No damp course under quarry tiles

[jobdone]

Can any give me some advice on how to deal with a problem with a floor in a Victorian house.
The quarry tiles have been lifted and the customer wants to keep the floors level when finished. Here lies the problem as insulation board and ufh (electric) is going down well which means excavating the screed which is only about 25mm then just rubble.
I'm thinking of removing floor plus rubble then sand blinding. Adding dpm insulation board then screeding.before adding insulation board heating cable and latex. I'm fine with all this the bit I can't get my head round is where does the moisture from the floor go? I'm concerned about it being pushed into the walls.
Long winded but I think I'm there.

 

[Bill]

Try a liquid DPM over the existing base, this will help minimise height constraints. This should only add 12mm to 18mm from where you are now.

 

[Bond]

A couple of thoughts, semi-dry screed. Or If it’s a smallish area, you could bed 600 x900 precast concrete paving slabs, tape joints and tank. Then add your insulation boards etc. ( not conventional l know).