2025 National Model Codes: What Changed for Housing, Energy, Retrofits, and Plumbing

The Canadian Board for Harmonized Construction Codes (CBHCC) approved a substantial set of technical changes in the 2025 editions of Canada's National Model Codes, including an update to the referenced documents in Table 1.3.1.2. across all of the National Model Codes. This article focuses on a selection of changes relevant to the National Building Code, the National Plumbing Code, and the National Energy Code.

National Building Code - Part 9: Housing and Small Buildings

Radon and soil gas mitigation: The code now requires a passive vertical radon stack in dwelling units and home-type care occupancies wherever a floor assembly separates a conditioned space from the ground. Alongside that, the overlapping seams of air barriers under concrete slabs must now be sealed, and the code clarifies the type and thickness of ballast to be applied over exposed air barriers in heated crawl spaces.

National Building Code - Section 9.36: Energy Efficiency

Fenestration and door thermal characteristics: The code places an upper limit on the solar heat gain coefficient for fenestration and doors, with the limit depending on the fenestration-and-door-area-to-gross-wall-area ratio (FDWR) and the building's climate zone.

A new energy use intensity path: An optional energy use intensity path is introduced, 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. Notably, it recognizes the inherent energy savings of smaller and more compact housing forms.

Points-based prescriptive trade-off path: The optional energy conservation measures (and the points attached to them) are revised, with updates covering 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. The code also sets the minimum sums of energy conservation points required to comply with Energy Performance Tiers 3, 4 and 5.

Simple prescriptive compliance for Tiers 1 and 5: The code adds an optional simple set of prescriptive energy efficiency requirements for demonstrating compliance with Energy Performance Tiers 1 and 5.

Operational greenhouse gas emissions: Section 9.36 introduces both performance and prescriptive requirements (within a framework of gradually increasing reduction levels) to establish limits on the operational greenhouse gas emissions.

National Building Code - Part 10: Alteration of Existing Buildings (New Part)

This is one of the most significant additions in the 2025 edition - an entirely new Part dedicated to the alteration of existing buildings.

Part 10 clarifies how requirements apply when improving the energy performance of existing Part 9 buildings undergoing alteration, covering HVAC and service water heating systems, above-ground opaque and below-grade assemblies, fenestration, doors and skylights, and the airtightness of air barrier systems. It also introduces two new defined terms: "existing building" and "heritage building."

National Building Code - Appendix C: Climatic and Seismic Information

The climatic design data in Table C-2 has been updated to take into consideration projected future changes over a 50-year time horizon. In practice, this means design increasingly accounts for the conditions a building is expected to experience across its service life.

National Plumbing Code

New and revised defined terms: The code introduces "washroom," "public washroom," "private washroom," and "macerating toilet system," and revises the defined terms "public use" and "private use."

Condensate drainage: A new defined term "condensate drainage system" is added, the terms "clear-water waste" and "drainage system" are revised to address condensate drainage, and new requirements for condensate drainage systems are introduced.

Storm and sanitary drainage: Requirements for the storm drainage of roofs with certain configurations are clarified, including the use of scuppers or emergency roof drains, with additional design options provided. Storm and sanitary drainage systems must now also be labelled according to their application, so contractors and municipal plumbing inspectors can readily tell them apart.

New referenced standards: The NPC now references:

• ASME A112.6.1M-1997 for wall carriers for water closets;

• CAN/ULC-S656-14 for oil separators (oil interceptors);

• NSF/ANSI/CAN 61-2020 to address protection of potable water from chemical contamination, and CSA B214:21 to address potable water used as a hydronic fluid in an open-loop heating system;

• ANSI/AWWA C227-17 for plain-end-type mechanical (bolted, split-sleeve) couplings in pressure applications.

Neutralization tanks: Dilution is removed as an option for treating corrosive or acid waste and neutralization is retained.

National Energy Code of Canada for Buildings (NECB)

Thermal bridging: Part 3's thermal bridging requirements are updated, with a new reference to CSA Z5010:21 for thermal bridging calculation methodology. Thermal bridging due to fasteners and other point elements that penetrate the insulation layer must now be accounted for in the calculation of an assembly's thermal resistance.

Energy modeling software: Software used to demonstrate code compliance must now pass the acceptance criteria set out in ASHRAE 140-2023, "Method of Test for Evaluating Building Performance Simulation Software." The code also introduces requirements for exceptional calculation methods, to handle building components that the energy modeling software can't otherwise represent.

Energy use intensity compliance path: An optional EUI compliance path is introduced for multi-unit residential buildings, schools, and office buildings, in which the proposed building's annual energy consumption is compared with a building energy target based on the energy use intensity of the building archetype.

Operational greenhouse gas emissions: The NECB introduces performance requirements within a framework of gradually increasing reduction levels to establish limits on the operational greenhouse gas emissions.

Alteration of existing buildings: Mirroring the NBC, the NECB adds a new Part for the alteration of existing buildings, clarifying how energy-performance requirements apply to the building envelope and to HVAC, service water, lighting, and electrical power systems in existing buildings undergoing alteration. It, too, introduces the defined terms "existing building" and "heritage building."

These changes point in a consistent direction. Buildings are designed for their future climate rather than their past, energy performance is measured in more than one way through energy use intensity and operational carbon, and, a framework for improving the existing building stock is set through the new alteration provisions.

For those designing, retrofitting, or owning buildings in Canada, these changes are worth understanding well ahead of provincial adoption. Reach out to GSP Engineering to discuss how these changes may affect your projects and how we can help you prepare.

Ahmad Hammouz, P.Eng., LEED AP BD+C