Hi , I'm planning on putting some decking down to cover a concrete "patio". Decking will be supported on one side on house wall on the another side on retaining wall. There is also few problems: 1) one of the decking frame (left side of the drawing) will be a base for the shed. 2) manhole And the question is what size of joist i should use? I was thinking about 100x47 (supported by two beams underneath) but am afraid of bouncing, so maybe 125x47 will be the better option, or maybe 150x47 unsupported will do the job? Thanks in advance.
100x47 supported at around 1m intervals will be fine. That isn't going to bounce much if at all. You could add noggins at the mid point to beef it up a bit.
I can't do this other way mostly because of a manhole, also I think that it will be easier this way to put it together. And as part of the deck will bi covered by shed (floor made from plywood) the boards will have less than 5m.
Thank you for reply. I'm planning to buy longer joist so the leftovers I can use as noggins but i just don't include them in the drawing. Do you think that I can use 100x47 under the shed asswell or I shoud go for 150x47 ?
Is the patio level enough for you to have the support joists?? If not I would just drop legs down from each joist on to the patio, yes it would be a lot of them but easy enough to do.
The decking will be just under 300 mm high (level of the steps). I'm planning to support main joists by two beams and that will be laying on concrete (or some additional blocks - concrete slightly uneven). I can be wrong but this way access point to manhole is better supported.
Yes, I have in the same space shed at the moment. It's not lean to shed - there's space between shed and house about 40cm.
If its a shed construction where the floor is laid first and walls on the floor, it should be fine - the load is somewhat spread. I'm building a sub-frame for a log cabin using 95x47 but as the load is around the perimeter, I'm doubling up the perimeter timbers.