Decking joists on concrete beams for low decking?

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Hi,

I'm planning a decking patio. 6.5m wide (decking running across the width), 2 to 2.6m long (joists running this way). The joist spacing will be 400mm so there will be 14 joists wide.

I'd considered using risers/pedestals - the really low ones - as I have a level access patio door (new build) so don't have lots of depth. Using 100mm timbers I was looking at having the pedestals 600/700mm apart which would result in a matrix of nearly 70 risers - which seems bonkers! I don't want to use timber posts as the ground is quite damp.

I wondered whether it might be easier to make 4-5 long concrete cast beams in contact with the well compacted type 1 MOT under the current patio slabs. I could dig small holes along the length to act as piers/footings, lay a length or two of rebar in there and cast in one go. Then the joists could run across those.

My question is: does this seem mad?!

Thanks in advance!
 

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In my view it’s a mad scheme fraught with potential problems and is just way more work! Risers are not expensive in grand scheme - 3-4£ each probs. So buy the risers, build your grid frame on top. Level it all up in situ as required with tweaks to each riser until it’s all just so. (Remember to have a slight run 1:80 ish to let rain run off) Then screw those deck boards down - and it will be done in a jiffy.
 
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Fair enough pal. Do you reckon the wider base risers like:


Could go directly onto the old compacted hardcore or is it going to need slabs laying down for stability and the use of a decking cradle like

https://www.roofingsuperstore.co.uk...ble-decking-cradle-less-than-50mm-joists.html

??
 
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Those pads will be be fine directly onto well compacted hardcore. But sure if you have old slabs kicking about you can place underneath as a bonus.

No need for the decking cradles. Put in plenty dwangs to keep your frame tight and secure.
 

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