What Is a DPC? — Damp Proof Course Explained

Definition

A DPC (Damp Proof Course) is a horizontal barrier built into the walls of a building to prevent moisture from rising up through the masonry by capillary action. This phenomenon is known as rising damp. The DPC is typically a strip of impervious material installed in the mortar course at least 150 mm above finished external ground level, as required by Building Regulations Approved Document C.

When Is It Used?

A DPC is required in all new masonry construction under the Building Regulations. It is also relevant when extending existing buildings, building garden walls, and when diagnosing and treating damp problems in existing properties. DPCs work in conjunction with DPMs (Damp Proof Membranes) in floors to create a complete barrier against ground moisture. In cavity wall construction, cavity trays act as DPCs above openings.

Key Facts

• Must be minimum 150 mm above finished external ground level (Building Regs Part C)
• DPCs have been a legal requirement since the Public Health Act 1875
• Modern DPCs are polyethylene sheet, typically 450 mm or 600 mm wide
• Chemical injection DPCs use silicone cream or resin injected into drilled holes at 120 mm centres
• The DPC must be lapped at corners and joints by at least 100 mm
• Common causes of DPC failure: bridging by raised ground levels, render, or paths
• Electro-osmotic DPC systems are not recommended by most independent surveyors
• A DPC should never be covered by external render - a bellcast bead should terminate the render above the DPC

Related Calculators

Use the Mortar Calculator for below-DPC mortar mixes, or the Brick Calculator for walling quantities. The Damp Proofing Calculator helps estimate treatment costs.