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There are numerous articles in both the press and some professional journals regarding rising damp and whether it is simply a myth. Indeed it has even been reported that the term ‘rising damp’ originated in official literature in the 1960’s whereas a simple search of authoritative publications shows the term to be used in the 1830’s onwards and is, in fact, recorded in the British Medical Association Journal of 1872.

This paper discusses what rising damp is and offers objective evidence for its existence.

Not simply a UK phenomenon, rising damp occurs anywhere that masonry is sufficiently permeable to take up water from the ground. Serious peer reviewed papers have appeared in scientific building and technical journals identifying that it is a problem in buildings throughout the world, especially including Belgium, Denmark, Italy and especially Australia, where it is referred to as ‘salt damp’.

Rising damp can be defined as water, which originates from the ground, rising up through masonry. The water rises via interconnecting pores within the wall by a process we refer to as ‘capillarity’ - in other words permeable masonry acts somewhat like a wick. However, the wick idea is not quite that simple. There are a number of factors that need to be present in order for the water to rise.

The pores within the wall must be sufficiently fine and interconnecting. Pores in masonry are reported to be as small as 0.001 mm in diameter, but around 0.01 mm is an average size. Pores of this latter size give a theoretical height of rise of 1.5 m. However, processes such as evaporation and pore continuity will in part control this.

Furthermore, think of the capillaries within the wall as a ‘suction’ agent, and similarly think of the ground as the same. If the suction of the wall is greater than the suction of the ground then water will rise if the capillaries are of a suitable size and sufficiently continuous. If, however, the suction of the ground is greater than the wall, then water will not rise, even if the pores within the wall continuous.

However, some have stated that rising damp is only caused by "mains water leaks", with the water soaking the ground. Basically, if the wall has sufficient suction water will rise from the ground whether there is a leak or not. Indeed, the most common source of water in the ground is rainwater where it clearly wets up the upper surfaces of the ground, ie, where the walls are in contact with the soil.

So in considering the factors described above it offers an explanation as to why not all walls without a damp proof course will have rising damp. Thus, for example, taking a section of Victorian wall and standing it in water to see if rising damp occurs, as some have done, cannot be used as a conclusive test for its existence or not.

Groundwater contains soluble materials, a proportion of which are soluble salts; these are usually present in lower parts per million and at this level they are of no significance. A proportion of the salts are soluble chlorides and nitrates, neither of which exist in building materials at any significant level, usually well less than 0.01%. So effectively we can consider the materials to be free from such salts

As the water rises from the ground into the wall these dissolved salts are carried in the rising water. As the water continues to rise and evaporate these salts are left behind, and over many years significant levels become deposited within the wall and finishes.

The majority of the salts are deposited towards the maximum height of rise of water where they form a distinct concentration known as the 'salt band'. Since these salts are, for all practical purposes, absent from building materials such as bricks, mortar, stone and plaster, it is their presence and distribution that holds the key to the diagnosis of rising damp.

Whilst there are a few occasions where such salts can arise from other sources, by far the most common occurrence of these salts in walls is water rising from the ground. Therefore in examining a wall suspected to be affected by long term rising damp, these salts will readily be found, but only up to the height of the rising damp - above the height of rise these salts will effectively be absent. So looking for the presence and distribution of these salts, especially in relation to the presence and distribution of water ingress, is essential for a definitive diagnosis. Condensation on the other hand, whether surface or interstitial, never introduces ground water salts into the wall and neither does rain penetration.

Condensation is often stated to be misdiagnosed as rising damp. However, in the UK there is a 'condensation season' and this is broadly between October and April. If there is dampness outside this period it is probably not condensation.

Furthermore, unlike rising damp, condensation is very frequently intermittent and if so may not remain sufficiently long enough to cause any visual problem. If condensation is long term then it is clearly readily evident.

It is unlikely therefore that condensation will be misdiagnosed as rising damp, especially during the warmer months of the year. Also consider that surface condensation literally penetrates permeable surfaces only a few millimetres if it is severe.

- salts and their distribution are the key to diagnosis of rising damp, together with whether water is still entering the wall.

- Moisture and salt 'profiling' a wall will readily identify the presence of rising damp as opposed to any other form of dampness.

Physical damp proof courses were introduced into ‘Regulations’ in the 1870s in relation to public health, although some properties were built with such dampness courses prior to this time. However, it did take a number of years before all properties were built including physical damp proof courses.

It is very unlikely, but not absolute, that a property with a physical damp proof course will have rising damp, unless the damp proof course becomes bridged – a problem which is usually readily identified - or seriously defective. Of the properties that do not have a damp proof course, some may have rising damp, others may not. Not having a damp proof course is not synonymous with having rising damp.

An article in a magazine produced by the BWPDA (the British Wood Preserving and Damp-proofing Association, now the Property Care Association) quoted a Building Research Establishment study, which reported that the Building Research Establishment had identified rising damp to a greater or lesser extent in 54 to 76% (dependent on whether the wall was a dividing or party wall) of the properties they investigated in Cardiff several years ago. These results together with other data suggest that rising damp is probably quite common in the United Kingdom. In Denmark, Belgium, Italy and Australia it is sufficiently common for Institutes to research and report on the problem, especially in relation to their historic buildings. However it appears likely that severe rising damp, sufficient to cause significant spoiling, staining, blowing of plaster and rot is far less common.

So does rising damp exist - a resounding yes. Can it be readily diagnosed – yes. It has very distinct features not present in other forms of dampness, but it may take laboratory facilities for a positive identification. Is rising damp myth - no, and certainly not in Europe and Australia.

Rising Damp - Technical Paper                                        
Rising Damp - Fact Sheet                                                

Review of Rising Damp - University of Portsmouth