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I'm having a little extension done, 4m x 4m.
It appears the ground isn't of great quality so building control are likely to ask for a raft, how much is this likely to cost me? I appreciate it will be a VERY rough estimate.
4x4x.2 equals 3.2m3.
That would be 300 quid on truck mix, bear in mind it's a cost saving as your ground floor slab is then complete.
Roll of 1200 poly 40 quid
1 layer a193 50 quid.
Your raft design may differ with thickenings and extra mesh at the perimeter.
Apparently it'll need steel re-bar's, how much does that change things by?
Your raft design may differ with thickenings and extra mesh at the perimeter.
I'd be very surprised if it didn't. Mine was about £800 for materials including rebar and thickened edges. Fully DIYed so no other costs. I reckon you could easily pay 10 times that by getting the pros in.
Bar and mesh are two different things.
Also think about the perimeter, if the raft does form your finished floor then you will see a concrete face as opposed to brickwork like you normally would. Also need to think of insulation and where it can be placed, ie not under load bearing walls.
what are the ground conditions?
If the upper ground is the rubbish soil I would have thought strip footings down to the good stuff, then slab built off the strips would be better, especially as 'extension' implies attached to your current house. Plus the appearance and insulation aspects as mentioned by wrightyson mean this isnt a simple pour concrete flat, build wall, job done situation.
Im only familiar with the south, where apart from the cambridgeshire fens, poor ground generally means clay heave rather than inadequate capacity. If you are elsewhere, then ignore me.