Proposed Changes to the National Building Code: Lateral Load Bracing
National Building Code is proposing changes to lateral load bracing to resist seismic and wind forces.
Which option do you currently use? a. Build braced wall panels according to the prescriptive tables in the BC Building Code for Part 9 (that specifies anchor bolt spacing, type of sheathing, fasteners and spacing, according to your location’s seismic values.) b. Hire a structural engineer to design your braced wall panels. (You will probably not be affected by the proposed changes.)
Impact 1 – Tighter spacing of fasteners and anchor bolts: Builders using Part 9 prescriptive tables for braced wall panels in higher seismic zones (such as locations in Vancouver Island) will need to comply with tighter spacing of fasteners and anchor bolts (no screws allowed.) See example on page 3. - Seismic values for locations have been updated (Table 9.4.1.1.) o Several locations in Vancouver Island will be above the seismic value Smax of 1.4 (assuming soil type Site Class C): Duncan, Jordan River, Langford, Port Alice, Port Renfrew, Sidney, Sooke, Tofino, Ucluelet, Victoria
Impact 2 – Limited Length-to-Width Ratio: Builders who are using the Part 9 prescriptive tables for braced wall panels in locations with hourly wind pressure (HWP) greater than 0.35 kPa (i.e. most of BC is above this value) cannot exceed a 2:1 length-to-width building ratio, unless the braced wall panel length is increased. See diagram below.
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Impact 3 – Increased min. total lengths of braced wall panel: Builders who are using the Part 9 prescriptive tables for braced wall panels in higher seismic zones (such as locations in Vancouver Island) will need longer braced wall panels. See diagram below.
Impact 4 – Increased min. lengths of cripple/knee/pony walls: Builders who are using the Part 9 prescriptive tables for cripple/knee/pony wall bracing in higher seismic zones will need to add 20% more length (to a max. of 5 m length, 0.35 m height). See diagram below.
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Example of 2 Storey House in Victoria and Sooke:
Victoria: Smax 1.749 HWP 0.57 kPa
Sooke: Smax 1.836 HWP 0.48 kPa
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