Different Types of Damp

There are four main types of dampness that could affect your home. It is important to understand the difference between them so that you can effectively treat the problem.

1. Rising Damp

This is caused by water rising from the ground into the home. The water gets through or round a broken damp proof course (DPC) or passes through the natural brickwork if the property was built without a DPC. A DPC is horizontal layer of waterproof material put in the walls of a building just above ground level. It stops moisture rising through the walls by capillary action.

Rising damp will only affect basements and ground floor rooms. It will normally rise no more than 12 to 24 inches above ground level (300mm to 600mm) and usually leaves a ‘tide mark’ low down on the wall. You may also notice white salts on the affected areas. Rising damp will be present all year round but is more noticeable in winter. If left untreated it may cause wall plaster to crumble and paper to lift in the affected area.

Note. Black mould will rarely be seen where there is rising damp (and then only in the early stages). This is because rising dampness carries with it ground salts which prevent the growth of black mould.

2. Penetrating Dampness

This type of dampness will only be found on external walls or in the case of roof leaks, on ceilings. It only appears because of a defect outside the home, such as missing pointing to the brickwork, cracked rendering or missing roof tiles. These defects then allow water to pass from the outside to the inner surfaces.

1 Penetrating dampness is far more noticeable following a period of rainfall and will normally appear as a well defined ‘damp-patch’ which looks and feels damp to the touch. Note. Black mould is rarely seen on areas of penetrating dampness. This is because the affected area is usually too wet and the dampness contains salts picked up when passing through the wall, which prevent the growth of black mould.

3. Defective Plumbing

Leaks from water and waste pipes, especially in bathrooms and kitchens, are relatively common. They can affect both external and internal walls and ceilings. The affected area looks and feels damp to the touch and remains damp whatever the weather conditions outside. A quick examination of the water and waste pipes serving the kitchen and bathroom and the seals around the bath, shower and sinks; plus the external pipework, such as guttering will usually find the source of the problem.

Note. Black mould will rarely be seen on this type of dampness because the area is usually too wet and the chemicals in a waste water leak will prevent mould growth.

4. Condensation

This is by far the most common cause of dampness experienced by tenants and householders, resulting in a large number of enquiries or complaints received by the Council. Condensation is caused by water vapour or moisture from inside the dwelling coming into contact with a colder surface, such as a window or wall. The resultant water drops (condensation) may then soak into the wallpaper or paintwork or even plasterwork. In time, the affected damp areas then attract black mould that grows on its surface.

Condensation mainly occurs during the colder months, whether it is rainy or dry outside. It is usually found in the corners of rooms, north facing walls and on or near windows. It is also found in areas of little air circulation such as behind wardrobes and beds, especially when they are pushed up against external walls.

Note. Black mould is frequently seen on this type of dampness. Note. Black mould is frequently seen on this type of dampness

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