New opportunities for wood construction in the 2020 NBC: Highlights from the Canadian Wood Council Code and Standards Team
By The Canadian Wood Council
By The Canadian Wood Council
The 2020 National Model codes were recently published on March 28, 2022 by the National Research Council of Canada (NRC). The Canadian Wood Council supports the updates to the 2020 NBC code.
Robert Jonkman, Vice President, Codes and Engineering comments that “The updated National Building Code expands opportunities for wood construction significantly including new provisions for mass timber of up to 12 storeys, making sustainable, low-carbon buildings easier to achieve”.
Significant Technical Changes to the 2020 National Model Codes include:
Part 2: Farm Buildings
- A new Part has been added to the NBC for (large) Farm Buildings, a much-needed update to the 1995 Farm Building Code.
- Standard farm buildings are permitted to be combustible (wood) construction of unlimited size
- Wood frame construction benefits from its inherent resistance to earthquakes, qualifying to be exempt from seismic design provisions in low seismic areas of Canada (which coincides with the majority of farmland in Canada, excepting the BC Interior and St. Laurence Valley in Ontario and Quebec).
Part 3: Fire Protection
- Encapsulated mass timber construction (EMTC) is introduced enabling the construction of wood buildings up to 12 storeys. Mass timber elements are encapsulated in order to delay the involvement of mass timber elements in a fire. Compensatory measures are also implemented.
- The methodology for determining the fire resistance of large cross-section wood elements within CSA O86, “Engineering design in wood” is introduced to Appendix D of the NBC as a prescriptive fire resistance rating calculation method for mass timber members constructed of glued-laminated timber, solid sawn timber, structural composite lumber, or cross laminated timber.
- A descriptive list of prescriptive exterior wall assemblies using wood products that are deemed to satisfy the fire protection requirements for exterior cladding/wall assemblies have been introduced into Appendix D of the NBC. These generic exterior wall assemblies may consist of wood studs, CLT and/or fire retardant treated plywood and can be used for any noncombustible, wood framed midrise or tall wood mass timber building.
- To increase design options for mid-rise buildings of combustible construction, the unique requirement that 25% of the perimeter of a mid-rise building be located within 15 m of a street may be reduced to 10% when the exterior wall cladding is noncombustible or passes a specific fire test. This change will allow for greater design flexibility in regard to property use and planning for developments that may only face a single street.
Part 4: Structural Design
- Two new types of seismic force resisting systems (SFRS), with moderately and limited ductility cross-laminated timber shear walls (platform-type construction) have been introduced. Both systems are permitted to be used for 30 m and 20 m building heights, depending on the seismic-severity of the building location.
- Guidance from the Structural Commentaries on serviceability loading criteria is revised and moved into the NBC to ensure that appropriate load combinations are used for serviceability limit state design.
Part 9: Housing and Small Buildings
- An energy efficiency performance compliance path is established with 5 tiers, each successive tier being increasingly stringent in terms of energy consumption and heat loss. A prescriptive compliance path based on energy conversation points is provided for tier 2 (tiers 3-5 will be developed for the next code cycle). Wood frame construction and mass timber construction are adaptable and can easily comply with any energy efficiency tier.
National Fire Code of Canada (NFC)
- Measures to address fire safety during the construction process of encapsulated mass timber buildings (EMTC) are included.