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Welcome to the Bunnings Workshop community @dev039. It's brilliant to have you join us, and many thanks for your question about constructing a deck.
It would really help if you could share a simple sketch of your deck, showing where the posts are and how you plan to run your joists. Once we can see the layout, we will be able to give you much more accurate guidance about what needs adjusting and what can stay as it is.
There is no strict rule that posts must always be under 1.8 metres apart. The real limiting factor is the size of the timber you are using to span between those posts. If your posts are two metres apart, that is fine as long as the timber spanning between them is sized for that distance. For example, a 140 x 45 millimetre joist can span close over two metres, so that would be suitable. A 90 x 45 millimetre joist would not be suitable, because its maximum span is about 1.4 metres. I'd recommend reading through this guide on How to understand decking span tables, as it's very helpful for checking what size timber you need for your layout.
If you do have sections where the span is too long, you can absolutely use TuffBlocks to add extra support under those areas. They work well as supplementary bearers or mid-span supports.
For the levelling issue, it would be great to see a photo of one joist attached to a post so we can see exactly where things are out. Packing can be used within reason, but where and how depends on your fixing method. With a few photos or a quick sketch, I can map out the easiest way to correct the levels so you end up with a solid, straight deck.
Happy to help further, and let me know if you need a hand uploading any pictures.
Please let me know if you have any questions.
Mitchell
Hi Mitchell,
Many thanks for the advice . Sorry the posts are even more than 2 meters . Please see sketch and advice whether I can use tuffblock for more supports
( to replace required posts). Please advice .
thanks
As mentioned, 140 x 45mm timber would be suitable for your joists @dev039. However, you would need a central post or support for each joist as they can't span the full 4900mm.
Instead of individual supports, you could construct a frame that would act as a bearer for the joists of around 290 x 45mm. I've created the rendering below to show the layout. Without using a bearer, you would need each and every 140 x 45mm joist supported in the middle by Tuff blocks.
Mitchell
I'd need a few more details on what the issue with the slope is and why it has occurred, @dev039. If there is sloped ground, the posts would be installed, and then a string line and string level would be used to establish a flat plane, and then the posts would be cut to the correct height. Have the posts been installed, and are they not at the correct height? Is the frame installed, and is it sloping?
Mitchell
It sounds like the issue has begun right at the foundation @dev039. The level of any deck is set by the posts, so if the posts were not cut or set to the correct height at the start, the frame fixed to them will naturally follow the same slope. Once the frame is already attached and you are seeing a 60mm fall from one end to the other, packing out joists becomes very difficult and, in many cases, not structurally appropriate.
At this point, the more reliable solution is to correct the posts rather than trying to force the frame to compensate. The posts on the lower side will likely need to be dug out and reset or replaced so they sit at the proper height, allowing the frame to be level from the outset. It’s far better to address the issue at the base than to try a band-aid fix on the joists, especially since their orientation and how they sit in the frame may not even allow for safe packing.
I'm sorry, but starting again with the posts at the correct height will give you a straight, stable and long-lasting deck.
Mitchell
If the decking is 4900mm in length @dev039, then it would be best to cut it into two lengths of 2400mm, with a 100mm offcut, and run it in the direction of the 2400mm on the deck.
Mitchell
