordinance State capital; also exploring form-based code approaches in select districts.
Derry	Town of Derry Zoning Ordinance One of the state's largest towns by population, zoned under RSA 674 like all NH municipalities.
Dover	City of Dover Zoning Ordinance Seacoast-region growth market with active mixed-use downtown redevelopment.
Rochester	City of Rochester Zoning Ordinance Seacoast-adjacent city with comparatively lower land costs than Portsmouth-area markets.

Recent reforms

State-level changes override or preempt what a local ordinance says — these are the New Hampshire reforms that move the numbers on a real site.

2022 Statewide ADU-by-right expansion (HB 1291) Strengthened RSA 674:71-73, requiring municipalities to allow at least one ADU by right, including conversions of nonconforming structures.

Parcel & GIS data

NH GRANIT, the state's GIS clearinghouse hosted at the University of New Hampshire, publishes a statewide parcel mosaic compiled from municipal and county records via the NH Geodata Portal.

Real parcel geometry is already loaded for Derry — see the zoning-by-city section above for a live district-and-parcel lookup there. That is not the same as a cited feasibility report: Chicago is still the only jurisdiction with bulk standards, § citations and a generated massing scheme.

Zoning by city

The statute sets who may zone; the city's own code sets what you can build. One guide per New Hampshire city below, explaining the district codes that appear on its zoning map — 79 district codes across New Hampshire so far.

New Hampshire zoning — common questions

Can I build a duplex on a single-family lot in New Hampshire?: There is no statewide duplex mandate; New Hampshire has no county zoning and each of its roughly 234 municipalities sets its own permitted-use rules under RSA 674, so duplex allowances vary widely by town. New Hampshire's clearest statewide density floor is its accessory dwelling unit law, not a duplex law.
Are accessory dwelling units legal in New Hampshire?: Yes, statewide. RSA 674:71 through 674:73 requires every municipality to allow at least one accessory dwelling unit by right on a lot with a single-family home, including conversions of existing structures like detached garages even if they don't meet current setback rules. A second ADU may be allowed by right or by conditional use permit, depending on the town.
How do I look up zoning for a parcel in New Hampshire?: Statewide parcel geometry is available through NH GRANIT and the NH Geodata Portal, but because New Hampshire has no county or state zoning layer, you need the specific town or city's own zoning map — many of which are only available directly from the municipal planning office rather than through a unified state GIS system.
Is New Hampshire a home-rule state for zoning?: Not formally — New Hampshire is generally considered a Dillon's Rule state, and all municipal zoning power derives from the state enabling statute, RSA 674. In practice, however, zoning is highly decentralized: there is no state zoning agency and no county-level zoning at all, so each town or city exercises its RSA 674 authority independently.

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The parcel layer lands in the order demand does. Illinois went first because that's where the deals were; the next state is decided by who tells us what they're trying to underwrite. Tell us where you're building and what you wanted to run — you'll hear from us when New Hampshire opens, and sooner if we need a test parcel.

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Want to see the finished shape of this work? Illinois is live at parcel level — Illinois zoning and the 53-district Chicago reference.

New Hampshire zoning summaries on this page are provided for information, not legal advice. Confirm every project against the current adopted code for the jurisdiction and the statute as amended.