DPC membrane (Damp Proof Course) is a waterproof film or strip that is built horizontally into a wall or foundation to stop rising damp from the ground. It is a key element of the moisture protection of both new and renovated masonry walls.
How does DPC membrane work?
Moisture from the ground can rise by capillary action through porous materials such as brick and mortar. This leads to damp patches, mould and salt crystals on the inside of the wall. A DPC membrane forms a continuous waterproof layer in the wall, so moisture cannot travel further upward.
The membrane is typically installed:
- Between the foundation and the wall — just above ground level
- In cavity walls — at the base of the cavity, to drain incoming moisture
- Under sills and over lintels — as a flashing to deflect water
Materials
DPC membrane comes in several forms:
- PE membrane (polyethylene) — simple and inexpensive
- EPDM — durable, flexible rubber
- Bitumen DPC — bitumen with a carrier reinforcement
- Lead — traditional, strong but heavy
- Stainless steel sheet — for special applications
Installation
When installing a DPC membrane, the following points apply:
- Continuous layer — no breaks, otherwise damp rises around it
- Adequate overlap — at joints, at least 100 mm overlap
- Above ground level — install at least 150 mm above grade
- Protect during work — avoid damage from mortar or tools
- Connect to vertical waterproofing — especially at basement walls
Retrofit
In existing buildings with rising damp, a DPC layer can be installed retrospectively. Methods include:
- Saw-cut method — cutting a slot and inserting a DPC strip
- Chemical injection — a water-repellent cream or liquid is injected
- Electro-osmosis — an electrical principle to drive moisture downward
Related terms
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