Definition of rising damp
Rising damp can be defined as moisture which rises up from the ground and travels upwards in the masonry of the building structure by means of capillary action. This moisture dries out on the wall surfaces and can present in various unsightly forms such as paint failure, discolouration and mould growth.
Capillaries are very narrow passages or tubes which occur in masonry. Capillary action is when moisture rises up in these tiny passages even against the force gravity.
The foundations of a standard dwelling are generally constructed of concrete laid onto compacted soil. Brick work, usually between 5 and 8 courses high is built on top of the concrete foundation. A DPC (Damp Proof Course) usually consisting of a heavy duty plastic layer is loose laid onto this. The rest of the wall is built on top of this plastic DPC layer. The section of brickwork between the foundation and DPC is designed to be a “wet zone.” The DPC is designed to prevent water from rising up beyond this wet zone. However when various factors develop and the DPC is comprised, then rising damp can take place.
The common signs of rising damp
Rising damp can occur to interior and exterior walls and usually presents in the lower portion of the wall typically up to a height of 1m. It is rare for rising damp to be higher than 1,2m. However factors such as tile cladding or a waterproof plaster applied to lower section of walls without installation of a chemical DPC can cause this occurrence.
The use of a moisture meter is sometimes used by professionals to detect rising damp, but usually the signs are very obvious and is not an absolutely necessary tool.
The usual signs and symptoms include the following:
- Paint failure characterised by blistering and bubbling of the paint film.
- Brown or darker stains or “tide” marks to the wall surfaces which is blemishes due to moisture in the wall.
- Wall surfaces feel cold and clammy.
- White powdery deposits on the wall surfaces, technically termed salts or efflorescence.
- Crumbling and failure of plaster.
- Rotting or warped skirting boards.
- Mould smell which could be occurring under skirtings or carpets and is often is triggered by damp in walls.
- Peeling or discoloration of wall paper.
- Rooms feel unusually cold in the winter months.
- Mould on wall surfaces which is usually black in colour, but can also be brown, red, green and yellow.
The causes of rising damp
There are many possible causes of rising damp and these include the following:
- DPC non existent.
- DPC has degraded and failed.
- DPC is incorrectly positioned.
- Moisture bypasses DPC via plaster from wet zone area.
- Wall below DPC has been plastered and painted, which traps moisture inside the wall.
- Ground level higher on other side of wall which breaches DPC.
- Excessive exposure of walls to rain due to design of house with no eaves or roofs with no gutters.
- Wooden floors which been removed and replaced with concrete
The detrimental effects of rising damp
There are numerous adverse effects of rising damp. These would typically include the following:
- Unsightliness. Paint failure occurs very quickly when rising damp is present and negatively impacts on the aesthetics of the building structure.
- Devaluation of property. Buyers seldom want to purchase buildings which are damp affected.
- Moisture in walls reduces insulation properties and makes buildings much colder in the winter months.
- Damp in walls can trigger mould growth which has bad odour and is detrimental to health.
- Rising damp can cause damage to property, especially to interior walls, including rotting of skirtings and carpets and rusting of metal door frames and electrical plug sockets.
