Looking for a little advice on building frame for composite decking. Previous built decking on concrete base but this one will be raised due to ground not being level. The decking i want to build is 8.4m wide x 3.6m. The decking comes in 3.6m lengths so this is why i plan on having the decking this size to save on wastage. I was thinking about 7 posts along front and back at 1.2m a part. Along the sides putting one in the middle. Is this enough? The joists have to be 300mm apart and I planned to use 2 x 6 for the joists. Can anybody tell me how many posts I will need to place to support the joists? Without counting the outer frame there will be 11 rows of joists. Would you recommend using joist supports or just use old fashion nails? Thanks
That is one big deck. So the joists will be running down the 8.4 length then I assume? I think the post spacing you mention would work but I think you would want a supporting joist running from post to post across the 3.6 span? I am just about to build a deck of pretty much the same size, but have opted to run the joists across the width because it will require less timber (I think - it certainly seems simpler). I would say you only need joist hangers if one or more sides will be attached to the house. If it's free standing and you have enough access from all sides then just secure them with coach screws.
You say 7 posts at 1.2m, you need 8 at 1.2m to give 8.4m See following re my decking, I would be inclined to use 5 posts at 2.1m along the front and back and 2 post within the central section of the 3.4m cross pieces i.e. at 1.15m . In theory I think it saves you 1 post https://community.screwfix.com/threads/decking-frame-questions.222480/#post-1790156
My thoughts to but OP said joists have to be 300 apart so I assumed that is what the composite decking suppliers have speced?
Apologies, it should have read 1.4 apart. Also thinking of putting 2 at the sides at 1.2 apart, counting the two front and back that makes 4 on the 3.6m length. Then putting the same with a joist running front to back at 2.8 & 5.6. Do you think this too much?
Then I'd go for my original suggestion of 5 posts at 2.1m ( could be 2.4m with 1.2m make up piece at the end or middle) in the 8.4m direction and 4 posts in the 3.6m direction. This gives 20 posts, your idea gives same number but suggestion means all 3.4m cross members have more support as theses are the members with most load acting on them. Actual allowable span taken from building regs floor joists tables gives an allowable span of the 150 x 50 supporting your decking boards spaced a 400 centres as 3.5m, so even if youhave 4 posts at 2.8m in the 8.4m direction it would be acceptable. Choices,choices,choices!!! How high off the ground is your decking
The decking will be about 300mm off the ground. Do you have any recommendations for screws to attach the joists to the posts? I was thinking of using Coach screws
Used 1/2" coach bolts on mine but posts were free standing and deck 600 off ground so did not want any sway. If you are setting posts in ground every thing will be rigid and coach screws should suffice Used 6" nails to connect joists to each other
Thanks for the advice. Just need the company to come back with a quote for me now for all the stuff. have you ever done a picture frame round the decking before? Just saw some pictures of it and thought I might do that.
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