What's the Difference Between DPC and DPM?

Damp proofing is a key part of any new construction, ensuring the long-term health of the building by preventing issues like rot, mould growth and structural degradation. It’s crucial to make sure the right protection is adequately fitted, which is where specific products like DPC and DPM come into play.

On the surface, damp-proof courses (DPC) and damp-proof membranes (DPM) are strikingly similar. However, there are small but useful differences which dictate how and when these products should be used.

Are DPC and DPM the Same?

Ultimately, there is much more that unites DPC and DPM than divides them, both in terms of how they’re made and what role they play in property construction.

Damp proof courses and membranes serve a very similar purpose – to stop moisture rising from the ground and penetrating the structures of a building.

Both damp proofing materials come as sheets commonly made of recycled polyethylene, a very common form of plastic. As we know from discussions around reusability, plastic is not just waterproof but incredibly resistant to degradation, helping it to keep performing for the life of a building.

Can You Use DPM as DPC and Vice-Versa?

It is technically possible to use DPM and DPC interchangeably as they’re similar base materials, but it would never be recommended for reasons around their design.

Both DPM and DPC are built for very specific applications within a building; in modern construction, DPC is usually lapped with the DPM to create a continuous moisture barrier.

What are the Differences Between DPC and DPM?

While both DPC and DPM are made of similar materials and serve similar purposes, there are differences in their appearance, and some additional features, which mean they serve unique purposes.

What is DPC?

Damp-proof course is a protective layer designed to stop rising damp from entering the building’s masonry.

Masonry is particularly susceptible to rising damp due to a phenomenon called capillary action (also known as wicking), where water is attracted to narrow spaces, causing it to move against gravity and without assistance. Just as water travels up through a paper towel, it also travels up through porous building materials such as bricks.

DPC is specifically designed to be installed just above ground level within the brickwork, often within a mortar line. As a result, it is sold in thin, tape-like rolls, so it can be easily installed without having to cut large sheets of plastic. DPC can also come with additional bonding properties not present in DPM to ensure a secure hold within the brickwork.

What is DPM?

A damp-proof membrane (DPM) is a large plastic sheet designed to be laid across a large area of a building, providing a long-term barrier against moisture rising from the ground. It is usually installed either beneath or above building slabs or screed; installing it below helps protect the slab, while installing it above gives additional protection to floor finishes.

In modern construction, DPM is also run into the walls, lapping DPC to create a continuous bowl of protection for the building against any rising damp from the earth.

Because DPM protects a larger area, it is sold in wider sheets than DPC to provide as much impenetrable coverage as possible. Some DPM also comes with additional gas protections to stop things like methane and radon rising from the ground – these are often called gas membranes.

Ultimately, most projects will utilise both DPM and DPC, alongside other things such as jointing tape, vapour barriers and vertical DPC, to ensure a property enjoys long-term damp protection.