Damp Proof Course – the First Line of Defence
Friday, January 03, 2014
Effective damp proofing is now a regulatory requirement for all new buildings, and the first line of defence is always the damp proof course that separates the inside of a building from damp rising up from the ground and into the structure through capillary action
Rising damp hasn’t always been a big problem though. Historically, many of the materials used in buildings were very porous – soft, lime-based mortars and water-based paints which allowed the structure of the building to “breathe” naturally, any moisture evaporating into the air without causing any damage. But, with the advent of new materials, synthetic paints, linoleum, tiles and gypsum-based plaster, combined with more efficient draft proofing, the natural evaporation and movement of moist air was halted and building damp became an issue.
The term “damp proof course” got its name in late Victorian times when builders first began to appreciate the importance of creating a barrier to stop water seeping up into the structure of a building. The “course” was initially a mixture of tar and sand or a row of slate but later a course of hard engineering brick, which was impervious to water. These rows of blue/black bricks can commonly be seen on older buildings.
But in the 20th century, new bitumen-based materials and the later introduction of cavity walls, saw damp proofing technology and practice make significant advances and the humble damp proof course found its way into a range of applications throughout a building from the prevention of rising damp along a building’s foundations to halting the ingress of water around windows, doors and exterior cladding systems.
Today damp proof courses are usually inserted in outer walls at about 150mm above ground level to raise them above damp conditions caused by rainfall, etc. On the interior wall, the damp proof course will be slightly higher and usually level with the concrete floor screed. The damp proof membrane under the screed is sometime bonded to the inner damp proof course, effectively sealing the inside of the house from exterior damp.
In order to be effective, a damp proof course must exhibit a number of key properties. Firstly, of course, it must be impermeable to water, but it must also be tough enough to withstand extreme compressive forces of the brickwork above it and to resist penetration by grit or uneven brick and block work. It must be flexible too, and capable of stretching with any slight building movement without losing its impermeable properties. And it needs to achieve all this across a wide range of temperatures.
One of the biggest advances in recent years has been the introduction of synthetic rubber waterproofing membranes such as EPDM (Ethylene propylene diene monomer). This remarkable material, used by Russetts in our EPDM Strip System, meets and exceeds all the basic requirements of a damp proof course and has a life expectancy of over 40 years. As a synthetic rubber, it can be simply bonded to itself to create continuous strips and to damp proof membranes and its flexibility makes it fast and simple to install.