Thanks for your question on the difference between DPM (damp proof membrane) and DPC (damp proof course).
Damp proofing is a term that refers to water resistant material that is designed in order to prohibit dampness from occurring. Damp proofing a building will ensure that all general moisture does not saturate the walls. Saying this, however, there are several procedures that damp proofing must go through in order to ensure its efficacy.
One method of damp proofing is damp-proof course (DPC)
This is essentially a barrier created to resist moisture and inadvertently rising damp. This DPC layer is generally constructed below all housing walls.
The other method is damp-proof membrane (DPM)
This, on the other hand, dissimilarly to the above, is a membrane material that is designed to act as a barrier for potential moisture transmission. This can take the form of a polyethylene sheet underneath concrete.
This is the difference between DPM and DPC.
I hope it helps.