Laying decking on an old raised patio

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Mark R

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We have a very tired and uneven raised patio of approx 40m2 in our garden that goes from the kitchen down to a retaining wall with steps. Initially we planned to install a new patio including the rebuilding of the retaining wall as it has sunk a inch or two on one side. Not including the materials, we have been quoted around 5k to get the work done (we are based in the South East). As we have incurred some extra costs recently, we think we may go down the hardwood decking route instead and save us some money.

My question is though, do I remove the existing patio slabs, which are very uneven, or do I simply place the decking frame on top with various joist supports and shims to level it? I have taken up one slab and underneath is hard compacted sand. Below this I have yet to find out.

another query I have is, if I rebuild a retaining wall, can I place the end of the decking frame simply on top and screw in some concrete screws? This is all new to me and despite having built a decked area before, it was a simple floating frame with posts.
 
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that bit of wall to the right of the first pic didnt have enough foundation, it may just continue to sink?
 
I’ve done some digging. The wall’s depth is just one brick. A mixture of hardcore, builder’s sand and soil is behind it.

Mike13 said:
that bit of wall to the right of the first pic didnt have enough foundation, it may just continue to sink?
Click to expand...

after digging up in front of the wall, I found tree roots which may have caused the failing. They are small but enough I suspect to cause trouble. We have 5 oak trees in our garden and I have already encountered tree roots elsewhere.

iOS Image - 3550335563.jpg
 
Its a low wall, so one brick deep should be ok unless the soil is weak for other reasons? But it does not seem to have a footing at the bottom? cant properly tell even from the latest picture.
 
Mike13 said:
Its a low wall, so one brick deep should be ok unless the soil is weak for other reasons? But it does not seem to have a footing at the bottom? cant properly tell even from the latest picture.
Click to expand...

Thanks. I’m going to dig a bit deeper over the weekend. I expect there to be footings, albeit compacted builders sand, as a planter in the garden I demolished made with the same bricks has this.
 
compacted buiders sand does not make a footing, it can just wash away and has no strength for any sideways load or in heavy rain.
 
Ok. I may remove the wall and replace it or at least build a retaining wall behind the current one with aerated blocks. Ideally I’d like to go with the first option as there are steps that’s are made with the same current bricks. If I remove the wall, I’ll have to remove the steps and that is more work.

Also, I’ve removed around 50% of the patio slabs as I do not want the deck to be too high. All slabs have compacted builders sand underneath them and soil below that. I’m not keen on digging numerous holes to place posts in for the frame. Instead, can I put down some concrete bedding for slabs that will support the frame?
BTW, the manholes will have hatches built! Thanks.
 
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