Damp can affect any home and, with the obvious health and comfort issues, it is always wise to spot any problems early and remedy them quickly. Here's what to look for.
By Steve Hodgson
One of the most frequent problems encountered in the home is damp. Each year, the average home in the UK copes with around 25,000 gallons of rain water, so it is no surprise that damp can become a big problem for many.
Although most damp problems are much less serious than they actually look, whatever the cause, damp can be very bad for our health. From aggravating respiratory problems to encouraging the emergence of mites and mould, the effects of damp can be serious, not to mention making the whole property cold and unappealing.
In many cases, damp can be unwittingly encouraged due to poor maintenance. There are several causes of damp in the home, but all can be remedied. Damp can be in or around the roof, walls, floors, windows, doors or pipe-work on any property. Often, if there is a damp patch visible inside the home, the cause can be identified from an issue on the exterior. For instance, a wet patch at the top of a wall might be due to a leaking gutter outside.
So let's look at the main damp causes:
Rising damp is water from the ground that enters a structure by capillary action. Water that enters or affects a building through any other route can move about in various ways but is not rising damp. Only rising damp can be cured by the installation of a chemical damp proof course.
Rising damp has been a relatively commonly encountered problem in some types of building; however, it is often misdiagnosed. It is important that the investigations into dampness are undertaken by a trained and competent surveyor who can recognise and understand the problem. We would always recommend that the surveyor who undertakes investigations has been awarded the CSRT qualification.
Most types of masonry used in the walls of buildings will allow some water movement by capillary action; however, this is usually controlled by a physical barrier or damp proof course. If this physical barrier is absent, has broken down or is damaged then it is often possible to install a remedial damp proof course (DPC) to control water rising from the ground.
Water rising from the ground often introduces contaminating salts into the walls and plaster coats. This contamination will often result in a need for the plaster to be removed and replaced using specially formulated salt resistant plasters.
These defects are not always evident but when they are, a specialist inspection is always recommended.
Damp penetration usually refers to any water that enters a building and moved through the walls horizontally or from a higher to a lower level and is usually associated with external construction defects. Penetrating damp may move about within the building in various ways but is not rising damp.
Penetrating damp occurs as a result of problems with the fabric of the building that can allow water to leak into the walls or floors. Typical defects leading to penetrating damp are defective guttering or down pipes, faulty flashings, poor pointing, cracked rendering and built up external ground levels.
Penetrating damp is most common in older homes that have solid walls. A new build property with cavity walls offers more protection against driven rain. Penetrating damp can be tricky to pin-point, and may often require expert help.
The most common form of unwanted dampness in buildings is water from the air that forms as condensation.
The air in buildings can have a high level of relative humidity due to human activity (cooking, drying clothes, breathing and so on). When this water laden air comes into contact with cold surfaces such as windows and cold walls it can condense, causing water to be deposited. The point at which the water held in the air changes form vapour to liquid is known as the 'dew point'.
Condensation is often associated with poor heating and ventilation in buildings, but this simple view can be misleading. Condensation is chiefly a winter problem, the external air temperature is low and external walls and windows are cold. The usual sequence of events is as follows:
Walls in kitchens and bathrooms (where atmospheric moisture levels are usually highest), solid external walls, un-insulated solid floors and cold bridges such as concrete lintels set in cavity walls are commonly the areas in which condensation takes place.
Intermittent heating and cooling of the property can aggravate condensation problems, since it allows warm damp air to cool, reducing its capacity to hold water. Dew points are reduced allowing condensation to occur. When the air is reheated water is taken back into the air only to be deposited again when the air temperature drops again.
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