What Causes Rising Damp?
Few structural problems are more worrying for homeowners than rising damp. Fixing it can be expensive, and leaving it alone results in mould and severe structural damage.
But rising damp is also often misdiagnosed, sometimes accidentally, sometimes by cowboys overcharging for a damp problem which may have a far simpler cause.
If you understand how rising damp occurs and how to spot it, you’re less likely to have to wool pulled over your eyes by unscrupulous damp “experts”.
How does rising damp occur?
Bricks are porous, which allows them to “breathe”, releasing moisture during the day and absorbing it during night.
This breathing of moisture regulates the temperature and humidity in a building, making it ideal for our changeable climate in the UK.
Their sponge-like structure also allows mortar to adhere tightly to the brick, locking them in place far better than if they were a smooth, hard material.
But their greatest strength is also their weakness. If water is being absorbed at a faster rate than it can be released, the bricks will become wet and vulnerable to salt damage, which may lead to damp spreading inside the house.
Excess water can come from driving rain, leaky gutters, cracks in the masonry or from the ground.
Rising damp occurs when bricks suck up water from the ground (also known as capillary action), allowing damp to build up in basement or ground floor walls.
Stopping moisture from being sucked up into walls has been a problem for builders since building began. The solution is to build a damp proof course into the wall.
What is a damp proof course?
Since 1875, all houses built have been required by law to have a damp proof course (DPC).
At first, a DPC was a layer of hard, non-porous stones such as slate or flint which acted as a barrier to stop groundwater from being soaked up into the bricks above.
Today’s damp proof courses are made from PVC plastic, which lasts longer, is more effective and easy to install than the traditional stone method. Low absorption bricks are also used in situations where a plastic PVC isn’t suitable.
While the law has required a DPC to be built into homes since 1875, actual enforcement of that law and general building standards were far less strict in the past.
Age, shoddy workmanship or a complete lack of a DPC has resulted in many period homes suffering from rising damp.
Improved building techniques mean rising damp is less common in modern homes, but it can still arise if design is poor or groundwater levels weren’t taken into account.
If your building is suffering from rising damp, it’s a problem which won’t go away without either fixing or replacing the failed damp proof course.
How can I tell if I have rising damp?
Because rising damp can be expensive to fix, it’s important that it is accurately diagnosed. Many other forms of damp have similar symptoms, such as lateral damp or damp caused by a leak.
If discolouration of the wall starts at the floor and has a clear stopping point with a white line of salts (called a tide mark), it’s likely that you have rising damp.
These salts are carried up from the ground and make the damp problem even worse as they continuously absorb moisture from the air.
Paint and plaster in the affected area can bubble, peel and crumble, and skirting boards may rot. There is usually an obvious smell of damp in the air and mould on the walls.