Bearer & Joist Selection
Issues to consider when selecting bearers and joists from Tables 1 and 2 are:

• Bearer and joist sizes are based on a maximum deck mass of 20 kg/m2. For higher loads refer to the Application Guide for Non-domestic Decks, Board Walks and Light Traffic Structures (as referenced at the end of this document).
  
• Bearer and joists sizes assume a minimum end bearing of 50mm, and intermediate bearing of 100mm.
  
• Availability of timber species and sizes varies from one region to the next - check with suppliers for detailed information regarding availability and refer to AS1684 (see note 3) parts 2 and 3 for other grades and sizes.
  
• 45 or 50mm wide joists are recommended in order to avoid splitting when receiving nails. Joists of 35 or 38mm width are only suitable where proprietary deck fixings are used on the side of joists.
  
• Joists may overhang bearers a maximum of 25% of the allowable single span of the selected joist. Further details, such as back-span requirements are available in AS1684 (see note 3).
  
• Double bearers should be spaced apart as shown in Figure 2. Blocks should be placed at the mid-span for spans under 2.0m, at one-third points for spans 2.0 to 3.6m, at one-quarter points for spans over 3.6m. Details on block fixing requirements are provided in AS1684 (see note 3).
  
• Unseasoned material is well suited to these external applications. In many cases a wider range of both length and section size is available.
  
  
  
  Notes
  3. AS1684 Residential Timber Framed Construction, Standards Australia, Homebush.
   

Figure 2:Notched posts with double bearers and spacer block construction