Damp proof membrane

Hi All
Having conservatory built to replace old one. Supplier/ builder has retained old floated, and uninsulated concrete base and sunk footings around it to extend size. So at the sides outer skin is built on new footings whilst inner skin sits on concrete raft. The idea then is to lay DPM over concrete then layer of jablite upon which a chip board floor will be floated.
However before floor is laid supplier/builder wants to plaster walls. I have questioned this as I think DPM and floor should be built then plaster down to it. How can you lay the DPM after the plasterer has done his bit as the Pamp proof membrane has to lap up the sides and extend to the damp proof course or beyond or does it??.
He says it is not necessary for the DPM to reach the damp proof course.
This don't sound right to me so before I have words can anybody set me straight?
Any advice much appreciated.

so, the builder is using the old base to deal with the internal blockwork footings.
ho hum.

upon which he will lay membrane plus insulation. with ya so far.

so, all he needs to do is lay a course or two of engineering bricks upon the slab first.

lay the dpm lapping onto these bricks.

lay the insulation on the dpm and cast the floor slab.

then lay his dpc on top of the lapped dpm, build the internal blockwork THEN plaster the walls.

whatever he does i would not consider using the internal slab as a footing but that's just me. it is a connie after all and exempt from reg's.

your call.

Thanks for reply
The builder is not lapping the DPM over the course with the DPC but is lapping it up the sides to the DPC level.

But in other words the DPM question is fairly pointless as the whole build is a cowboy operation then?
The previous conservatory we had, had both internal and external walls built on the raft. The slab is about a foot thick at the exposed edges and they sunk the footings around it by another foot depth minimum.
I assumed this would be O.K as I assumed external walls would be bearing the load.
Surprised, as the company we are using we chose on recommendation and they have a good reputation locally.
Might resort to an independant surveyor for peace of mind then
Ta once again.