Proposed Change 2216

The requirements in Sentence 9.23.13.5.(3) of the 2025 edition of the National Building Code of Canada (NBC) regarding the transfer of lateral loads from roof framing members to braced wall panels are unclear and have created confusion within the truss industry. The intent of the existing Sentence is to ensure that stronger wall types (WSP‑B or higher) can effectively transfer lateral loads to and from the roof structure. However, the requirements and figures in the associated explanatory Note do not clearly illustrate how blocking elements should be constructed or connected, nor do they provide sufficient information on the design loads that blocking elements must resist or clarify the differences between partial‑ and full‑height blocking configurations.

Improper or inconsistent blocking can result in inadequate lateral load transfer, truss rotation, or damage to truss connections, potentially reducing the building’s ability to resist wind and seismic forces. The lack of clarity can also create uncertainty among designers, builders and truss manufacturers regarding how to design and apply blocking details. Inconsistent interpretation resulting from these gaps may lead to construction quality issues and non‑compliance with the intent of the requirements, posing safety concerns.

Clarifying this requirement is necessary to ensure consistent, safe and constructible methods for transferring lateral loads from roof structures to braced wall panels, while maintaining the prescriptive nature of Part 9.

This proposed change clarifies the current requirements for transferring lateral loads from roof structures to braced wall panels and expands on them by directly addressing the missing technical detail and risk of inconsistent interpretation identified in the current provisions. The new Article 9.23.13.6. and its accompanying tables establish prescriptive requirements for solid blocking, blocking panels and engineered truss panels, including their construction, materials and fastening details. These proposed revisions are intended to resolve confusion about how blocking elements should be constructed and connected, thereby reducing the likelihood of improper load transfer and limiting the probability of damage to roof components.

This proposed change introduces consistent fastening patterns and acceptable materials (such as solid lumber or structural composite lumber), and references venting provisions for full‑height blocking to maintain attic ventilation. By referencing the factored shear resistance values in new Table 9.23.13.6.‑C, this proposed change specifies that blocking or truss panels must meet or exceed the strength of the braced wall panel below, which addresses the uncertainty about load capacity and would improve reliability in lateral load transfer. Clear differentiation between full‑height and partial‑height configurations—including specific fastening requirements and minimum gaps for partial‑height blocking—would reduce confusion in application and limit the probability of inadequate load paths or truss movement. Collectively, these clarifications provide a consistent prescriptive method that supports safe, practical and verifiable roof‑to‑wall load transfer practices.

Implementing this proposed change at the National Model Code level is the most effective approach to resolve the problem that originated in the wording of the NBC 2025 and affects prescriptive construction practices. This proposed change promotes the consistent interpretation of the requirements for transferring lateral loads from roof structures to braced wall panels and their application where the National Model Codes are adopted by provincial and territorial authorities. This proposed change also limits the probability of unsafe conditions under wind and seismic loading, and maintains the prescriptive intent of NBC Part 9 while improving clarity, consistency and constructability.

The proposed change is expected to result in cost savings. Although there are costs associated with the installation of solid blocking, blocking panels, or truss panels (see table below), the requirements, as clarified by this proposed change, provide the necessary guidance to reduce the need to pay professional fees (see the “Benefit Analysis” section below).

Cost Analysis

This proposed change does not introduce new requirements for blocking to facilitate lateral load transfer; since the requirements already exist, there is an existing cost associated with the existing requirement. However, this proposed change clarifies the requirements for blocking, which may result in cost savings.

The costs for blocking are determined based on the construction and connection details that are chosen as a result of the reasonable interpretation of the existing requirements in Sentences 9.23.13.5.(3) and (4)-2025 as shown in the figures included in the explanatory Note. The cost analysis of this proposed change includes a range of costs reflecting possible interpretations of the existing requirements (and figures, i.e., the visual interpretation of the engineered solutions that are provided by a professional engineer).

The cost analysis also includes the assumptions identified below.

Table 1 shows an assessment of the difference in costs of the existing requirements for blocking compared to the requirements as clarified in this proposed change (i.e., Article 9.23.13.6.-2030).

The two locations have been selected to represent both an area with low-to-moderate wind or seismic forces (i.e., Toronto, Ont.) and an area with high wind or seismic forces (i.e., Victoria, BC), using climatic data and seismic parameters from NBC Tables C-2 and C-3.

The A4 building archetype features brick veneer on the front elevation and stucco siding on the sides. In Toronto, these claddings classify the construction as heavyweight. In Victoria, however, heavyweight construction would require longer exterior walls than available; therefore, vinyl siding is used instead to classify the construction as normal weight.

Table 1. Construction Costs^(1)(2)(3) for Lateral Load Transfer Blocking in Two Locations

Notes to Table 1:

1.    Costs are based on RSMeans data from Gordian for 2026 Q1.

2.    Cost adjustments per RSMeans include a 15% mark-up for difficulty working within trusses, a 20% contingency allowance since the estimate is based on conceptual design, and a 10% construction management fee, plus overhead and profit.

3.     The assessment of existing costs is based on Sentences 9.23.13.5.(3) and (4)-2025 (as shown in the figures in the Note as specified). For the lower cost value in the third column of Table 1, the analysis assumes 38 × 89 mm blocking and 11 mm OSB sheathing at the truss heel (see Figures A-9.23.13.5.(3) and (4)-2025, Raised heel truss) with heel heights of 286 mm and 600 mm for solid blocking and blocking panels, respectively. For the higher cost value, the analysis assumes an engineered solution similar to that required by Article 9.23.13.6.-2030. The range of existing costs associated with Sentences 9.23.13.5.(3) and (4)-2025 reflects a reasonable interpretation of the figures in the explanatory Note.

4.    Costs for solid blocking in accordance with Article 9.23.13.6.-2030 are based on a raised heel truss between 140 mm and 286 mm and 38 × 286 mm solid blocking.

5.    The quantities of solid blocking and blocking panels were determined by calculating the length of required braced wall panels for the A4 building archetype (see supporting documents) using the Calculation Method in NBC Article 9.23.13.9. and are specific to the climatic data and seismic parameters for the two locations.

6.     Costs for blocking panels in accordance with Article 9.23.13.6.-2030 are based on a raised heel truss of 600 mm and use 38 × 89 mm top, bottom and side framing with 11 mm OSB sheathing to match the WSP-B blocking panel below.

7.     The cost difference for engineered truss panels is based on data provided by the Western Wood Truss Association of British Columbia and reflects expected design efficiencies resulting from the proposed clarification of the loads in Sentence 9.23.13.6.(9)-2030. The resulting design efficiencies are expected to reduce costs by approximately $2.75 per 600 mm tall panel between trusses and $3.10 per 1 200 mm tall panel between trusses. Based on the A4 building archetype, fifteen 600 mm panels are required in Toronto, representing an estimated cost savings of approximately $41. In Victoria, twenty‑two 600 mm panels and one 1 200 mm panel are required, representing an estimated cost savings of approximately $64.

Benefit Analysis

As identified in the Problem section, Subclause 9.23.13.5.(3)(b)(i)-2025 lacks clarity regarding construction requirements for blocking panels, leaving the interpretation to the builder or owner. Alternatively, the roof truss manufacturer can support compliance by designing to meet the lateral load transfer requirements. In both cases, a professional engineer is likely needed to develop the solution and/or to specify the design loads, resulting in additional engineering fees. Representatives of the Western Wood Truss Association of British Columbia report that these fees are typically $1 500 to $2 500 in Victoria, depending on building size. The lateral load provisions in NBC 2025 have not yet been adopted in Ontario; therefore, the requirement does not currently exist in Toronto and the corresponding engineering fees remain unknown. As such, professional fees in Toronto are assumed to be the same as in Victoria for the purpose of this analysis.

This proposed change benefits Code users by clarifying the requirements, which in turn means engineering fees can be saved, resulting in a cost savings of $1 500 to $2 500. For the purpose of this analysis, based on the area of the A4 building archetype (1 373 ft.²), the lower end cost savings ($1 500) is used for comparison against the costs provided in Table 1 above.

Conclusion

This proposed change offsets the new costs for blocking with the costs saved related to professional fees. Therefore, the cost impact for the proposed change is a net savings ranging from $920 ($1 500–$580) to $1 459 ($1 500–$41), depending on the blocking type and location. The net cost reduction represents the overall benefit of making the proposed changes.

The proposed change provides regulators with additional prescriptive information to support the assessment of compliance, improving enforceability compared to the current NBC requirements. Multiple options are provided to allow flexibility during construction and to support enforcement across the range of scenarios that may be encountered on site.

Some training may be required, particularly in regions where lateral load bracing requirements are relatively new (e.g., areas with low-to-moderate seismic and wind loads). However, the figures included in the explanatory Note are expected to support training and improve general understanding of the requirements.

This proposed change addresses concerns raised by the truss industry and supports manufacturers by providing information for the design and construction of engineered truss panels where roof trusses are used as roof framing. This proposed change removes the need for roof truss manufacturers to retain professional engineers to determine the loads that engineered truss panels must be designed to meet or exceed, thereby reducing the associated time and costs.

This proposed change also provides information to support builders when site-built lateral load transfer blocking is used instead of engineered truss panels, or where the roof framing does not consist of roof trusses (e.g., where rafters or joists are used instead).