Damp in buildings
Excess water/moisture in all its forms (vapour, liquid, and flooding) is still the most common problem in housing. Damp in buildings may be apparent from:
- Damp patches.
- Mould growth, which is a cause of respiratory allergies.
- Mildew, salts, staining and 'tide marks'.
- Damage to surface finishes, such as blistering paint and bulging plaster.
- Corrosion and decay of the building fabric.
- Slip hazards.
- Frost damage.
- Poor performance of insulation.
- Damage to equipment, or electrical failure.
Successful treatment can only be achieved if the type of dampness is correctly diagnosed. The complexity of existing buildings means that dampness is very often misdiagnosed, leading to future damp problems, cost and disruption to the occupants.
The most common causes of persistent damp in buildings are:
Condensation occurs when moist air cools below its dew point, and water condenses. This can occur as surface condensation, but can also occur within the fabric of a building itself, as interstitial condensation.
Rising damp is caused by incorrect placing of, faults to, or the absence of a damp-proof course, and is generally only apparent up to 1m above ground level because of the limits of capillary action to draw moisture up through porous elements of the building structure. Rising damp can be exacerbated by alterations to ground levels, flooding, leaks and so on.
See Rising damp for more information.
See Penetrating damp for more information.
There are four established methods for diagnosing damp.
Manual viewing is the least costly, but potentially least reliable method of diagnosis.
 Moisture meters
Moisture meters can be used to confirm the observed diagnosis. In skilled hands with regular site calibration moisture meters can be a good starting point, however, depending on the complexity of the building, the materials used, its present condition and maintenance history, moisture meters can lead to misdiagnosis.
 Laboratory techniques
Drilled samples and moisture contents can be subjected to techniques such as a carbide meter, oven drying and soluble salt analysis. However, these are always helpful but, like an MOT on a car, are only valid on the day they are taken.
 Temperature and humidity measurement
Recording the relative humidity and temperatures in a series of rooms and outside using half hourly sampling is the most effective way of diagnosing damp. The 'data' from the surveys would help to inform the project manager on the time scale, for not only the current condition of the building, but how long it could take to dry down.
 Related articles on Designing Buildings Wiki
- Basement waterproofing.
- Building fabric.
- Cavity tray.
- Cold bridge.
- Damp-proof course.
- Damp proof membrane.
- Defects in brickwork
- Defects in stonework.
- Dew point.
- Dry rot fungus.
- Interstitial condensation.
- Penetrating damp.
- Rising damp.
- Rising damp in walls - diagnosis and treatment (DG 245).
- Wall insulation and moisture risk.
- Wall tie failure.
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