I was talking to a man the other day, and he told me how he had narrowly ‘escaped’ buying a house with rising dampness, which was so bad, it had reached as far as the rafters! He was deadly serious as he told this tale, and I think he believed every word of it.

Once back inside the safety of my car, admiring the striking colours of the parking ticket on the windscreen, I got to thinking about what he had said, and how he had said it.

I pondered, not for the first time, that rising damp is up there with the best of the urban myths, and the tales we hear about it finish up in the compartment of one’s mind labelled, ‘Phew, glad that happened to someone else’.  Somewhat amusing, but at the same time slightly menacing.

Not everyone takes it that seriously though, and balancing the tales of woe from the ‘Ain’t it wet and awful camp’, are the massed, and growing, ranks of the ‘Rising Dampness Denial’ squad, with Brigadier Jeff as their Commander in Chief. A task in which he is ably abetted by Konrad (never knowingly understood) Fischer, and although I can’t agree with either of them, I think their opinions deserve a link, particularly Konrad, who puts so much energy into his work.

But it seems that Jeff et al can’t have seen the photograph below (courtesy of Paul Carter at PC Preservations, and they certainly haven’t been with me when I’m considering its implications for a concerned house owner.

Yes, it does exist; but as with lots of things in life, its existence isn’t really the question.  It’s its effects that are far more relevant to you and yours. 

As with other articles on this site, I don’t intend to go into hugely technical detail, as once again, others have already done that and you can read such articles all over the Internet.  However, as a beginner’s guide, here goes:

The makeup of brickwork, stonework or other masonry products is such that they have very fine tubes within them, called capillaries, and although these are more usually associated with the circulation system in our bodies, they also exist in other, inert substances.

These capillaries have the ability to draw moisture up in to them, and you can get an insight into this process here. As a rule of thumb: the finer the tube, the higher the moisture will rise.

Thus, if we place an absorbent material, e.g. a common brick or piece of sandstone, onto a surface containing free water, that water will rise into it.

Just how far it rises depends on several things: the pore structure of the material; gravity; the amount of water available in the first place; and the rate of evaporation that takes place from the material’s surface. In addition, if it’s a house wall we’re talking about, the ratio of the wall’s thickness to its surface area also plays a part.  More on this later.

With the exception of gravity, which is pretty constant where I live, all of the other factors are variable: some bricks, such as engineering bricks, have a dense structure, and the pore availability is limited - they could be considered to be almost impermeable.  Other bricks, like ordinary house bricks, have an open pore structure, with more capillaries; and other things being equal, this type of brick will absorb water more easily.

The mortar beds that separate the bricks or stones will also have varying characteristics; and given the right circumstances, these joints can ‘short circuit’ the bricks, no matter how dense and impermeable they are.  That’s why in some types of house, which use engineering bricks as a damp proofing course (dpc), rising dampness can appear many years after they were first built.  The bricks do their job quite well and they don’t become damp; but the mortar surrounding them does.

Naturally enough, if the ground that the wall is standing on is bone dry, there won’t be any moisture available to rise in the first place; but if a wall is standing on ground that’s wet, because of a high water table for instance, this obviously isn’t so.  It should also be recognised that the availability of moisture in the ground may rise and fall with the weather conditions or seasons.

As the water rises in our wall, some of it will naturally find its way to the outer face of the brickwork/stonework, where it will come into contact with the atmosphere.  At that junction, evaporation will take place, although the degree to which this will occur is also a variable factor.

If the wall is in an area of high relative humidity, not much in the way of evaporation will take place and the masonry will stay damp; if other conditions are favourable, this will allow it to rise higher than it otherwise would.  However, if it’s buffeted by warm, dry winds, it will lose its moisture very quickly.  And as the surface moisture is removed, and the source of that moisture is relatively constant, the height to which it will rise is reduced. After all, if it’s all being evaporated into the atmosphere from the first inch or so of brickwork, there isn’t going to be any left to climb up inside the wall.

Finally, the ratio of the wall’s thickness to its surface area is important.  The thicker the wall, the lower this ratio is (or higher depending on which way you look at it).  Thus if you have a wall that’s three feet thick at its base, it will have more moisture bearing capillaries than a similar one that’s only four inches thick; but the surface area available for evaporation is usually almost the same in both structures, and the moisture in the thicker version can, and will, rise higher.

It’s this ‘variability’ in materials and circumstances that defines whether any rising dampness is an actual problem, or merely an interesting phenomenon. Sure, if the circumstances are right, it will rise in the wall to a fair height, usually up to 900mm or so, although this should not be considered a maximum. However, in most circumstances, evaporation takes its toll on the rising moisture before it becomes a significant problem for your walls; and soaking the roofing timbers is usually well beyond its capabilities!

So, back to the ‘does it or doesn’t it exist’ argument.  Well, in my experience, and depending on the individual circumstances, moisture can and does rise into the base of walls from the earth beneath; and that, at least in my opinion, constitutes ‘Rising Damp’.

That this can happen has been recognised in the building establishment for many, many years.  In fact, in 1877/8, because of general disquiet at the condition of new housing, particularly terraced housing in large cities, such as Manchester and Leeds, the ‘Model Building Bye Laws’ (App A, p.86) recommended the inclusion of damp proofing courses in all new properties. These were to be made of slate, lead, asphalt or other durable materials impervious to water. You don’t often see lead ones but the other two are quite common in older houses.

Unfortunately, these recommendations were not generally adopted by all builders until the turn of the century, and even then, if the builder didn’t feel like including one it’s highly unlikely that a local Building Control Officer (BCO) would have saddled up his horse and visited a site to check up. Fortunately, these days the BCO’s have eyes like the proverbial hawks and think nothing of firing up the Mondeo to take a look at life outside the Town Hall.

When dpc’s did become generally adopted, they were usually in the form of a layer of blue-slate; engineering brick; or, towards the end of Edwardian times, rolls of felt that had been soaked in bitumen. These were inserted between two courses of brick, or stonework, just above ground level.  And even though all of these systems get a little ‘tired’ over the years, they don’t usually fail catastrophically. At least, not without having undergone some form of physical disturbance, such as might be found after subsidence etc.

And that leaves us with a huge amount of housing stock – built before the Bye Laws – that don’t have the ‘benefit’ of a damp proofing course, which begs the question: “why aren’t they all wet through then?”.  Because I can assure you, the majority of them aren’t.

And this is because of two things: a fortuitous combination of the circumstances mentioned above; and the materials that older houses were built with.

Considerate builders in days gone by, although perhaps not quite as sensitive to criticism as those of today, nevertheless did not relish their clients complaining that their walls were damp.  Fortunately for them, one of the materials they used to build walls (putting one on two, and two on one, as a brickie I once knew described the building of walls) went a good way to helping with the problem: and that material was lime mortar.

When lime mortar is used to bond the masonry together, it effectively surrounds it with a material that easily allows the evaporation of moisture, and in the vast majority of walls, this ensured that any ‘rising dampness’ was despatched into the atmosphere almost as soon as it entered the lower courses of the wall.  Naturally, this relied upon good ventilation, but in most cases, this was readily available.

The result of this process of evaporation was that moisture entering the masonry was balanced by that leaving it, and unless conditions were particularly difficult, only the very base of the walls was in any form of jeopardy, and even that was limited.

In addition, the plaster on the internal walls was invariably lime-based too, and this also allowed evaporation without suffering damage itself.  Thus, although the lower reaches of the walls may have had a slightly higher moisture content than those at the upper levels, this soon settled down to become the wall’s natural condition.  It rose and fell slightly as the seasons unwound, but it didn’t do any harm to the internal finishes or skirting boards.

Because nothing was noticeable, rising dampness was never a significant issue in the majority of houses, and it remained that way until the advent of modern improvements to the housing stock, particularly double-glazing – and the increased use of moisture meters!

There’s mention elsewhere on this site of the rise and rise of these meters; the reasons behind their almost ubiquitous use; and the dangers they pose for the unwary property owner, especially in the hands of the unscrupulous damp proofing salesman.  Without labouring the point, moisture meters are extremely sensitive instruments; and even when used correctly, they can be misleading.

Also, in the majority of instances, they are used as the sole arbiter of whether a property needs treatment for rising dampness.  That they cannot tell you how much moisture there is in your walls is immaterial. According to the damp proofing salesman, if the meter goes red, or emits a steady peep-peep-peep, then you need an injection damp proofing treatment, or similar. Meter says ‘Yes’. End of story.  At least that’s the line taken by many of those who sell these systems.

However, what seems to me more to the point is that if the walls in your house have had a slightly higher level of moisture at their base for a hundred years or more, and that moisture has not caused any damage to anything else, it cannot be right to spend hundreds, or even thousands of pounds trying to remove it, regardless of the blandishments of salesmen or the concerns of valuation surveyors.

So in conclusion: yes, your house may have a degree of ‘rising damp’: but seriously, does that matter? If the only way you’d know about it would be to go out and buy a moisture meter then I think you’d be right to leave things as they are, especially if any ‘treatment’ involved the destruction of original lime plaster that had been there for decades.

If damage is being caused (see photo), then only a fool would ignore it and I’m certainly not going to go down that path: I left my rose tinted spectacles at home years ago. But at the same time, unless someone can satisfactorily explain to me the reasoning behind installing - at great cost - a system that seeks to hide something that can’t be seen in the first place, and which isn’t causing any problems other than for draining the batteries in a sensitive electronic meter, I shall carry on telling people to save their money for better use.

That doesn’t put me in the same boat as the ‘Deny it’s happening Brigade’ but it does seem a bit more logical.