dpm as dpc or is that different?

[arcon5]

So the project is a single cavity conservatory with concrete blocks (laid flat). I've got my footings in, then two layers of solid concrete blocks to match floor level 30cm up. Floor is down with dpm and insulation so all is level.

The dpm overlaps the concrete blocks now.

I'm ready to build up my dwarf wall which is only 52cm high.

So the question is regarding DPC. The thin roll of coursing I see about, is that the same material or different? So do I need to trim the membrane as use that or just build on top of the membrane?

But then if I build on top of the membrane would I mortar 5mm below and 5mm above, or all above or what? But if the latter then what is holding the wall in place other than gravity as below the membrane and above would have no physical connection....

 

[noseall]

Standard building practice would be to sandwich both the DPM and the DPC between layers of mortar.

Yes, polythene DPM would act the same DPC in many respects and would probably be ok on its own as long as it is laid correctly. However, DPC is more robust and will tolerate greater stresses and is cheap and it would be silly to leave it out. Besides, it makes doing the corner junctions simpler too.