Deck joist support question

7 Nov 2006
Reaction score
United Kingdom
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 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.

Sponsored Links
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. :)
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.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links