Karl, the second diagram shows the joists running across the span, this is the way the decking boards are going to run, so if I just flip it around 90 degrees, then that will still work, won’t it. Tried some online tools to work out the diagram, got absolutely nowhere and you produce it for me that quickly. Amazing.
Assuming a 1.5kN load is required, C16 joists and rebated 100mm posts the following applies for a decking structure 5.5m x 3.5m
The beams are set out 1.375m spans (between posts) with the beams at 1.7m spans.
The joists are then sat on top of the beams at 400 centres.
The method of orientation will cost more, more posts, more labour. The reason for the dimensions, well this does apply the above principal of joist, and beam spans and as you need the additional components one may as well space them equidistant.
Is it your wife who is the boss at the supply place where I got my oil and products from? Would like to get you a bottle of something for your help so could use her business address to send it to. What’s yr poison, single malt or something?