New Hampshire Energy Code Requirements and Compliance

New Hampshire energy code requirements come from the 2018 International Energy Conservation Code, as amended by the State Building Code Review Board and adopted statewide under RSA 155-A. Every new building and every significant renovation in the state must meet it, and the contractor, not the town, carries legal responsibility for compliance.¹ The 2018 edition took effect on July 1, 2022 through House Bill 1681, and as of mid-2025 the state has not moved to the 2021 or 2024 IECC.²

The version of the code in effect on the date your building permit application is received governs your project through completion.¹ So the specs below are what you build to today.

Which Climate Zone You Are In

New Hampshire straddles two IECC climate zones, and the zone sets your insulation values, slab details, and wall assembly options. Get the zone wrong and the compliance package comes back rejected before you break ground.

Zone 5 covers Cheshire, Hillsborough, Rockingham, and Strafford counties.
Zone 6 covers every other county, plus the town of Durham, which sits in Strafford County but is classified as Zone 6.³

Both zones share the same ceiling and window thresholds. The walls are where they split, and the split is big enough that a Zone 5 assembly will fail inspection in Zone 6.

What Projects Have to Comply

The code reaches further than new construction. Any significant addition, alteration, or renovation to an existing building triggers the energy code for the scope of that work, and a change of occupancy type can trigger it as well. Converting a house to a commercial office, for example, means the renovated space must meet the commercial standards.

Residential provisions apply to one- and two-family homes and townhouses no taller than three stories above grade. Everything else, including multi-family apartments, offices, retail, and industrial facilities, falls under the commercial provisions.

A short list of buildings is exempt from the full thermal envelope and mechanical rules:

Low-energy buildings with a peak energy use of less than 1 watt per square foot, such as unheated storage or certain agricultural structures.
Mobile homes, which are regulated under federal HUD standards instead of the IECC.
Historic properties that are listed on the State or National Register of Historic Places, designated under local or state historic preservation law, or certified as contributing resources within a listed historic district.⁴

The historic exemption rides on registration or eligibility for registration, not age. A 200-year-old farmhouse that is not listed and not eligible for listing has to comply when renovated.

Insulation, Windows, and Air Sealing

The thermal envelope is where most residential compliance work lives.

Insulation Values

Flat ceilings in both zones require R-49 insulation. An R-38 assembly works if it maintains the full R-value over the top plates. Sloped or cathedral ceilings can drop to R-30 when the area is less than 500 square feet or 20 percent of the total ceiling area. Basement and crawl space walls require R-19 cavity insulation or R-15 continuous insulation in both zones.³

Above-grade walls diverge by zone:

Zone 5: R-20 cavity insulation alone, or R-13 cavity plus R-5 continuous insulation, meeting a maximum assembly U-factor of 0.060.
Zone 6: R-20 cavity plus R-5 continuous insulation, or R-13 cavity plus R-10 continuous insulation, meeting a maximum assembly U-factor of 0.045.³

You cannot use cavity-only R-20 in Zone 6. Continuous exterior insulation is required, and the added thickness has to be worked into window and door rough openings from the start of framing.

Windows and Doors

Windows and glass doors cap at a U-factor of 0.30 in both zones. A narrow exception allows U-0.32 for log-wall construction in Zone 5 only.³ Skylights have a separate, more lenient threshold. Look for the National Fenestration Rating Council label on each unit; the tested U-factor on that label is what the inspector compares against the code.

Air Leakage

Every penetration in the envelope, including electrical outlets, plumbing, and recessed lighting, must be sealed. The finished home then takes a blower door test. In both zones the maximum allowable air leakage is 3 air changes per hour at 50 Pascals (3 ACH50).⁵ Failing this test is a common reason a project stalls at final inspection, and chasing leaks after drywall is up is expensive. Most experienced builders run an informal test at rough-in before closing walls.

Mechanical Systems and Lighting

Heating and cooling equipment has to be sized to the calculated load, not padded. Under the 2018 IECC, output capacity cannot exceed the smallest available equipment size that covers the calculated heating and cooling loads.⁶ Oversized equipment short-cycles, wastes energy, and creates comfort problems, which is why the code treats correct sizing as mandatory.

Ductwork in unconditioned spaces must be sealed at all joints and insulated. Ducts located outside the building envelope in climate zones 5 through 8, which covers all of New Hampshire, require a minimum of R-12 insulation.⁶ Leaky or uninsulated ducts in an attic or crawl space can waste 20 to 30 percent of the energy used to condition air.

Commercial projects also have to install automatic lighting controls. Occupancy sensors and scheduled shutoffs are mandatory for interior lighting and often for exterior lighting as well. Residential buildings are not subject to the same mandatory lighting controls.

The Compliance Package

Before a building permit issues, you assemble documentation showing the design meets the code. For residential projects the primary document is the EC-1 form, the Residential Energy Code Application for Certification of Compliance, which walks through every element of the envelope, mechanical systems, and air sealing plan.²

Most builders use the Department of Energy’s REScheck software for residential work and COMcheck for commercial. These generate a report comparing your wall, ceiling, floor, and window specifications against the prescriptive requirements for the applicable climate zone and flag anything that falls short.

Residential projects also need Manual J, S, and D calculations. Manual J sets the heating and cooling loads using the building’s size, orientation, insulation, and local climate data. Manual S matches that load to appropriately sized equipment. Manual D designs the duct system. The package should also include a plan for the blower door test, specifying when and how it will run.

Submission, Inspections, and What Failure Costs

Where you file depends on your town. If the municipality has its own building inspector or code enforcement official, the EC-1 and supporting documents go to that local office. If it does not, the EC-1 goes to the New Hampshire Department of Energy, which handles energy code review directly for roughly 100 mostly smaller and rural municipalities.²

Inspections usually happen in two stages. The rough-in inspection occurs after insulation and mechanical systems are installed but before drywall. The inspector verifies R-values, air barrier continuity, and sealing. The final inspection comes after construction is complete and generally requires blower door test results showing the building hit 3 ACH50.

Missing the energy standards can result in the certificate of occupancy being withheld, which legally prevents anyone from using the building. Where no local enforcement agency exists, the state fire marshal has authority to enforce the code, including issuing permits and conducting inspections, on written request of the municipality.⁷ A notice of violation has to identify the specific section being violated, and you can appeal a notice of violation or any code official decision at no charge.

The technical standard is the same whether you build in Manchester or a small North Country town. Municipalities cannot enact ordinances that amend, override, or deviate from the technical requirements of the state code.⁸ What varies by town is who reviews your paperwork and runs inspections.

Third-Party Plan Review

Under SB 188, effective July 15, 2025, New Hampshire allows licensed third-party professionals to conduct building inspections and construction document reviews in place of local building officials. These approved agencies must be properly credentialed as licensed engineers, architects, or ICC-certified building officials, independent of the project, and vetted by the municipality. They must carry liability insurance with minimum coverage of $2 million per occurrence and $4 million aggregate for projects costing $5 million or less, with higher limits for larger projects.¹

The practical benefit is speed when a town has a backlog or limited staff. Municipalities must also reduce permit fees by up to 80 percent when a third-party provider handles both plan review and inspections.

1
New Hampshire General Court. New Hampshire Revised Statutes Section 155-A:2 – State Building Code
2
NH Department of Energy. Energy Codes
3
NH.gov. New Hampshire Residential Energy Code Application
4
Building Energy Codes Program. What Is Required for Historic Buildings
5
Resilient Energy Codes Working Group. IECC Compliance Guide for Homes in New Hampshire
6
ICC Digital Codes. 2018 IECC Chapter 4 CE Commercial Energy Efficiency
7
New Hampshire General Court. New Hampshire Revised Statutes Section 155-A:7 – Enforcement
8
New Hampshire General Court. New Hampshire Revised Statutes Section 155-A:3 – Local Enforcement