Residential permit rules in New Hampshire
Representative cities: Manchester, Nashua. Covers 20 common home projects.
| Project | Permit? | Authority | Typical fee | Timeline | Go / No-Go | Key notes |
|---|---|---|---|---|---|---|
| 🏠 Accessory Dwelling Unit (ADU) | Permit required | city | — | — | Generally allowed | New Hampshire has no statewide by-right ADU law; whether an ADU is allowed depends on local zoning. The structure itself requires a building permit under the state residential code regardless of town ordinance. Exempt: No statewide ADU mandate; an ADU is a dwelling unit and requires a building permit. |
| 🪵 Deck / Porch | Conditional | city | — | — | Generally allowed | New Hampshire footings must extend to frost depth (commonly 48 in). Even exempt low decks must meet zoning setbacks. Verify the threshold with your local building department — some towns permit any attached deck. Exempt: Decks ≤30 in above adjacent grade and (in most towns) ≤200 sq ft are exempt from a building permit. |
| 🧱 Fence / Wall | Conditional | city | — | — | Generally allowed | Pool-enclosure fences must meet the adopted pool/spa code barrier requirements. Zoning (height, sight triangles, corner lots) is separate from the building-permit exemption. Exempt: Fences not over 7 ft in height are exempt from a building permit under IRC R105.2. |
| 🛖 Shed / Outbuilding | Conditional | city | — | — | Generally allowed | Even exempt sheds must meet property setbacks and lot-coverage rules. Adding utilities (electrical/plumbing) always requires separate trade permits. Exempt: One-story detached accessory structures ≤120 sq ft (IRC R105.2) are commonly exempt from a building permit; observed local thresholds range 100–200 sq ft. |
| 🪜 Basement Finish | Permit required | city | — | — | Generally allowed | Basement finishes require egress windows for bedrooms, plus electrical, HVAC, and any structural permits; vapor-barrier/insulation rules apply under the NH energy code. Exempt: Cosmetic finishing (paint, flooring) is exempt. |
| 🚗 Garage / Carport | Permit required | city | — | — | Generally allowed | Setbacks, lot coverage, and energy-code compliance are reviewed. Repair of an existing garage may be exempt. Exempt: New detached structures over the local accessory-exemption size require a permit. |
| ☀️ Rooftop Solar PV | Permit required | city | — | — | Generally allowed | Structural review accounts for NH ground-snow loads (40–100+ psf by town) and 48-in frost-depth footings for ground mounts. Exempt: No size exemption; rooftop PV always permitted. |
| 🌡️ HVAC Replacement | Conditional | city | — | — | Generally allowed | NH requires licensed mechanical/electrical contractors for the work; equipment must meet current energy-code efficiency rules. Exempt: In-kind replacement in the exact location may be treated as repair; verify with the local official. |
| 🍳 Kitchen Remodel | Conditional | city | — | — | Generally allowed | NH energy code is triggered on remodels (insulation, window U-factor, HVAC). Verify scope with the local building department. Exempt: Cabinet/countertop swap in the same layout is exempt. |
| 🛁 Bathroom Remodel | Conditional | city | — | — | Generally allowed | Exterior ventilation is required. Licensed plumbers must pull the plumbing permit. Exempt: Fixture-for-fixture swap in place is often exempt. |
| 🏗️ Room Addition | Permit required | city | — | — | Generally allowed | Plan review covers setbacks, lot coverage, energy code, and structural/frost-depth footings. Exempt: No exemption — any new conditioned footprint requires a permit. |
| 🪟 Window / Door Replacement | Conditional | city | — | — | Generally allowed | Replacement products should meet energy-code U-factor when the code is triggered. Licensed contractors pull trade permits. Exempt: Same-size, in-kind replacement is generally exempt. |
| 🏘️ Roof Replacement | Conditional | city | — | — | Generally allowed | Local practice varies — e.g., Hampton Falls exempts in-kind roofing, while Plaistow requires a permit for roof replacement. Confirm with your town. Exempt: Same-footprint, in-kind re-roof is often exempt/over-the-counter. |
| 🅿️ Driveway / Parking Pad | Conditional | city | — | — | Generally allowed | A separate driveway/right-of-way permit is usually needed to cut the curb or connect to the street. Exempt: Replacing a driveway in the same footprint (no new curb cut) is generally exempt. |
| 🏊 Swimming Pool / Spa | Permit required | city | — | — | Generally allowed | Barrier/ fencing and electrical bonding are reviewed; pool-barrier requirements apply in every jurisdiction. Exempt: No exemption — all pools/spas require a permit (NH adopts the 2021 ISPSC). |
| 🧱 Retaining Wall | Conditional | city | — | — | Generally allowed | Local towns may set a stricter height (e.g., Plaistow lists hardscaping under 6 ft as exempt from a building permit). Verify with your building department. Exempt: Retaining walls not over 4 ft (measured bottom of footing to top) are exempt. |
| 💥 Demolition / Teardown | Permit required | city | Demolition permit fee set by the issuing authority; verify locally. | — | Generally allowed | A full teardown or major strip-out requires a demolition (building) permit. Demolition permits commonly require proof of utility disconnects (water, gas, electric, sewer) and may require asbestos/lead-paint clearance for pre-1978 homes before work begins. Verify the issuing authority for your specific property. |
| 🚰 Septic System | Permit required | state | Septic permit/approval fee set by NH DES; residential system application fees are based on design flow. | — | Generally allowed | New or replacement onsite wastewater (septic) systems require an Approval for Septic System Construction from the New Hampshire Department of Environmental Services (NH DES Subsurface Systems Bureau), followed by an Approval for Operation before use. A soil/perc evaluation and engineered design are required; licensed designers prepare the plans and licensed installers perform the work, and the system is inspected by a NH DES regional inspector before backfill. |
| 🔌 EV Charger | Conditional | city | Electrical permit; fee set by the issuing authority. | — | Generally allowed | A home EV charging station (240V branch circuit + wall-mounted EVSE) requires an electrical permit and must meet the NEC (Article 625). Many jurisdictions fast-track residential EVSE. A load calculation and possible service upgrade are reviewed. |
| ⚡ Standby Generator | Conditional | city | Mechanical/electrical permit; fee set by the issuing authority. | — | Generally allowed | A permanently installed standby generator requires mechanical and electrical permits (transfer switch, fuel gas/propane line). Setback, carbon-monoxide ventilation, and noise rules apply; some HOAs restrict generator placement. |
Frequently asked questions
Do I need a building permit for home projects in New Hampshire?
Most structural, electrical, plumbing, and mechanical work does. The project table above shows New Hampshire-specific permit requirements for 20 common home projects. Always confirm with the local building department before starting.
Who issues building permits in New Hampshire?
New Hampshire permit authorities are typically city or county building departments. Use the county permit authority lookup to find the exact office for your property.
Which home projects are exempt from permits in New Hampshire?
Common baseline exemptions apply widely: detached sheds ≤120 sq ft, fences ≤6–7 ft, decks ≤30 in above grade, same-footprint re-roofs, and in-kind window/door swaps. New Hampshire or your city may amend these — verify locally.
How much does a permit cost in New Hampshire?
Permit fees are set by each city or county and scale with project valuation; there is no single New Hampshire statewide fee. Open the official authority link on this page for the local fee schedule.