Accessory Structures in Nashua, NH (2026)
5 verified accessory structures rules for Nashua, New Hampshire, sourced directly from the municipal code and official government pages.
Verified from official government sources
ADU Rules
Effective July 1, 2025, NH RSA 674:71-:73 (as amended by HB 577) requires Nashua and every NH municipality to allow one accessory dwelling unit (attached or detached) by-right on every single-family lot, with no minimum size below 750 sq ft and a default maximum of 950 sq ft. Nashua's pre-2025 Sec. 190-32 capped ADUs at 30 percent of the principal dwelling or 700 sq ft, required owner occupancy, and limited rental to family — those provisions are now preempted by state law to the extent they conflict. Existing detached structures (garages, barns) may be converted regardless of current setback nonconformity.
Nashua Accessory Dwelling Unit Rules
Few RestrictionsShed Rules
Nashua does not require a building permit for a shed of 200 sq ft or less, but a Land Use Permit (zoning) is required from the Nashua Department of Building Safety regardless of shed size to confirm setback compliance under Sec. 190-16 and Sec. 190-31 (accessory buildings). A plot plan showing shed location must be submitted. Sheds in residential zones (R-40, R-30, R-18, R-9, R-A, R-B) typically must meet a 4 ft side/rear accessory setback and sit behind the principal building's front facade.
Nashua Shed Rules
Few RestrictionsGarage Conversions
Converting a Nashua garage to habitable space requires a building permit and electrical permit from the Department of Building Safety under the NH State Building Code (IRC change of occupancy from U to R-3). If the conversion adds a kitchen and separate entrance, the result is an Accessory Dwelling Unit governed by NH RSA 674:71-:73 (HB 577, 7/1/2025) — Nashua must permit the conversion by-right even where the existing garage does not meet current setbacks, and the ADU may be up to 750-950 sq ft.
Nashua Garage Conversion
Few RestrictionsCarport Rules
Nashua Land Use Code Sec. 190-31 (Accessory Buildings) treats unattached carports as detached accessory structures subject to a typical 4 ft side/rear setback, behind-the-front-facade rule, and the underlying district's dimensional standards in Sec. 190-16. Construction requires a building permit through the Nashua Department of Building Safety under the NH State Building Code, with engineered anchorage for the 115 mph basic wind speed in Hillsborough County. Attached carports follow the principal building's setbacks.
Nashua Carport Rules
Few RestrictionsTiny Homes
NH RSA 674:74 defines tiny houses as small structures intended for year-round occupancy that meet the NH State Building Code and may be on a permanent foundation or chassis. Where Nashua permits detached ADUs under RSA 674:73 (it must, as of 7/1/2025), it must permit a single tiny house as a detached ADU — but a lot may have either an ADU or a tiny house, not both. Tiny houses must include facilities for sleeping, eating, cooking, and sanitation and meet all single-family building, fire, safety, and utility codes. Park-model RVs and tiny houses on wheels not meeting the State Building Code are not permitted as permanent dwellings.
Nashua Tiny Home Rules
Some RestrictionsLooking for Hillsborough County county-wide rules?
County ordinances apply to unincorporated areas and may supplement Nashua city rules.
Accessory Structures in Hillsborough County →