Here are the changes in the 2025 NBC.

January 27, 2026

By Canadian Board for Harmonized Construction Codes

The Canadian Board for Harmonized Construction Codes (CBHCC) has released the 2025 National Building Code. The NBC is a model code that provinces use as a basis for their own codes. Different provinces will now publish their own codes or adopt the NBC in its entirety over the next year or two.

The CBHCC has published a list of important changes in the 2025 NBC. Here are some items of interest to residential builders and renovators:

Snow loading

• Part 4 specified wind and snow loads to reflect have been revised to reflect a “uniform risk” by reducing load factors for wind and snow to 1.0 and by using 1/500 annual probability wind loads and 1/1000 annual probability snow loads;
• The snow load formula has been revised by adjusting the wind exposure factor (C_w) and the accumulation factor (C_a) to account for differences in the winter average temperature (T_ws) and winter average wind speed (V_ws) across Canada, and by introducing a thermal factor (C_T) to account for a reduction in snow depth due to heat loss through the roof. This aligns Part 9 with the changes to wind and snow loading in Part 4.

Radon and soil gas mitigation

• A requirement has been introduced to provide a passive vertical radon stack in dwelling units and home-type care occupancies where a floor assembly separates a conditioned space from the ground;
• NBC 2025 requires the overlapping seams of air barriers under concrete slabs to be sealed, and clarifies the type and thickness of ballast to be applied over exposed air barriers in heated crawl spaces.

Lateral loads

• The seismic design parameter used in Part 9 has been updated from S_a(0.2) to S_max. New prescriptive framing type options have been added for braced wall panels, and the requirements for bracing to resist lateral loads in locations with low seismic and wind loads have been added.

Wall studs

• Table 9.23.10.1 “Size and Spacing of Studs” has been revised to clarify that 38-by-140 millimeter studs spaced at 400 mm can be used in exterior walls supporting a roof or a roof plus one floor.

Protection from precipitation of rough opening sills

• NBC 2025 clarifies the requirements for protection from precipitation of rough opening sills for windows and doors to improve alignment with established building science principles and standards, specifically, that rough openings allow for water drainage and be sufficiently wrapped.

Thermal characteristics of fenestration and doors

• For the first time, the building code places an upper limit on the solar heat gain coefficient for fenestration and doors that depends on the fenestration and door area to gross wall area ratio (FDWR) and the climate zone of the building location.

Energy use intensity path

• The update introduces an optional energy use intensity path in which compliance with the energy performance tiers is demonstrated by meeting an annual energy consumption target, an annual gross space heat loss target, and a design cooling load budget and that recognizes the inherent energy savings of smaller and more compact housing forms.

Points-based prescriptive trade-off path

• The optional energy conservation measures, and corresponding points, available in the prescriptive trade-off path for demonstrating compliance with the energy performance tiers has been revised. It includes updates related to drain-water heat-recovery units, oil- and gas-fired furnaces, air-source heat pumps, heat/energy recovery ventilators, the building envelope, airtightness and fenestration and doors.
• This edition sets the minimum sums of energy conservation points required for compliance with Energy Performance Tiers 3, 4 and 5.

Prescriptive compliance for Energy Performance Tiers 1 and 5

• NBC 2025 provides an optional simple set of prescriptive energy efficiency requirements for demonstrating compliance with Energy Performance Tiers 1 and 5.

Operational greenhouse gas emissions

• This code introduces both performance and prescriptive requirements, within a framework of gradually increasing reduction levels, to establish limits for operational greenhouse gas emissions resulting from the supply and consumption of energy used by the building, as determined at the time of design.

Alteration of existing buildings

• NBC 2025 introduces a new Part that applies to the alteration of existing buildings to clarify the application of requirements to improve the energy performance of HVAC and service water heating systems, above-ground opaque and below-grade assemblies, fenestration, doors and skylights and the airtightness of air barrier systems in existing Part 9 buildings subjected to alteration;
• The new Part introduces the defined terms “existing building” and “heritage building.”

Thermal bridging

• Thermal bridging requirements in Part 3 have been updated and a reference to CSA Z5010:21, “Thermal bridging calculation methodology,” added to provide guidelines for thermal simulation;
• NBC 2025 requires that thermal bridging due to fasteners and other point elements that penetrate the insulation layer be accounted for in the calculation of thermal resistance of the assembly.

Application of Part 4

• The update clarifies that Part 4 applies to lighting components and systems that are in the building, connected to the building’s electrical service, or located on the building site.

Energy modeling software

• NBC 2025 requires the energy modeling software used to demonstrate code compliance pass the acceptance criteria set out in ASHRAE 140-2023, “Method of Test for Evaluating Building Performance Simulation Software”;
• The code introduces requirements for exceptional calculation methods, and for related documentation, for building components that cannot be modeled by the energy modeling software.

Operational greenhouse gas emissions

• NBC 2025 introduces performance requirements within a framework of gradually increasing reduction levels to establish limits for operational greenhouse gas emissions resulting from the supply and consumption of energy used by the building, as determined at the time of design.

Updates to climatic data

• Updates to climatic data in Table C-1 now include projected future values of July design temperatures and hourly wind pressures that incorporate the effects of climate change.