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| Question | Answer |
| What is rising damp? | Rising damp is moisture present in your walls as a result of water in the ground underneath or next to your walls rising up through the fabric of the wall. Water travels upwards through the wall as a result of capillary action (where water is sucked through a small opening such as a tube or hole) through the tiny holes in the brick or stone. The water stops rising at a height where gravity counteracts the upwards force of the capillary action. This ‘rising damp’ usually reaches a maximum height of 1.2m. Below ground moisture sources include : - 'free' water in the subsoil (high water table) - building up from drain or pipe leaks - a water main breach |
| What are the causes of rising damp? | Rising damp problems often occur as a result of not having a Damp Proof Course installed or having a Damp Proof Course that is faulty due to age or inadequate installation. You may be experiencing rising damp even if your Damp Proof Course is functioning well. - It may be that there is an area of ground next to your external wall that is higher than your DPC, or there is an outside structure (such as steps) which is attached above the DPC, allowing water to travel up through this and cross to the wall over the DPC. - A cavity wall may also have debris inside of it, whether it is leftover building materials or something else. If this debris reaches above the DPC's then this can create another bridge for moisture to travel from the ground over the DPC and up your wall as rising damp. |
| What are the characteristics / factors associated with rising damp? | Typical signs of rising damp rather than other damp problems are a ‘tide line’ of yellowish or brownish staining or blown plaster in the lower area of a wall above the skirting board. Skirting boards or flooring may also be damp or rotting. You may see white, fluffy deposits on the walls – these are ‘salts’ which the damp has washed out of your bricks and into your plaster. Black spots of mould may also appear on on the damp areas of your wall. |
| What is penetrative damp? | Penetrating dampness refers to any moisture sourced from outside the habitable space. This includes: •precipitation (rain, snow, sleet, hail and fog); •moisture from external plumbing leaks (soil, waste, rainwater and so on); •any moisture entering a wall above the ground, but below the dpc level (i.e. a dpc controls moisture sourced from below the ground and moisture sourced just above the ground - penetrating damp). |
| What are the causes of penetrative damp? | Penetrating dampness occurs through roofs, chimneys, parapet walls and walls above ground level. Various physical mechanisms enable moisture to enter the fabric: •gravity pulls rain vertically in through weak points in the roof or other horizontal surfaces; •lateral winds force moisture through cracks and gaps in walls; •surface tension enables moisture to penetrate under horizontal soffits and cills where there is no effective drip; •a higher external pressure can cause water to penetrate through gaps in the envelope. |
| What are the characteristics / factors associated with penetrative damp? | •Needs a link from outside to inside, but does not always appear opposite the source. •Needs time to percolate into the building. •Carries soluble contaminates like sulphates and carbonates. •Can be mistaken for rising damp if the cause is low down the wall |
| What is condensation? | Condensation is the moisture caused by everyday living and occurs when warm moist air comes into contact with cooler air, or a cold surface, which is at a lower temperature. |
| Explain the different types of condensation? | Surface condensation is probably the most common type of condensation found in dwellings. This is usually observed as water (distilled) droplets streaming down a cold windowpane or on the surface of bathroom tiling. It can also moisten more porous surfaces, typically at cold room corners, where mould colonies may then grow in a characteristic crescent-shaped pattern at the skirting or ceiling junction. Interstitial condensation occurs within or between the layers of the building envelope, where the dew point exists at depth within a building element, component or material (for example, where water vapour has entered the roof void and condensation has occurred to the cold underside of flat roof decking). |
| What are the causes of condensation? | Temperature levels, ventilation rates, and the amount of moisture available all play a role in condensation. Remedy principles : - heat the property to warm up cold surfaces - improve ventilation to expel moisture laden air - insulation can decrease surface condensation but risk of interstitial condensation remains |
| What are the characteristics / factors associated with condensation? | •Causes mould marks in still areas like cupboards and behind furniture placed against walls. •Needs cold(er) surfaces to form water. •Does not contain contaminates. •Likes cold homes where lots of moisture is created. •Can form inside walls and roofs |
| What methods / techniques can be used to determine the source of dampness? | Rising damp Sometimes it is possible to confirm that moisture has come from the ground by carrying out a chemical analysis. Salts testing, for example, may help you to confirm that salts found in walls or their finishes above ground could only have been derived from sources below ground. Penetrative damp Internal damage and staining to finishes are usually easily linked to the area of external penetration. But where damp is penetrating a cavity wall or flat roof construction, the link between internal symptoms and external building faults may be less obvious (figures 1 and 2). Infrared thermography can be useful here, because this technique will identify surface temperatures that can be linked to symptoms of dampness. Although it is not common practice, surveyors should consider excavating trial holes in a dampness investigation: •to confirm the existence of a dpc that has been concealed by raised ground levels externally; •to verify the construction of walls below ground; and •to establish the height of the water table |
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