Damp Proof Course Materials in Domestic Buildings – My Building Report Listed The DPC as a Major Defect?

Your Building & Pest report might talk about defects related to the Damp Proof Course material, aka the ‘DPC’. Anyone who has owned a terrace dwelling in Sydney will know all about it, but for others, let us elaborate.

It is imortant to understand that bricks and concrete are very absorbant building materials on their own (concrete less so). A house brick will suck up water like a sponge. Via cappillary action water is able to travel vertically up the masony, known as ‘wicking’. This cappilliary action can also carry dissoved minerals within the water, stuff like salts and calcium. Once in the brick, the minerals will want to come out of solution and start to crystalise inside the brickwork causing material damage. This process is refered to as fretting or efflorescence.

Various construction techniques must be employed to prevent water penetration through masonry elements.

One of the main ways to prevent ‘wicking’ is to install a waterproof material in the lower brick courses known as a damp proof course. The DPC is installed at the time of construction and usually sits just below the internal floor level. The damp proof course acts like a ‘high tide’ marker, preventing moisture being absorbed vertically any higher than the level of the dpc.

Historically different materials have been used as DPC material, and the type of damp proof course can indicate the age of the building (based on the age of different DPC practices).

Below is a rough timeline for the advancement of DPC material in Austalian domestic building codes:

Slate – Up to 1919. Commonly seen in Victorian era dwellings, slate is the most problematic / least effective DPC material. Rising damp is common-place in buildings from this period. Slate is a natural material that has a tendency to ‘delaminate’ or dissintergrate in the presence of mineral salts and water.

Bitumen / Asphalt – 1919-1931. More effective at preventing damp penetration problems, especially when coupled with cavity wall construction (which become commplace by 1905). These ‘bituminous’ DPCs were either installed in-situ or were prefabricated. Less prone to material deterioration. Some slowly melted away over time in the Australian summer, or became brittle and cracked.

Lead – 1919 -1965. More stable than its predecessors, lead was a more ‘reliable’ product that become the norm in housing developments across Sydney by the 1950’s post war housing boom. Lead is a soft metal that can be vulnerable to corrosive action under certain conditions. Personally we have not found rising damp to be an issue with lead DPC houses.

Plastic / PVC – 1967 onwards. Industrial strenght plastic obviously has many advantages over lead, asphalt and slate. By the 1970’s many plastic products were being mass produced much more cheaply. Plastic was easier to manufacture, cheaper to buy, easier to install and never failed if installed correctly. Plastic DPCs are still used today in Sydney house construction.