How to build a low deck over 2 surfaces?

[diymumma]

Hello. I want to build a floating deck . It will be 5.4m × 5m and connect to an existing low level deck with a step up.The deck will be partially sit on cement pad and partially on dirt. The bearer on the cement pad will sit on a mini pedestal block and then tuffblocks with stumps when it reaches the grass after approx 500mm.

Im looking to use 90x90 H4 F7 stumps with 140x45 h3 f7 bearers and 90x45 h3 f7 joists notched into the stumps and will be spaced 45mm apart. Im trying to work out how far apart i space the bearers and the tuffblocks. The calculator to work this out is beyond me and im wondering if someone is able to advise please. Also i know with tuffblocks i should bring them in with the bearer so they dont stick out under the deck. For support do i carry out side blocking of the bearers or joists. Thanks

[MitchellMc]

Hi @diymumma,

The joists will need to be supported every 1000mm, so that means the bearers are spaced 1000mm apart. The bearers, being a slightly larger calibre, don't need to be supported quite so regularly, so you could push the spacing of the stumps out to 1400mm. This isn't the max span of the timber, but it provides a good safety net to work within and ensures you have a stable and solid deck.

You might like to have a read through this helpful guide: How to build a low-level deck. Also, we have this step-by-step guide on How to build a deck.

For the side of the deck, I'd typically suggest running a framing timber along the exposed joists/bearers and screwing through it into their ends. Or, you could block them out with sections between them. Either way, it's then best to run a decking board over them for neatness.

Please let me know if you have any questions.

Mitchell

[diymumma]

Thanks that so helpful. To work with the height i want for the step up, I'd actually prefer to do a single structure i.e. instead of joists on top of bearer system i would like to do frame of 140x45 with internal joists 90x45 connected with joist hangers and noggins for additional support. Is this ok or do i need to the joist on top of bearer system for safety and strength? I will possibly be placing a pvc hampton style fence on the side of the fence so cognisent of safety.

[MitchellMc]

That would be fine, @diymumma. However, the joists will need to be supported across the five-metre span. So, for each 90 x 45mm joist, you'd need a support every 1000mm. That's at least three supports per joist. As the joists are spaced at 450mm centres across the span, you'll need around eleven of them. That means you'd need around 33 supports for your joists. Now, that's why people, if they have the room, choose to have bearers under joists, as it limits the required support.

Given your deck is partially over concrete, the amount of supports is not a huge deal as they can simply be an angle bracket Dynabolted into the concrete and bolted to the side of the joist.

Mitchell

[diymumma]

Thats great to know ill draw both options out and see what best suits. I will need to bring the frame in about 10cm to allow for the tuffblocks and the picture framing overhang. Should the sides have two 140x90 with noggins on either side or should i do the 140x90 10cm in then attach noggins with a 90x45 on the furthest outside? I believe in either option i would also need to put in noggins. Do i put noggins along every joist every meter or so and do i put them in line on every joist or stagger?. Thanks

[EricL]

Hello @diymumma 

I suggest having a quick look at this discussion - Low-level deck over concrete alfresco by @siran. It's an excellent example of a decking frame that is partially on concrete and on soil. Plus, it's also been designed with picture framing in mind. In regards to noggins, I believe that it's better to have them staggered between every joist. This will make the frame much stiffer and add extra support to the overall frame.

In regards to the sides, I suggest drawing them both in your plans and see which one would be easier to build.

If you need further assistance, please let us know.

Eric