Shed base

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Hi guys. I'm building a shed measuring 13ft x 8ft (I know 12ft would be better for timber sizes but I am building as big as I can in the space the missus has allocated). Today I've dug down 150mm ish to the depth I want my concrete. See pictures.

The corner of the shed will be in front of the manhole. The bit of dirt next to the manhole will be later concreted and used as a bin store lean to against the shed.

20220305_173534.jpg 20220305_173543.jpg 20220305_173556.jpg

Tomorrow I'm going to B&Q to get strips of ply cut to this depth for shuttering. Do I really need a layer of hardcore? Can I throw a load of crushed stone and brick in? I've plenty to go at, that I took out of this hole! Should I use rebar? What about a whacker plate? How much would a concrete supplier charge for fibres in the mix? Will a concrete supplier deliver 1.5 cubes? There'll only be me and the missus barrowing and its 15m from the street.

My plan is to have the concrete level with the path so there's level access, and it reduces the height against the boundary. However this leaves the patio quite a bit higher than the shed base. To counter this I intend to firstly lay visqueen under the concrete, and lap it up against the patio. Then lay a course or two of breeze blocks against the patio, so the visqueen is between the blocks and the patio, thus avoiding damp. Does this sound acceptable?
 
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First thing- the sheds (b & q etc) are not the cheapest for timber. For a shed base you'd be best looking round the back of any light industrial estate for spare pallets , ask nicely & off you go.
DPM under the slab- fine, it's a good idea anyway cos it helps the concrete cure better by not drying out too quickly.
Main problem with shed bases is if they're bigger than the shed you get rainwater ponding on the slab and rotting the shed bearers. So think about that one.
Hardcore etc up to you. I've put several sheds up on council pavers direct on soil and sand so 150mm concrete is a bit OTT.
Your DPM will end up full of holes if you lay it straight on top of crushed bricks, if you do go the hardcore route you need to smack it down somehow- sledgehammer works well enough just dropped vertically and repeatedly- then top it off with sand & then stick the DPM down.
Someone in your area will have a volumetric mix wagon- perfect when you are barrowing cos it mixes a barrowload at a time and you only pay for what you use. 15m is nowt- up here you get 15 minutes plus 15 mins per cube in with the price- long as your hole is all set out and good to go it's easy, I've done 2 cube on my own at 30m before now (didn't enjoy it but it happened).
Rebar- no. Fibres- ask them if you like but don't get worked up about it. 150mm is overkill for a shed base, 100mm is normal for a garage.
 
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Thanks for your assistance on this. The only reason I got ply from B&q was because they'll cut it precisely so I can use it for shuttering. £42 a sheet certainly made me wince
 
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You really don't need a concrete pad to stand a shed on. Wack down some MOT and lay some concrete lintels across. Stand shed on these. This is what our local shed builder recommends, is what I did, and has been fine. The lintels stop water puddling underneath and keep the wooden bearers clear of the ground.
 
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You really don't need a concrete pad to stand a shed on. Wack down some MOT and lay some concrete lintels across. Stand shed on these. This is what our local shed builder recommends, is what I did, and has been fine. The lintels stop water puddling underneath and keep the wooden bearers clear of the ground.
I'm building it myself. The concrete floor is the finished floor surface. No wooden bearers.
 
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OK, in that case make sure your design stops damp entering under the walls across the top of the concrete base.
 
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If the concrete is to be the finished shed floor, and if that finished concrete is lower than the patio, you will need to be careful to keep water out of the shed. Even if you lay blocks that go above the patio height, is there not possibility of an run-off seeping under the wall sole plates? I suppose you are trying to direct the water under the base with the Visqueen. This could work if your shed roof overhangs the blocks to stop any water falling on the 'inside' of the blockwork.
 

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