Extension floor

[cjames]

Building new single storey extension need advice on the following:
How far to dig down for the new floor and how would you build it back to floor level and what materials should I use.

 

[noseall]

on a typical extension i would:

dig off surface material (oversite) to a depth of 425mm.

lay 100mm mot stone (30mm-dust) and compact with vibrating roller or compacter plate.

sand blind the stone, approx 25mm.

lay 1200 gauge visqueen dpm turning edges into dpc.

fit 125mm jablite floor insulation.

lay 500 gauge dpm over jablite only.

lay 100mm concrete slab and tamp finish.

lay 75mm floor screed.