Problem with screed floor

[plugy]

Morning all and happy new year, new this out of the way here is my question.
We want to convert our attached garage into a living space. The garage floor is 100mm lower than the inside floor, would it be possible to put a course of brick across the doorways (will have to have new shorter doors) and float a floor over the garage raft? if so would you need another DMP under it as technically it has already got one? Also again if possible at this depth would it have to be a wet floor or would 100mm screed be too much? Could I even reduce the amount of finish by adding insulation under the floor?

 

[23vc]

You can do 100mm screed
Does the existing dpm lap up the wall to the new floor level? If not may want new dpm under screed

 

[^woody^]

What about the insulation?

 

[plugy]

The garage floor is a raft, (overengineered about 10inch thick,) under the raft it has the Damp proofing and 50mm insulation. Straight of the slab the internal blockwork is constructed with 4in damp straight of the slab (again probably didn't need it technically as the slab already has a DMP). So could i assume even though we it already has a dmp we should install another over the existing slab, then 50mm floor insulation, then 50mm sand/cement screed? Although would 50mm be enough, would it not crack with insulation underneath due to a little give in the product?

 

[^woody^]

No need for double DPM.

If the insulation is flat and supported by the slab, 50mm screed won't crack or - spend the DPM money on a roll of 25mm chicken wire.

But on the basis of more insulation is better, consider fitting more and laying cupboard flooring on top, or on joists.

 

[plugy]

So could i assume that i would be able to lay 50mm insulation then 50mm screed without a DPM as the raft has one? We are also looking at installing bi-folding doors in the garage, would it be easier to install then screed upto the cills?