Garage floor

I am proposing to convert the rear of my garage into a kitchen and currently have an enquiry in at the planning dept to asseertain whether permission is required (no external alterations).
However, even if permission is not granted I would like to put the floor down as the exisitng floor is compacted earth. Prior to firing off a query to the bulding regs people I was proposing:
Dig down and isnstall: (From information received in the pub) !!
DPM (brought up to wall dpm) 100mm Jablite vapour barrier 100mm slab screed
Does this sound about right. (100mm slab sounds a lot to me). Secondly, all my previous concrete work has been ouside where expansion joints are needed. As this will be in a frost free environment will I still need expansion joints? The area is 4.4 x 2.5 m I was thinking of just putting shuttering round the edges for tamping. Any ideas or suggestions anyone.
Many thanks.
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