The New Hampshire state building code, codified under RSA 155-A, sets minimum standards for how buildings are designed, built, renovated, and maintained anywhere in the state. It adopts the 2021 editions of the International Building Code, International Residential Code, International Existing Building Code, International Plumbing Code, International Mechanical Code, and International Swimming Pool and Spa Code, along with the 2018 International Energy Conservation Code and the 2023 National Electrical Code.1New Hampshire Division of Fire Safety. New Hampshire Code 155-A – New Hampshire Building Code The code is technically in force everywhere, but who checks your work depends on whether your town has adopted local enforcement.
Which Model Codes Apply
RSA 155-A:1 adopts eight model codes by reference. The IBC governs commercial buildings and larger multi-family structures. The IRC covers single-family homes, duplexes, and townhouses up to three stories. The IEBC applies to renovations, alterations, and repairs. The IPC and IMC govern plumbing and mechanical systems. The IECC sets energy performance standards. The pool and spa code regulates residential and commercial pools. The National Electrical Code, published by NFPA, governs all electrical work.1New Hampshire Division of Fire Safety. New Hampshire Code 155-A – New Hampshire Building Code
Two edition details matter. The energy code is still the 2018 IECC with state amendments while the other codes have moved to 2021.2NH Department of Energy. Energy Codes And even though New Hampshire has adopted the 2023 NEC, arc-fault circuit interrupter enforcement is capped at what the 2014 NEC required.3New Hampshire General Court. New Hampshire Revised Statutes Section 155-A:2 – State Building Code
When a new edition takes effect, RSA 155-A:2 gives applicants a six-month window in which they can choose either the old code or the new one, but they cannot mix provisions from both.3New Hampshire General Court. New Hampshire Revised Statutes Section 155-A:2 – State Building Code The code in effect when your permit application is received governs the whole life of that permit, so a mid-project update doesn’t shift your requirements.
Who Enforces the Code Where You Are
Every municipality is covered by the state code, but enforcement depends on whether the town has opted in under RSA 674:51.4New Hampshire General Court. New Hampshire Revised Statutes Section 674:51 – Power to Adopt Building Codes Towns and cities that have adopted enforcement appoint a building official who reviews plans, issues permits, conducts inspections, and issues certificates of occupancy.
In municipalities without a local enforcement mechanism, the state fire marshal has authority to enforce the code and can set permit fees. Contractors doing non-residential work in those towns must notify the fire marshal about the type of construction before starting. Single-family and two-family dwellings are exempt from that notification, so residential enforcement in small towns without a building department is often thin in practice.3New Hampshire General Court. New Hampshire Revised Statutes Section 155-A:2 – State Building Code
Thin enforcement is not permission to ignore the code. The obligation to comply is the same whether or not anyone inspects. A home built without inspections can still create problems at sale, at insurance underwriting, or after an injury on the property.
What Towns Can and Cannot Change
Local governments cannot weaken the state code, and they face tight limits on strengthening it. Under RSA 155-A:3, no municipality may amend the technical requirements of the state code unless the state code has fallen more than two editions behind the published model codes. Even then, a local amendment cannot be more or less stringent than the current model code, and the State Building Code Review Board must confirm the amendment before it can be enforced.5New Hampshire General Court. New Hampshire Revised Statutes Section 155-A:3 – Local Enforcement The state code functions as both floor and ceiling on technical construction standards.
What towns do control: fee schedules, permit procedures, whether to require certificates of occupancy, and everything on the zoning side, including setbacks, density, and historic district rules.1New Hampshire Division of Fire Safety. New Hampshire Code 155-A – New Hampshire Building Code Zoning is separate from the building code and is where most locally distinctive rules actually live.
Permits and Inspections
Before construction, renovation, or structural modification, you need a building permit from your local building department, or in some cases from the state fire marshal’s office where a town has no local enforcement. Applications generally require construction plans showing floor layouts, doors, and windows; elevation drawings; structural details for load-bearing elements like beams, headers, and joists; and a plot plan showing where the building sits relative to property lines and setbacks. If property lines cannot be verified, a certified survey may be required.
The building official reviews the plans for compliance with structural, energy, plumbing, and electrical standards. Deficient plans have to be revised and resubmitted. Projects that touch historic properties, wetlands, or other environmental constraints may need review by additional state agencies.
Once the permit issues, work can proceed but inspections happen at set stages. Typical checkpoints are foundation, framing, electrical and plumbing rough-in, mechanical systems, and a final inspection before occupancy. Inspectors can issue correction notices requiring a fix before the next phase. Fees vary town by town.5New Hampshire General Court. New Hampshire Revised Statutes Section 155-A:3 – Local Enforcement
Residential energy compliance is documented on form EC-1, submitted as part of the permit package.2NH Department of Energy. Energy Codes Snow load calculations follow site-specific values from a U.S. Army Corps of Engineers study covering every municipality in the state, not generic map values.6Structural Engineers of New Hampshire. New Hampshire State Building Code
Doing Your Own Work as a Homeowner
New Hampshire lets homeowners perform their own construction and electrical work on a single-family residence, provided it is the owner’s primary residence and the owner personally occupies it. The authority sits in RSA 319-C:15 for electrical work and RSA 153:36 for other building work. The exemption does not extend to rental properties, second homes, or work performed on your behalf by an unlicensed friend or family member. All work still has to comply with the state code, and you still pull the appropriate permits and pass inspections where the municipality requires them. Some towns require a pre-permit meeting before issuing a permit to an owner-builder.
Residential, Commercial, and Industrial Differences
Single-family homes, duplexes, and townhouses up to three stories fall under the IRC. Commercial buildings — offices, retail, hotels, restaurants — fall under the IBC and face stricter fire protection because of higher occupancy loads. Sprinkler systems, fire-rated construction, and smoke barriers depend on size, height, and occupancy classification. Accessibility follows the federal Americans with Disabilities Act baseline plus New Hampshire’s barrier-free design requirements under RSA 275-C.7New Hampshire General Court. New Hampshire Revised Statutes Section 275-C:15 – Powers
Industrial facilities like manufacturing plants and warehouses layer additional fire suppression and environmental permitting on top of the IBC. Projects involving hazardous materials or air emissions typically require permits from the Department of Environmental Services alongside the building permit.
Accessory Dwelling Units
New Hampshire law strongly favors ADUs and preempts most local restrictions. Under RSA 674:72, every municipality with zoning must allow at least one ADU, attached or detached, as a matter of right on any lot that permits a single-family home. If a zoning ordinance is silent on ADUs, one is automatically permitted as an accessory use with only a standard building permit required.8New Hampshire General Court. New Hampshire Revised Statutes Section 674:72 – Accessory Dwelling Units
Municipalities cannot restrict an ADU’s living space below 750 square feet, and the default maximum is 950 square feet unless the town authorizes more. Extra lot size requirements, additional setbacks, aesthetic review, and design standards beyond those that apply to the main house are all prohibited. The town can require up to one additional parking space, and the owner chooses whether to put it on-site or at a legally dedicated off-site location.8New Hampshire General Court. New Hampshire Revised Statutes Section 674:72 – Accessory Dwelling Units
A town may require that the owner occupy one of the two units but cannot dictate which one, and cannot require any family relationship between occupants. Water and sewage must be adequate, but separate systems are not required and the municipality cannot impose stricter septic standards than the Department of Environmental Services. Selling an ADU as a separate condominium unit is prohibited unless the municipality specifically permits it.8New Hampshire General Court. New Hampshire Revised Statutes Section 674:72 – Accessory Dwelling Units
Renovations and Historic Buildings
Work on existing buildings falls under the 2021 IEBC, which offers a more flexible compliance framework than new-construction rules.1New Hampshire Division of Fire Safety. New Hampshire Code 155-A – New Hampshire Building Code Structural modifications and major system upgrades still have to meet current standards, but the code recognizes that full compliance is not always achievable in older structures.
Historic properties get further flexibility. For buildings listed on or eligible for the National Register of Historic Places, or designated under a state or local preservation program approved by the U.S. Department of the Interior, a registered design professional can file a report identifying which safety features comply, which do not, and how the project achieves equivalent safety without damaging historic character. Original or similar materials and methods are allowed, though asbestos and lead-based paint cannot be reintroduced where the new-construction code would prohibit them. When a code official identifies an unsafe condition, remediation is limited to that specific hazard rather than a full building upgrade. Historic buildings in flood hazard areas are also spared the “substantial improvement” trigger that would otherwise force full flood-code compliance.
How the Fire Code Fits
The state fire code is separate from the building code but runs alongside it. Under RSA 153:1, it adopts NFPA 101 (Life Safety Code, 2021 edition) and NFPA 1 (Uniform Fire Code, 2021 edition), along with any national standard those two codes reference unless amended by the state board of fire control.9NH Division of Fire Safety. Fire Codes Adopted for NH Unlike the building code’s enforcement split, the fire code applies statewide as a minimum standard in every municipality.10New Hampshire Division of Fire Safety. State Fire Code
Sprinklers are required in many commercial and multi-family residential buildings. Nursing homes, schools, and other high-risk occupancies need additional fire-rated doors, smoke barriers, and emergency lighting. Fire alarms must comply with NFPA 72 (2019 edition).9NH Division of Fire Safety. Fire Codes Adopted for NH The State Fire Marshal’s Office oversees fire regulations for public buildings and multi-unit dwellings; local fire departments handle routine inspections where a town has adopted enforcement.
Penalties for Violations
Building code violations can trigger civil penalties, criminal charges, or both. Under RSA 676:17, the civil penalty is $275 per day for a first offense and $550 per day for each subsequent offense. Each day the violation continues after conviction or after written notice counts as a separate offense. A natural person who violates the code commits a misdemeanor; a corporation or other entity commits a felony.11New Hampshire General Court. New Hampshire Code 676:17 – Fines and Penalties, Second Offense
Local enforcement can also issue citations through a streamlined process under RSA 676:17-b, with a single citation covering up to five days of violation. Hazardous conditions can produce a stop-work order that halts all construction until the problem is corrected. In towns that require a certificate of occupancy, a building occupied without one can be ordered vacated. Code violations that contribute to injuries or property damage can create civil liability as well.
Variances and Appeals
When strict compliance would cause practical difficulty or is unnecessary to meet the code’s safety goals, you can request a variance or an alternative compliance method. Building code variances are handled locally by the building official or a local building code board of appeals, not by the state fire marshal’s office. The fire marshal handles fire code variances for state-owned buildings and directs building code questions to local officials.12New Hampshire Division of Fire Safety. Fire Code Variances
If you disagree with a local building official’s decision, the first appeal goes to the local building code board of appeals. From there, further appeals go to the State Building Code Review Board, which hears disputes over the application and enforcement of the state building code, decisions by local building officials, decisions by local appeals boards, and decisions by the fire marshal on either the building or fire code. The Board also hears appeals from the Electricians’ Board, the Board of Home Inspectors, and the Mechanical Licensing Board.13New Hampshire Division of Fire Safety. State Building Code Review Board
The Board must hold a hearing within 40 days of receiving an appeal and issue a decision within 30 days after the hearing closes.14New Hampshire General Court. New Hampshire Revised Statutes Section 155-A:11-a Starting July 1, 2026, enforcement agencies must provide information about both local and state appeals processes whenever they issue a building permit or notice of violation, and no fee can be charged to appeal a notice of violation or other decision by a code official.15New Hampshire General Court. New Hampshire Revised Statutes Section 155-A:7 – Enforcement Authority An unfavorable Board decision can be taken to Superior Court under the state’s general administrative review procedures.