Deck joist support question

[bobnotthe builder]

Found answers to my previous question a couple of days ago by looking through previous posts (doh!).....but now got another one which I can't find an answer to!

I'm doing a freestanding deck 3.6m square. there's no patio underneath so I'm going to support the framework on posts set in concrete. I'm a bit confused about how much support is needed though. I followed Thermo's advice (lots of other brilliant tips going through the posts - thanks) to look at www.richardburbridge.co.uk and the decking showed there has supports (concrete slabs) at 1.8m points round the outside of the frame but not all the inner joists are supported - they're just connected at their ends to the outside. Is that right? I'm thinking that my deck will only be a few inches off the ground so I could use the slab method, but wouldn't using posts also follow the same principle?

I'd like to avoid having to dig down deep enough to put a joist support about half way along the deck to then lay the joists on top.

Thanks

 

[sparky23]

I have done a similar thing in my garden i had half on concrete (about 4 inches off floor level) and half on grass. On the corners i had put 4x4 post which was drilled to the floor and on the grass side i put in 4x4 post which i put into a steak (used for fence posts). drilled the joists to this, the decking is about 3m x 4.5m. in the middle i packed it out with cut off wood and slabs of paving i had lying around. i also put in noggins in the middle of each joist. The end result it is as strong as an ox, so after all that i would pack it out. hope it helps.

 

[WabbitPoo]

The simple answer is, yes more support is really needed. Assuming you are using 6" x 2" joists, even over 3.6m they will flex. You can prove that to yourself by putting one on two slabs and (carefully) standing on it.