Damp-proof course


Damp-proof course

A damp-proof course (often abbreviated to DPC) is a horizontal barrier in a wall designed to prevent moisture rising through the structure by capillary action - a phenomenon known as rising damp.

Building standards in many countries require most new buildings to incorporate a DPC at the time of construction. This may consist of a thin strip of plastic, a course of engineering brick or slate, or a layer of bitumen.

Where a DPC is absent or inadequate, there are various means of retrospectively fitting one. A common method in masonry walls is to drill holes into the wall at regular intervals and inject a penetrating chemical (e.g. silicone) into the holes. The chemical is absorbed into the masonry where it dries to form a waterproof barrier. Some irregular stone walls cannot be drilled for a chemical DPC, so an osmotic electrical system is often fitted.

Alternatively the cement joints can be drilled and the chemical injected there instead, although this is a less satisfactory method. A larger volume of chemical will be needed.

Some forms of the chemical are odour free, some have a strong odour, this should be taken into account when purchasing.

A Damp Proof Membrane (DPM) performs a similar function for a solid floor.

Construction

The DPC known as Damp Proof Course is usually a thick black plastic strip bedded into the mortar between two courses of bricks or blocks. It can often be seen as a thin black line in the mortar near ground level.

A DPM is usually a thick polythene sheet laid under the floor slab, to allow the slab dry out and keep out groundwater. It is often laid on a bed of sand, to prevent the sharp edges of the damaging it.

To create a continuous barrier, pieces of DPC or DPM are welded together. In addition, the DPC is welded to the DPM around the outside edges of the ground floor, completely sealing the inside of the building from the damp ground under it.

In a cavity wall, there is usually a DPC in both the outer and inner wall. In the outer wall it is normally 150-200mm above ground level (the height of 2-3 brick courses). This allows rain to form puddles and splash up off the ground, without saturating the wall above DPC level. The wall below the DPC may become saturated in rainy weather. The DPC in the inner wall is usually below floor level, so that it can be welded to the DPM in the floor, and so that skirting boards can be fixed to the wall above floor level without puncturing it. Alternatively, instead of fitting separate inner and outer DPCs, it is common in commercial housebuilding to use a one-piece length of rigid plastic, which fits neatly across the cavity and slots into both walls.

In old buildings there may be a DPC made from lead. The DPM may be non-existent, leading to damp problems, or it may rely on an impermeable floor finish such as ceramic tiles to keep most of the damp out.

Health and Safety

Besides lead sheet, some DPC Materials contain asbestos fibre such as common older grey sealant and flexible tar board.


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Look at other dictionaries:

  • damp-proof course — damp proof courses N COUNT A damp proof course is the same as a damp course …   English dictionary

  • damp-proof course — damp proof .course n BrE a ↑damp course …   Dictionary of contemporary English

  • damp-proof course — noun a course of some impermeable material laid in the foundation walls of building near the ground to prevent dampness from rising into the building • Syn: ↑damp course • Hypernyms: ↑course, ↑row * * * damp proof course noun A damp course • • •… …   Useful english dictionary

  • damp-proof — adjective impervious to damp. verb make impervious to damp by using a damp course …   English new terms dictionary

  • damp course — (also damp proof course) ► NOUN ▪ a layer of waterproof material in a wall near the ground, to prevent rising damp …   English terms dictionary

  • Damp (structural) — For other uses, see Damp (disambiguation). Detail showing some of the causes of damp penetration Structural dampness refers to the presence of unwanted moisture in the structure of a building, either the result of intrusion from outside or… …   Wikipedia

  • Damp proofing — A damp proofing barrier Damp proofing in construction is a type of waterproofing applied to building foundation walls to prevent moisture from passing through the walls into interior spaces. A damp proof course (often abbreviated to DPC) is a… …   Wikipedia

  • damp course — noun a course of some impermeable material laid in the foundation walls of building near the ground to prevent dampness from rising into the building • Syn: ↑damp proof course • Hypernyms: ↑course, ↑row * * * noun : a damp resisting layer in a… …   Useful english dictionary

  • damp — adj., n., & v. adj. slightly wet; moist. n. 1 diffused moisture in the air, on a surface, or in a solid, esp. as a cause of inconvenience or danger. 2 dejection; discouragement. 3 = FIREDAMP. v.tr. 1 make damp; moisten. 2 (often foll. by down) a… …   Useful english dictionary

  • damp course — (also damp proof course) noun Brit. a layer of waterproof material in the wall of a building near the ground, to prevent rising damp …   English new terms dictionary


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