Making the base for my decking which is basically two 5.4 m joists running length wise with 14 joists across the way. What is the spacing for the cross joists , ie at what interval along the length do I put the cross joists in? So the length is 5.4m the joists are 50mm thick and I have 14 of them. I appreciate that this is potentially very easy to work out and apologise in advance for my extreme thickness.

standard is at approx 400mm but should be fine at 500 as long as you use a thick deck board rather than cheap thin ones

just done the math very quickly and your joists assuming 50mm thick will be 411.5mm center to center (remember first center is 25mm in from each end)

411.5mm

[edit] See above for equally correct but speedier answer

Cheers hustler/muppet. How do you work it out?

How do you work it out?

Take your overall length: 5400mm

Subtract the thickness of one joist: 5400mm – 50mm = 5350mm

Divide by the number of joists-1 (or number of gaps): 5350mm / 13 = 411.538mm

Round it up/down: 411.5mm

I’d be asking what size are your 5.4’s if supported only at each end 😉