April 16, 2019
In this post, Chartered Surveyor Stephen Boniface gives his advice on rising damp and how it is often misdiagnosed.
Many years ago I was asked to present a talk on dampness and I discovered that my talk was to be the first one after lunch. This is often known as ‘the graveyard slot’ because after lunch one feels rather tired and it is not unknown for delegates to drop off during the talk. I thought that it might be useful to wake them up with a controversial opening statement. I therefore declared “there is no such thing as rising damp”. I then went on to explain my views and in fact said much of what is to follow in this article. Nonetheless, I became known quite quickly as the building surveyor who does not believe in rising damp. To add to this a friend of mine in the professional world is Jeff Howell who once wrote a book called ‘The Rising Damp Myth’. Jeff and I once produced a training video discussing the issue. Apart from setting the record straight for my part in this article it is important that the issue of rising damp is understood. Bear in mind that most buildings I deal with are historic and, as discussed later, they are technically different to most modern buildings.
In the UK dampness is a major problem; brought about largely by our climate. It is perhaps the one thing that most property owners are most concerned about. This is quite understandable and is indeed a reasonable concern as dampness can cause a lot of damage to buildings.
However, there are many forms of dampness and of course many causes. The one that causes most concern for a purchaser or home owner is rising damp. Nonetheless, I would argue that rising damp is perhaps the most commonly misdiagnosed form of damp. And yet, in my experience rising damp is probably the rarest form of damp whilst condensation is probably the most common (although perhaps the least well understood).
Dampness means an excess amount of moisture. Note the use of the word ‘excess’ because most materials require a level of moisture otherwise they become desiccated. A certain amount of moisture in a material is not necessarily harmful. Indeed, for most building materials moisture becomes harmful when it has built up to such a level that it becomes manifest in some way, through smell or visually, or even causing physical damage. Of course, the assessment of damp should not rely purely on such tangible evidence, but without such evidence one must question the seriousness of the moisture level, if the only ‘evidence’ is a reading from a moisture meter.
There is of course the possibility that moisture is gradually building up and at one point in time there will be no physical evidence and yet a short while later the evidence could appear. Anyone assessing moisture in a building must be aware that moisture levels will change and a reading at any one time can be misleading. Here a proper understanding of other issues is necessary for a full and proper understanding of what moisture is doing within a building.
For many years now we have used a moisture meter to help detect moisture levels. Used carefully and intelligently this can be a useful diagnosis tool. Unfortunately, it is often misused, and its limitations are not fully considered by those using it.
There are many surveyors who, if a moisture meter gives a reading, recommend a further specialist investigation and report. Depending on the level of survey being undertaken this might be appropriate because for certain types of inspection it is not the surveyor’s role to diagnose the problem. However, there are times when one would expect the surveyor to undertake a full diagnosis and not refer the matter on for further investigation etc.
Indeed, this is where the misdiagnosis (or perhaps unwillingness to diagnose) often arises and causes problems. Surveyors obtain a reading and then request a specialist report with that report then prepared by a company whose primary function is to undertake specialist treatments. Although that company’s surveyors may be trained to diagnose damp problems, they are first and foremost sales people. They have a vested interest in finding a damp problem that they can then treat; for some working on a commission basis it is the difference between earning a decent wage or not. This then leads to work that, in my opinion, is often unnecessary and therefore a waste of the clients’ money.
The problem is compounded by the fact that surveyors and other professionals have to undergo something called ‘Continuing Professional Development’. They have to demonstrate to their professional bodies that they have undertaken studies (perhaps attended courses) covered a certain number of hours of CPD each year. A number of specialist treatment companies offer free CPD to surveying companies, etc. On the face of it this may seem very helpful but of course the companies are there to sell a product. Many surveyors rely on such CPD for their dampness training and it is therefore no wonder that these surveyors automatically think that if they obtain a reading on their meters then they should refer the matter on to one of these treatment companies.
To compound the problem further many mortgage valuers are required to use certain phrases when completing valuation reports. If they find evidence of, or suspect, a damp problem they are often required to refer the matter for specialist investigation. The mortgage companies usually require that such investigations be undertaken by a company belonging to the Property Care Association (PCA). Most (not all) of PCA’s members are treatment companies.
There are many good surveyors and other professionals out there who are not members of PCA and yet are perfectly competent at properly assessing dampness and do not have a vested interest in any specialist treatment. Of course, some members of PCA do offer impartial advice as not all are reliant on selling a particular treatment. You may also find that some of the treatment companies might be persuaded to provide impartial advice if paid to do so.
I have so far discussed the problem of why dampness, specifically rising damp, is often misdiagnosed; through ignorance and vested interests in a certain approach. So, let me now consider the matter of rising damp.
Many materials we construct buildings with are to some extent porous and/or permeable, thus allowing moisture to enter the material. Such materials (brick, stone, mortar, etc.,) will therefore contain moisture. The argument for rising damp is that these materials absorb moisture from the ground and that it then gradually builds up and continues to rise up the wall until it becomes a problem. It follows that the logical treatment for this is to insert a horizontal barrier, hence the need for chemical treatment as a retrospective remedial measure. This assumes that once a material has absorbed moisture it will not release it and therefore the level of moisture gradually increases to eventually become a damp problem.
However, with most building materials they will not only absorb a degree of moisture but will also release it. Unless the material is continuously wet then the level of moisture will ebb and flow, as the material sometimes wets up and then for periods will dry out as the moisture is released. It follows that the base of a wall might be damp on occasions but will dry again and the moisture never actually builds up sufficiently to ‘rise’ up the wall.
Another argument for rising damp is that there is a form of pressure behind the moisture thus keeping it in the wall and forcing it up the wall. However, one only has to look at many moated historic buildings to realise that water will only rise a certain level before it evaporates from the surfaces. If you look at any flooded area the tidemark of the water is not often more than a few centimetres, perhaps 300mm or thereabouts, above the level of the water. Our ancestors knew what they were doing when they constructed houses whereby the ground floor was raised up and you walked up steps into it. If the ground floor is high enough above the zone likely to become damp then there is in fact no need for a damp-proof course, because the damp should never reach high enough to cause a problem.
If a wall has no cladding or other finish to it the moisture can freely evaporate from the wall material. The moisture will accumulate at the base of the wall and will appear to rise as it accumulates. However, if it can evaporate from those surfaces there will come a point where the rate of evaporation from the wall is greater than the rate of uptake. This zone creates what we often call a tidemark on the wall. Under normal circumstances in a conventional 9” thick wall this damp zone is usually only in the bottom couple of courses – perhaps 6-inches (150 mm). This is why, in the late 19th century, the Victorians required houses to be built with a physical damp proof course two courses of brickwork above ground level. They knew that this was approximately where dampness would naturally evaporate out; the damp proof course was there as a secondary barrier to ensure that if moisture did not evaporate quick enough and tried to rise slightly higher it would not cause an internal problem. Therefore, it seems that, from observation logic and understanding of buildings, one can see that true rising damp will only usually occur in the bottom couple of courses of brickwork.
Of course, there are situations that affect the risk of damp being a problem in the first instance. A building constructed in a valley on impermeable soils could find itself sitting in a moist situation for much of the time. In these situations, it is far more likely that the walls will never fully dry out at the base and there is a greater risk that moisture could find a way of rising further up the wall. However, a building constructed on a very permeable subsoil or on the top of a hill will very rarely have water sitting under it for any great length of time because the ground water will naturally flow away from the building meaning that the walls are not generally sitting in damp soil and are unlikely to become excessively damp anyway.
Where one has a damp wall, one must first consider whether the wall is likely to be in a damp location, be sitting in a wet soil, or in some way exposed to an excessive amount of ground moisture that could then be contained within the base of the wall. Over the years I have come across such situations but have found that careful installation of ground drainage and external channels can divert ground water such that the building itself does not remain excessively damp.
A common problem is where walls have been coated over the years with render or perhaps other impermeable finishes externally and sometimes by impermeable finishes internally. Another frequent problem is that the ground level externally has been increased such that the ground against the building is high in relation to internal ground floors or bridging the damp proof course. Where a building has suspended timber floors and there is a ventilated void underneath, we sometimes find that this has had the ventilation blocked off as such that there is no airflow.
All of these scenarios can give rise to moisture being contained within the base of the wall and not being able to escape. In such situations there is a possibility that the dampness will eventually rise, or appear to rise, up the wall. This is simply because the moisture has become trapped and cannot escape.
In such situations the remedies are usually fairly obvious. Removing impermeable finishes to allow the wall to release the moisture can often go a long way to resolving a damp problem. Opening up vents to ventilate voids can also assist drying out sub-floor areas. Most importantly, lowering ground levels against the building can assist because then there is no longer the problem of moisture penetrating laterally through the wall. I often find that by dealing with such matters the problem of dampness can be resolved without the need for specialist treatments.
It must also be remembered that there may be other reasons why the base of the wall has become damp. Some years ago friends of mine were trying to sell their house. They were both building surveyors and both involved with historic buildings and therefore understood these issues. Their purchasers mortgage valuer undertook the usual tests and found an area of damp and declared that there needed to be a specialist report undertaken. That report concluded that there was a rising damp problem and the wall needed to be treated. My friends refused to accept this because there was no internal visible evidence of a problem and they suspected that such treatment could cause problems. They quickly discovered why this area of wall gave a high reading – there had been a leaking gutter joint for some time that they had not realised was causing such a problem. The water from this had gradually dripped onto the ground and splashed into the base of the wall. This created a localised problem of dampness in the wall. Internally it meant that a moisture meter gave a reading to a certain area and this caused the specialist company to decide that the appropriate remedy was chemical treatment. In fact all that was needed was repair of the gutter and allowing the wall to dry out. This they did and then successfully sold the property without the need for any treatment.
Modern buildings are constructed in a way whereby the design is intended to keep out moisture. Modern buildings tend to incorporate physical barriers and have materials that prevent moisture getting into the building. This is all very good until that system fails and then when moisture enters it can often be quite difficult to find the point of entry and where one needs to repair. In some situations, there may be a need for some form of specialist intervention, especially in buildings designed to keep moisture out.
However, for hundreds of years buildings were constructed and functioned differently. With older buildings (often taken to be those built before about the 1920s), the materials were permeable, and the buildings manage moisture rather than exclude it. Therefore, a certain amount of moisture would be absorbed into the building fabric but this would then evaporate away again without causing any long-term problems. If we impose modern technology on older buildings, there is a chance that we create a barrier that was never intended to be present. This can sometimes result in the moisture finding a way around the barrier or dispersing in areas where previously it might not have been present. In other words, inserting a barrier into an older building can sometimes force the moisture problem elsewhere rather than resolving it.
Of course, if it were possible to introduce a complete infallible barrier under every part of an old building this would resolve any problem of damp from the ground into the base of the building. However, I have yet to come across any retrospectively inserted system that can be inserted under all parts and is indeed 100% infallible. Even if such were available the cost and disruption would probably be inhibitive for most buildings.
In reaching a conclusion to this article I recap as follows.
Has the ground level increased against the wall?
Have sub-floor vents been blocked up?
Has render or some other impermeable finish been applied externally or internally?
Are there leaks in or about the area?
Of course, there are situations where the analysis of a damp problem will be more complex. It may be necessary to employ techniques such as taking core samples from the wall to assess the dampness.
There again there may be situations where the cause of the damp cannot be resolved. For example, where there are high ground levels, but it may not be possible to lower the ground against the wall.
A good building surveyor will be able to properly diagnose a damp problem looking at it holistically and taking all matters into account to devise a remedy that is appropriate for that specific building in those given circumstances.
Modern technology provides us with new tools to assist in the diagnosis of damp – thermal imaging for example; a useful tool, but perhaps dangerous in the wrong hands!
I conclude by saying that rising damp may exist in some situations, but it is rare. Often the cause of what seems to be rising damp can be found to be something that has happened to that building – what has been done to bring about a change to the building? I am not saying that there will never be a need for specialist intervention but in my experience, it is extremely rare.
If you have what is thought to be rising damp, then seek advice from a competent independent surveyor who will take a holistic look at the problem and devise a bespoke remedy. It is not free or cheap, but it is independent and provides a remedy specifically for your building and situation. At whitworth we can provide such a service; call us today on 01284 760421.
Towards the beginning of this piece I mentioned condensation, and this will be the subject of a separate article.
About the author
Stephen Boniface is a Chartered Surveyor at whitworth. Stephen has extensive experience in historic buildings and conservation work, and on a daily basis carries out a variety of work from surveys to expert witness.