I'm building a deck in the garden, have planned, purchased and started building the deck. I've been laying out some joists on the support beams (wider timbers bolted onto the posts) that I've temporarily put in position, and I'm slightly worried that the joists I have purchased are not going to be strong enough. They feel firm enough when laid out as a test, I just don't want problems a couple of months / years down the line.
On the not so worrying side:
The timbers were listed at the merchant as joists. They don't flex significantly when I stand on a single joist and jump up and down a bit, and when I've laid a couple of decks across as pictured and stand on the deck, it doesn't feel springy.
I have enough timbers to lay the joists with 220mm centres, which seems pretty close.
The deck board I have is quite good quality - 32mm thickness.
What's worrying me:
The only thing that is really worrying me is that they 'look' a bit on the thin side, and everything I've looked up online seems to reference minimum 6 inch joist depths.
Max spacing across main support beams: 900mm
Joist spacing center to centre: 220mm
Joist with: 50mm
Joist depth: 75mm
I have read that "In general terms, joists spaced 16 inches on centre can span 1.5 times in feet their depth in inches". If this is true, they should be able to span about 1300mm, I'm only attempting 900mm. I hope that's right!
Any advice appreciated.