There are three main types of damp:
- Rain penetration
- Rising damp
Structural dampness refers to the presence of unwanted moisture in the structure of a building, either as the result of intrusion from outside or condensation from within the structure.
A high proportion of damp problems in buildings are caused by the "big three":
Rising dampTrue rising damp is rarer than commonly perceived and is regularly misdiagnosed.
Rising damp occurs when water enters a structure through the pours in the masonry, the mortar beds are normally the most absorbent part of the wall, allowing damp to rise in an upward movement by capillary action from below the ground. This process occurs when water molecules are electro-chemically attracted to mineral surfaces.
Rising damp occurs when water is sucked up into masonry from the ground - in the same way that a sponge placed on a wet surface will absorb water. Most houses have a "damp proof course" - a layer of material impervious to water that is placed in the wall during construction and acts as a barrier to rising damp. If the damp proof course has failed, or was never included when the walls were built, then rising damp can result.
Externally, mortar may crumble and salt stains may appear on the walls. Steel & iron wall ties may rust, in extreme cases, mortar or plaster may fall away from the affected wall.
Internally, decayed skirting boards, crumbling plaster, deposits of salts, peeling paint and wallpaper are common problems associated with rising damp. It may also be the cause of poor indoor air quality and respiratory illness in occupants.
However, rising damp can often be misdiagnosed and is not as common as other forms of damp, factors such as the wall thickness, porosity of the brick or stone and mortar joints should all be taken into account, and a thorough investigation into the type of dampness must first be established.
Penetrating dampPenetrating damp due to a leaking roof, or through defective mortar joints / pointing. This occurs when water penetrates and soaks through a wall. The most common causes include external construction defects such as defective guttering, rainwater pipes that leak at the joints and continuously soak the walls or as rain spills over the guttering, cracked rendering and defective or missing sealant between windows and walls.
Damp patches on the floors, ceilings or walls can appear and the long term effects include damage to decoration and decay to timber and plaster. Unsightly black mould growth may also form.
Rain penetration is most often associated with single-skin walls, but can also occur through cavity walls - e.g. by tracking across wall ties, or in stone walls where the cavity is blocked by rubble or mortar droppings.
Other common defects include:
- Roof defects such as faulty flashing, cracked or missing slates or tiles
- Faults in the brickwork or masonry such as missing or cracked pointing
- Porous bricks and porous sand stone
- Missing or defective mastic around windows and doors
- Blocked weep holes
- Missing or defective trays in cavity walls
CondensationCondensation is arguably the most common form of dampness, with at least 1 in 5 homes in the UK affected. Tell-tale signs of condensation include streaming running windows and walls, deterioration in decoration such as discolouring of window reveals and frames, and eventually the growth of black mould.
Condensation is often caused as a result of poor ventilation and modern living and lifestyle issues. Modern housing and in particular older housing which has been improved and modernised, is often not well ventilated.
Many older homes once had open fires for heating and cooking. Open fireplaces take large amounts of oxygen from rooms as they burn, and air is constantly drawn up the chimney and is replaced by fresh air drawn in through old draughty windows and doors. The air drawn into the fire or stove contains the moisture vapour and humidity that we create, from every day living, breathing, cooking, washing and drying clothes - the air from outside the house is much dryer than inside the home, so older houses would reach a balance, whereby excessive moisture vapour and humidity did not build up as much as we see today.
In addition, older generations consumed much less water, and used the bath once a week, power showers were not used, so there was not that much humidity created from the bathroom; even with a larger family.
Click here to read more about the causes of condensation and black mould, including
condensation on windows - and how to solve the problem.
We offer a tailor made and bespoke solution for your home. Simply looking at one aspect of your home in isolation can lead to an incorrect diagnosis, but by taking a “whole house” approach we have the experience to recommend measures that are right for your home.
The Home Improvement Advisory Service have specialised in curing damp and condensation problems in thousands of homes across the Yorkshire for over twenty years.
Established in 1993, we are independent and provide expert help and advice.
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