Damp Proof Course (DPC): Meaning, Thickness and Materials
Damp proof course (DPC): a DPC is a thin waterproof layer laid across the full thickness of the walls at plinth level. It stops moisture in the ground from soaking up into the walls (rising damp). In Indian houses it is most often a 40–50 mm layer of cement concrete (about 1:1.5:3 or 1:2:4) with a waterproofing compound, often finished with a coat of hot bitumen. It is commonly placed at least 150 mm above the finished ground level, and it must be continuous: one gap lets damp through.
Damp patches, peeling paint and white salt marks along the bottom of walls are among the most common complaints in Indian homes, and in many cases the cause is a missing, broken or bridged DPC. It is a cheap layer to lay during construction and an expensive one to fix later. This guide explains what a DPC is, where it goes, the usual materials and thickness, and how damp gets past it.
Last updated: 25 October 2026
What is a damp proof course?
Brick, block, mortar and concrete are porous. Water in the ground climbs up through their fine pores by capillary action, the way a cloth wicks up water. Without a barrier, a wall can stay damp to a height of about a metre. The water also carries salts, which crystallise on the surface as white powder (efflorescence) and break down plaster and paint.
A damp proof course is a continuous horizontal barrier that cuts this path. It is laid on top of the plinth, under the first course of the walls, across their full thickness. For where it sits among the other parts of a house, see parts of a building.
Where is the DPC placed?
- At plinth level, on top of the plinth masonry or plinth beam, under all walls: external and internal.
- Above ground: commonly at least 150 mm above the finished ground level outside, so rain splash and puddles do not reach above it.
- Continuous: across door openings (under the threshold), at corners and at junctions between walls, with no gaps.
- Linked to the floor: the ground-floor slab or its waterproofing should meet the DPC, so damp cannot pass around it into the wall.
- Vertical DPC is added where the floor inside is lower than the ground outside, or for basement walls, to stop moisture coming in from the side.
In an RCC framed house, the DPC is laid on top of the plinth beam. Dense concrete slows moisture, but a plinth beam can still crack and wick water, so the DPC is still needed.
DPC materials and thickness
| Material | Typical thickness | Notes |
|---|---|---|
| Cement concrete (about 1:1.5:3 or 1:2:4) with waterproofing compound | 40–50 mm | The most common in India; dense, strong and easy to lay on site |
| Hot bitumen coat over the concrete | One or two coats | Applied after the concrete has cured and dried; adds a waterproof film |
| Bitumen felt or membrane sheets | A few mm | Flexible; laps must be sealed; can squeeze out under heavy loads |
| Mastic asphalt | About 20–25 mm | Very waterproof; needs skilled hot application |
| Polythene (LDPE) sheet | Thin sheet | Cheap and waterproof; easily torn; laps must overlap well |
| Stone slabs or dense bricks in cement mortar | One course | Traditional; joints are the weak points |
The cement concrete DPC is a kind of rich, dense PCC. It should be compacted well, kept level, and cured like other concrete; see curing of concrete. If bitumen is applied, let the concrete dry first so the bitumen sticks.
How damp gets past a DPC
- Bridging by soil: garden beds, backfill or a raised pathway built up above the DPC level outside.
- Bridging by plaster: external or internal plaster carried continuously from below the DPC to above it. Many builders stop plaster at the DPC or use a groove or drip there.
- Raised paving or flooring outside that ends up level with or above the DPC.
- Gaps: the DPC left out at door openings, broken by pipes, or not joined at corners.
- Cracks in a concrete DPC from settlement.
- Leaks, not rising damp: plumbing leaks, rain penetration and condensation also cause damp patches and need different fixes.
Fixing rising damp in an existing house
If a house has no DPC, or a failed one, the usual options are:
- Remove the bridges first: lower soil and paving outside to well below floor level, and slope it away from the wall.
- Improve drainage around the building so water does not collect against the walls.
- Chemical DPC: a water-repellent liquid or cream injected into drilled holes along a mortar bed near the base of the wall, which forms a barrier inside the wall. Results depend on the product and workmanship.
- Re-plaster correctly: remove salt-contaminated plaster to above the damp line, let the wall dry, and re-plaster with a suitable mix. Painting over damp only hides it for a while.
Get the cause confirmed first. Damp from a leaking pipe or a blocked rainwater outlet will not be cured by a new DPC. For which plaster suits damp-prone walls, see cement vs gypsum plaster.
Site checks when laying the DPC
- The DPC level is checked against the finished ground level outside, which is often raised later by paving.
- It covers the full wall width, including at door openings, and is continuous at corners and junctions.
- The concrete mix, waterproofing compound and thickness match the specification.
- The top is level and finished smooth; it is cured, then bitumen is applied if specified.
- No pipes or conduits break through it without being sealed.
Hindi terms used on site
On site it is simply called “DPC” (“DPC daalna” means laying the DPC). In Hindi, a DPC is a नमी रोधक परत (nami rodhak parat), a moisture-blocking layer. Dampness in walls is सीलन (seelan), and the white salt deposit is often called शोरा (shora). Plinth is कुर्सी (kursi) and bitumen is डामर (daamar).
FAQ
What is DPC in construction?
A damp proof course: a continuous waterproof layer at plinth level across the full width of the walls that stops ground moisture rising into them.
What is the thickness of DPC?
A cement concrete DPC is usually 40–50 mm thick, often with a waterproofing compound and a bitumen coat on top. Sheet membranes are much thinner.
Where should DPC be provided?
At plinth level under all walls, commonly at least 150 mm above the finished ground outside, and continuous across openings and junctions.
Is DPC needed if there is a plinth beam?
Yes, it is still good practice. The DPC is laid on top of the plinth beam, which can crack and pass moisture.
Why are my walls damp at the bottom even with a DPC?
Usually because the DPC is bridged by soil, paving or plaster, has a gap, or the damp comes from a leak or rain rather than the ground.
Related guides: Parts of a building · Plinth beam vs tie beam · Plinth area · Curing of concrete · All construction guides
Disclaimer: Educational only. DPC level, materials and thickness should follow your architect’s specification and the relevant IS codes. Have persistent damp investigated before choosing a remedy. Disclaimer
Tanmay Arora, is an Architect with an experience of 13+ years. He is a Management Grad with a post Graduate Diploma in Building Construction and Materials. Tanmay has worked with renowned firms. He has graduated in Bachelor of Architecture. His deep interest in Architecture and Civil Engineering and his experience has made him one of the best architects a client can think of.
