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Hi,
We're planning to replace our sloped concrete in our back patio with a retaining wall. We're looking to do it using concrete sleepers as we're under the impression that we can attach the existing timber patio posts to the tops of metal C/H section posts using the same brackets as you would with timber fence posts.
The height of the wall will be 0.6m
The height of the timber patio posts will be 1.6m, from the top of the wall
The wall will be 1.6m from the pool
My question is, do typical retaining wall instructions apply? (For example, are 1.2m C/H posts going to be long enough?) Or is this something we would need to consult someone qualified on?
Hello @Tori
Welcome to the Bunnings Workshop community. It's sensational to have you join, us and thanks for sharing your question about your retaining wall.
The footing of the retaining wall metal post must be independent of your patio timber posts. This is to make sure that no weight or stress is being applied to the patio posts. Although the weight being held back by the retaining wall is not that heavy there is still some weight there and your patio posts were not designed to hold or anchor that much weight. I propose building the retaining wall before the patio post, in this manner it will have its own independent footing.
I would recommend engaging the services of a professional driveway/pathway specialist so that your new walkway slab is built properly.
Let me call on our experienced members @Noyade, @Dave-1 and @Nailbag for their recommendations.
If you need further assistance, please let us know.
Eric
Afternoon @Tori
A do agree with both @EricL and @Nailbag There are a lot of factors that come to mind, support the roof while doing the job is the first one that raised my eyebrows at how to.
If you decide to do it yourself then here are some suggested pathways and they all require a large chunk of work.
I would start by supporting a section of your roof with props (say the far end) then remove the concrete from under the post down to the ground (allowing for a new slab) Maybe do across the house width in 3 or 4 sections and slowly work your way across and concrete each section then re-install a new longer post into a stirrup.
Once you have your slab done and the roof supported (id also suggest to factor in a surface grill drain near the new retaining wall yet to be built)
Then you can start with excavating the area where the retaining wall is to be built. I would follow the instructions and warns that @EricL has mentioned about not attaching anything to the retaining wall. It has one job and can do it well if allowed 
Before you backfill your completed wall I would suggest a large socked ag pipe be installed at the base. Easy to do at that point and will solve a load of water issues potentially later on. Some nice outside lighting could also be considered?
Main concern is supporting the roof while working on it as its a slopped concrete surface.
Dave
