I'm intending to incoroporate an outhouse into the main property. It already has a concrete floor -unsure of whether there is any damp proofing below. I need to raise the floor by 200mm to bring it level with the main building and obviosly incorporate a damp proof membrane. Are they any alternatives to pouring in 200mm of concrete. Should the membrane be incorporated into the be on top of the existing floor with the concrete or alternative infill above it ?
You can get insulation boards from your local builders merchant that are for this. I think they are about 2inch thick but I don't see why you can't use more than one layer, just lay couple inches concrete or screed on the top. The boards double up as damp proofing (you will probably need some kind of DPM in the walls as well though. Can't remeber the name of the product I know Jewson sell it though.
You can insulation boards from Jewson that can be used for this, Just pack up to the required height and put a couple of inches of concrete or screed over the top. They meet regs for DPM so no need for a separate on, should help keep the room warm too.