DPC - Damp Proof Course Q6 - Estate Agent's Examination Part 1&2

Q.
a) Explain the functions of Damp Proof Course and by using diagrams, explain the methods in which damp proof course are used. (10 marks)

b) State the material used for damp proof course commonly used in construction work. (15 marks)

(25 marks, Q6 2012)

A.
A damp-proof course (DPC) is a barrier in a masonry wall designed to resist moisture rising through the structure by capillary action such as through a phenomenon known as rising damp. The damp proof course may be horizontal or vertical.[2] A DPC layer is usually laid below all masonry walls, regardless if the wall is a load bearing wall or a partition wall. A plastic membrane is called Damp Proof Membrane (DPM).

A DPC is a durable, impermeable material such as slate, felt paper, metal, plastic or special engineered bricks^[5] bedded into the mortar between two courses of bricks or blocks. It can often be seen as a thin line in the mortar near ground level. To create a continuous barrier, pieces of DPC or DPM may be sealed together. In addition, the DPC may be sealed to the DPM around the outside edges of the ground floor, completely sealing the inside of the building from the damp ground around it.

Methods in which DPC are being used in masonry wall:

In a masonry cavity wall, there is usually a DPC in both the outer and inner wall. In the outer wall it is normally 150 millimetres (5.9 in) to 200 millimetres (7.9 in) 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, (under a suspended timber floor structure), or, with a solid concrete floor, it is usually found immediately above the floor slab so that it can be linked to the DPM under the floor slab. This enables installation of skirting boards above floor level without fear of 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, (albeit an angled section), which fits neatly across the cavity and slots into both walls (a cavity tray). This method requires the need for weep vents to enable rainwater ingress to drain from the cavities otherwise rising dampness could occur from above the DPC.

Concrete walls and floors

Concrete normally allows moisture to pass through so a vertical damp proof barrier. Barriers may be a coating or membrane applied to the exterior of the concrete. The coating may be asphalt, asphalt emulsion, a thinned asphalt called cutback asphalt, or a rubber polymer.[6]

Membranes are rubberized asphalt or epdm rubber. Rubberized products perform better because concrete sometimes develops cracks and the barrier does not crack with the concrete.