DPC in Construction: What It Is, Types & Why It Matters

DPC — damp proof course — is one of those construction terms that gets mentioned a lot but rarely explained clearly. If you own or are building a property, understanding what DPC is, where it goes, and what happens when it fails could save you from one of the most expensive and frustrating problems in building maintenance: rising damp.

What Is DPC (Damp Proof Course)?

A damp proof course is a horizontal barrier built into the walls of a building at a specific height above ground level. Its job is to prevent ground moisture from rising up through masonry walls by capillary action — the natural tendency of porous materials like brick and mortar to draw water upwards.

Without a DPC, ground moisture wicks up through the brickwork and into the wall above ground. This causes rising damp — wet patches on walls, peeling paint, efflorescence (white salt patches), mould, and eventually deterioration of plaster, skirting boards, and wall finishes. Left untreated long enough, it damages the structural integrity of masonry.

Where Does DPC Go?

DPC is installed at two critical levels:

• At the base of walls: Minimum 150mm (6 inches) above finished ground level — high enough that surface water splashing off the ground can't bridge over the top of the DPC.
• Below any floor slab that sits on the ground: A damp proof membrane (DPM) — essentially the horizontal version of a DPC — goes under ground floor slabs to stop moisture rising through the concrete.

These two elements must be linked — the wall DPC and the floor DPM must connect so there's no gap that moisture can travel through.

Types of DPC Materials

DPC in India vs the UK vs Australia

In the UK, DPC is a legal requirement under Building Regulations Part C (resistance to moisture). HDPE or polythene DPC at 150mm above ground is standard on every new build.

In Australia, AS 3700 (masonry structures) and AS 2870 (residential slabs) specify DPC requirements. Termite barriers are often combined with DPC requirements in Australian standards.

In India, IS 3067 covers damp-proofing of buildings. In practice, DPC quality varies significantly on residential builds — many contractors use a single coat of cement-waterproofing slurry rather than a proper physical DPC membrane. This is cheaper but less effective and shorter-lived.

Pro Tip: In India, specify a 1.5mm thick HDPE membrane as your DPC rather than a bitumen-slurry coat. It costs marginally more but lasts far longer and performs better. Make sure the contractor laps the DPC at corners and joints — a DPC that isn't continuous is as good as no DPC.

What Happens When DPC Fails?

DPC failure is common in older buildings and those where it was installed poorly. Signs of a failed or absent DPC:

• Tide marks (horizontal damp patches) on internal walls, typically 0.5–1.0m above floor level
• Paint peeling or blistering at the base of walls
• White salt efflorescence on internal or external walls at low level
• Mould growth at the base of walls
• Damp smell in ground-floor rooms
• Plaster crumbling at the base of walls

How to Retrofit DPC in Existing Buildings

If a building has no DPC or a failed one, there are two main retrofit options:

1. Chemical Injection DPC

Holes are drilled at regular intervals (typically 120mm centres) into the mortar course at the required DPC level. A silicone or boron-based waterproofing cream or fluid is injected into each hole under pressure. The chemical spreads through the mortar and pores to create a water-repellent zone.

This is the most common and practical method for existing buildings. It's less invasive than physical methods and works well on most brick and stone construction.

2. Physical DPC Insertion

The mortar course is cut using a masonry saw, and a new physical membrane is inserted. More disruptive and expensive than injection, but more reliable for heavily dampened walls.

DPC vs DPM: What's the Difference?

DPC Cost