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Lateral support of timber floor joists

NZS 3604:2011 Timber-framed buildings requires timber floor joists to be laterally supported to prevent overturning. 

Lateral support can be provided by: 

  • a continuous boundary joist no less than 25 mm thick that is the same depth as the joists
  • full-depth solid blocking not less than 35 mm thick that fits tightly between joists
  • herringbone strutting consisting of two pieces of 35 x 35 mm timber set diagonally in opposite directions between the top and bottom edges of the joists.

Locations where lateral support is required:

  • at the ends of joists – boundary joist or blocking/strutting at 1.8 m centres. Where the subfloor support is provided by a foundation wall that is acting as a subfloor brace, blocking must be continuous for a minimum of 1.8 m
  • for ground floor joists along all lines of horizontal support (bearers or beams) –blocking/strutting at 1.8 m centres
  • at mid-span of joists – continuous blocking/strutting. Where floor joists span more than 2.5 m and the joist depth is 190 mm or greater (NZS 3604:2011 clause, continuous blocking is required
  • for mid-floor joists along the bracing line of all walls in the floor below that contain a wall bracing element. 

From BRANZ Guideline, May 2015