Basement floor construction - minimum slab?

[Brix]

Looks like I am having to dig out my basement floor after a flood from outside and reinstate. Tanking and DPM installed about 18yrs ago have failed mostly around the bodged floor wall joint. The existing installation has criminally thin insulation which I would like to increase as much as possible. But there is no scope to raise the finished floor level (old listed building).  I have drawings of what was supposed to have been installed although I cannot be certain that it matches 100% what was installed - but hopefully not a million miles out. I'm hoping to strip back as far as the old DPM and leave the blinding/hardcore (is it negligent to reuse the blinding?).

 

Existing construction is: 

 

20mm floor finish, over

75mm reinforced screed, over

25mm UFH pipework and mesh reinforcement, over

150mm slab, over

25mm rigid insulation, over

DPM, over

50mm blinding, over

150mm hardcore.

 

Ideally I would like to end up with a new floor construction incorporating at least 100mm insulation - more if possible.

The use is just a residential basement with lightweight traffic. The only particularly heavy thing might be a 500L water tank. Floor finish could be floating floor or possibly something like polished concrete.

 

Any thoughts on this?

[Russell griffiths]

Quick response. 

Scrape off the blinding down to just a bit to fill in voids

25mm eps to squish down to protect dpm

dpm 

100mm pir

concrete floor with mesh with ufh tied to mesh. 

Grind and polish concrete. 

 

Increase insulation if you have the height. 

 

If you don’t want polished concrete then finish the concrete well, thin coat of self levelling compound and LVT floor. 

 

 

[tonyshouse]

Floating floor for me, maximise insulation, eps dpm/vb on top then floating floor 

[Brix]

OK,  looks like I don't need to take out the slab afetrall - just the reinforced screed and 20-25mm insulation layer. This is mostly 100mm overall depth (plus 21mm floor finish) - although it seems to be only 80mm in one of the three trial holes in the middle of one of the rooms. The damp contractor has specified Vandex BB75 and Drybase liquid DPM on top of the existing slab and lapped up the walls to sort out the waterproofing. 

 

So - I have 80-100mm to play with (mostly 100mm). I need to install insulation, screed and UFH on top of the slab and would like to improve on the existing 20-25mm insulation. Any suggestions? It's a domestic basement floor so not major point loads. I'll probably go with parquet floor finish on top.