New Hampshire adopts the 2024 I-Codes effective 1 July 2026, with mandatory compliance from 1 January 2027

New Hampshire's state building code moved to the 2024 International Codes on 1 July 2026, following enactment of HB1159-2026, signed by the governor on 8 May 2026. The update, ratified by the General Court under RSA Chapter 155-A, binds all construction statewide - residential and non-residential - and applies regardless of whether a municipality has its own building official. A six-month concurrence period runs from 1 July through 31 December 2026, during which permit applications may be submitted under either the 2021 or 2024 code editions. Beginning 1 January 2027, all permit requests must follow the 2024 codes.

What was adopted

The New Hampshire Building Code Review Board adopted the following model codes, each with state-specific amendments ratified through 10 October 2025:

• International Building Code 2024 (IBC) with New Hampshire amendments
• International Residential Code 2024 (IRC) with New Hampshire amendments
• International Existing Building Code 2024 (IEBC) with New Hampshire amendments
• International Mechanical Code 2024 (IMC) with New Hampshire amendments
• International Plumbing Code 2024 (IPC) with New Hampshire amendments
• International Swimming Pool and Spa Code 2024 (ISPSC) with New Hampshire amendments
• National Electrical Code 2023 (NEC)

The 2018 International Energy Conservation Code (IECC) remains in effect; New Hampshire did not advance to the 2021 or 2024 IECC editions in this cycle.

The substantive change: snow load methodology

The most consequential structural change carried in by the 2024 IBC is the shift to ASCE 7-22, "Minimum Design Loads and Associated Criteria for Buildings and Other Structures," as the referenced standard for snow loads under IBC Chapter 16. The 2024 IBC replaces the ASCE 7-16 ground snow load maps with new risk-category-specific maps based on ASCE 7-22, which incorporate 25 to 30 years of additional snow load data and a shift from service-level to strength-based (reliability-targeted) ground snow load values.

Practically, this changes how load combinations are structured. Under ASCE 7-22, the LRFD load factor for snow drops from 1.6S to 1.0S, and the ASD factor drops from 1.0S to 0.7S, because ground snow load values are now expressed at strength level rather than service level. The snow importance factor has been eliminated; separate ground snow load maps are now provided for each risk category. Structural engineers and truss designers working on projects permitted after 1 January 2027 must use the ASCE 7-22 methodology and maps, not the ASCE 7-16 values carried in the 2021 IBC.

The 2024 IRC retains ASD-based ground snow load figures for prescriptive sizing tables, but those figures differ from the IBC/ASCE 7-22 strength-level values. Designers using engineering software should confirm which load type - service-level or strength-level - their tools expect before inputting ground snow load values.

Local amendment authority narrowed

As of 1 July 2026, municipalities that choose to enforce the state building code may adopt local amendments only on administrative matters; substantive local modifications to technical requirements are no longer permitted under RSA 155-A. Local ordinances must be confirmed by the Building Code Review Board and may not be less stringent than the state code.

Permit transition and who it affects

During the concurrence period through 31 December 2026, applicants may elect either the 2021 or 2024 code edition at the time of permit submission. Projects already permitted under the 2021 codes are not required to resubmit. After 1 January 2027, no new permit applications may be reviewed under the 2021 edition.

The adoption affects structural engineers, residential builders, commercial contractors, and mechanical, plumbing, and electrical trades statewide. The authority having jurisdiction determines compliance questions where the adopted text is ambiguous. Nothing in this article constitutes legal or compliance advice; readers should consult the adopted instrument and the Building Code Review Board for authoritative guidance.

The Building Code Review Board continues to accept amendment proposals on an ongoing basis; any amendments approved after the 10 October 2025 ratification cutoff will apply to a future code cycle, not the current 2024 edition.