Have I got Rising Damp?


Have I got Rising Damp?

Is a question we get a lot of calls about!

To the inexperienced builder, DIY person or homeowner, when looking at damp at the base of an external wall, many jump to the conclusion they are faced with rising damp. On the flip side, some will say rising damp is a myth.

To address that second point; a bit like religion, we take the view that everybody is entitled to an opionion or belief. If yours is the opinion that damp from the ground does not exist then we will respect that. Equally, as humble observers, we read and come across too much information that supports damp in the ground travels up through floors and walls for building materials being used that promote capillary rise from the ground or, for there not being a damp barrier to prevent this otherwise known as a damp proof course, (DPC).

Our supporting information is taken from the fact that since mid Victorian times and due to the introduction of failed sewers and mains water supplies, the term ‘rising damp’ was invented and dampproof coursing introduced. Leaking pipes are a much more serious source of persistent water than the water table and the problems seem to have been exacerbated when cement renders were  introduced as a remedial or decorative measure (these prevent evaporation and so drive moisture further up the wall).

Often the render will have been applied in response to a moisture problem and thus, have made the situation worse rather than better. Impermeable finishes may also make it difficult to locate the true source of water.

By the late 1870s damp-proof coursing had been incorporated into English building legislation.

However, the original cause of a damp problem is not always understood and ‘rising damp’ has become a catch phrase for all moisture problems in walls, even when the water is percolating down from above!

So, for building regulations stating we MUST use a damp proof course and for this being the case since the 1870’s we have one other piece of information to offer which we take from the English Heritage body and from their ‘Building Enviromnet’ document in which they state;

“If a sample of permeable material is exposed to a continuous source of moisture at its base, water will rise up to the point where the rate of uptake equals the rate of evaporation”.

This is labelled as capillary rise in their document which we know more commonly as; rising damp.

The key point is about identifying correctly what the source of moisture at the base of a wall is as, if correctly identified and ‘fixed’ the ground will dry out and the base of the wall will dry down. This for instance, could be faulty guttering, cracked drains, raised ground levels or a personal pet hate, rendering with porous materials completely down to the ground! All of these points could be the cause of internal damp at the base of a wall and have absolutely nothing to do with a failure or lack of a damp proof course.

One of the most common causes we encounter for internal damp mistaken for ‘rising damp’ is what is otherwise called; Bridging damp. The reference to bridging is simply where a medium has come about whereby a bridge has formed to allow moisture on the outside of a property to travel across to the inside. Again, nothing to do with rising damp and more often than not, once identified you simply remove the cause for the bridge and the internal side will dry down naturally.

Typical causes for a bridge are:

  1. Raised external ground levels for laying new block paved drives, commonly on top of a tarmac drive that the new top level is now close to, equal with or even above the damp proof course. The same occurs for laying more and more top soil on top of flower beds that are built up against external walls. In the instance of a cavity wall, the bridge will be formed by debris at the base of the cavity wall which is left over from when the property was constructed. Building sand, sections of brick, mortar, even bits of scaffold! In the case of solid walls, the mortar and brick will be porous and draw moisture to the inside.
  2. Corroding wall ties can act as both a damp bridge and cold bridge.
  3. Cavity insulation material can act as a bridge.

Hopefully we have described this well enough as the solution often means work can be carried out from the outside to resolve the problem. The key is to determine the internal plaster is still sound and if it is, allow a sufficient drying period before redecorating. Typically, you should allow one month per inch the thickness of a wall as the drying period. This is reduced in summer months or accelerated with good ventilation and ambient background heating.

We highly recommend that property owners engage a suitably experienced or qualified remedial contractor or surveyor to diagnose the reason for damp in a bulding.

So this is one explanation of why damp can appear or assumed to be ‘rising’ damp when in fact its not however, for our part, rising damp is a phenomenon and when correctly identified can be succesfully treated with a chemical injection damp proof course with products approved and tested for their ability to do so.


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