Damp Proof Course (DPC)
/ damp pruːf kɔːs /
Also known as: DPC, damp course, moisture barrier
Definition
A damp proof course is a horizontal impermeable barrier built into the base of a masonry wall, typically 150 mm above finished ground level, that prevents ground moisture from rising through the wall structure by capillary action - a process commonly referred to as rising damp.
DPCs are most commonly made from flexible polymer sheet (low-density polyethylene), but older buildings may have slate, engineering brick, bituminous felt, or lead courses. In cavity walls, a vertical DPC is also installed at window and door reveals to prevent water crossing the cavity.
In practice
During new construction the DPC is laid as a continuous strip across the full width of the leaf, with lapped joints at corners and junctions of at least 100 mm. It must be positioned so that external ground levels and any paving or render cannot bridge it - this is one of the most common installation faults inspected by Building Control.
In existing buildings, a failed or absent DPC can be remedied by injecting a silicone-based cream or fluid into a series of closely-spaced holes drilled at low level - a process known as chemical DPC injection. Physical re-installation (saw-cutting a new slot and inserting sheet DPC) is less common but more reliable for thick walls.
Building Regulations
Approved Document C requires all new masonry walls to incorporate a DPC. The guidance also covers the requirement for a DPM (damp proof membrane) in ground-bearing floors, which must lap with the wall DPC to form a continuous moisture barrier around the building envelope.
Full Building Regulations guidanceRelated Calculators
Damp Proof Membrane Calculator