Environmental Dampness Control



Environmental dampness control & moisture vapour movement (moisture control) with the use of damp-proof or hydrophobic materials creating a comparatively less permeable moisture barrier is not essentially a cost effective option in controlling damp in walls and solid floors in houses.  It can sometimes be counter-productive. The reason being is that the use of relatively impermeable materials will restrict moisture movement and evaporation and consequently drying out; resulting in the moisture being sealed into damp materials for many years and causing serious timber decay problems in the built environment, such as wet & dry rot. The moisture may also be prevented from dispersing from permeable materials, resulting in a build-up of moisture or even damper conditions in localised areas or give rise to the movement of moisture into previously dry structures where evaporation from previously unaffected surfaces would cause salt efflorescent to appear. The first objective of any environmental dampness control strategy must be to cut off water ingress supplies to damp problem. If for example, a faulty down pipe has been identified as the major cause of the elevated moisture levels in an area of a building then this should be corrected as soon as possible. There is no point in spending time reviewing and evaluating various damp-proofing repairs & estimates for rising damp treatment whilst leaving the cause of the problem unattended to. So the cause of  the damp problem should be ‘cured’ as soon as possible after identification.

A common example showing the effect of inserting a damp-proof material into a structure is the sudden appearance of ‘rising damp’ in walls after the laying of a new concrete floor incorporating a damp-proof membrane. (Usually when a suspended timber floor has been replaced with solid or when a breathable stone slab floor is lifted and re-laid with a damp-proof membrane below). The original substrate below the timber floor or breathable solid floor would have allowed moisture to evaporate off the large surface without affecting the internal walls and finishes. However with the introduction of an impermeable membrane, the elevated moisture levels accumulates beneath and is forced out to the sides and into the base of the walls. This will cause damp and timber decay problems to occur in a house unless suitable ventilation is provided at the floor/wall junction. These damp symptoms are often used by some damp-proofing and timber treatment contractors to justify the injection of a damp-proof course (moisture-barrier) and the removal and replacement of specialist damp-proof plaster. The most cost effective damp control alternative would be to allow the original floor structure to continue to ‘breathe’. This would occur with a suspended timber floor or by providing a ventilated skirting detail at the floor/wall junction in such a way as to allow the residual moisture to evaporate.

If it is decided that a moisture barrier is essential at the base of the walls, then the most dependable technique would be to introduce a physical barrier rather than a chemical one. This method would involve the ‘cutting-in’ of a layer of damp-proof material to form a continuous barrier with the damp-proof membrane under the floor. As the wall above this barrier will remain damp for some time, it is essential that susceptible materials (i.e. skirting boards) above as well as below the barrier are isolated from the base of the wall with a damp proof membrane or ventilation air gap

A damp-proof barrier is always susceptible to localised failure resulting in concentrated moisture and damp at these points. (This is a general characteristic of all impermeable materials which are generally found to fail at some point). Because of this, traditional building techniques rely upon the use of permeable materials and ventilation systems to disperse moisture and prevent it coming into contact with susceptible materials and internal surfaces.

‘Chemical damp-proofing’ may provide a useful barrier in controlling rising dampness in the short to medium term, however, any gaps which are left, or which appear over time as the building material weakens, may lead to damp ingress and possible timber decay to walls & floors of houses.


Ground drainage is the most cost-effective environmental dampess control method of controlling rising dampness & timber decay in old buildings, including that which results in damp masonry at the lower part of the wall. Reducing moisture sources and providing adequate passive moisture sinks to disperse any penetrative moisture will make the system fail-safe.

This should start with the provision of sufficient ground drainage around the building, thus minimising water penetration and controlling rising damp to the foundations, and the re-routing of surface drainage away from the base of the walls. The ‘French drain’ system has become fashionable to help with this process. This consists of a channel dug along the base of the wall and filled with shingle. However, these often become blocked with debris and soil which prevents proper moisture drainage and evaporation from the foot of the wall. A more traditional method used in the UK, is to provide a ventilated and drained ‘dry area’ around the base of the wall, which are generally enclosed with flag stone slabs thus preventing debris accumulating in the drained dry area and therefore reducing maintenance. When providing the latter system, the flag stones MUST be a minimum of 150mm below the damp-proof course level.                                                                                                                                                              RESIDUAL DAMPNESS ENTRAPPED IN BUILDINGS 

The use of dense finishes, such as sand/cement renders, around the base of external elevation of walls is a regular cause of damp problems. These finished prevent moisture evaporating from the base of the wall; instead the moisture is forced into the internal walls surface, where evaporation takes place, and leads to decorative spoiling and timber decay.

As with all impermeable materials they will eventually break down with age, allowing water seepage into the base of the walls, but preventing evaporation and drying of the wall to take place. Using a more traditional ‘breathable’ renovating lime mortar and the correct finish of external renders projecting water away from the base of the wall, thus preventing the bridging of any existing damp-proof course system, would be the desired solutions.

Providing that a Cavity wall construction is through ventilated, it may provide a way of dispersing moisture and prevent it penetrating through onto the internal surface of a building. If debris, or the ill-advised injection of insulation foams, fills the cavity, bridging of the existing damp-proof course may occur allowing water to penetrate through to the interior surface and lead to the spoiling of decorative surfaces or timber decay. Sometimes, the most cost effective solution would be to re-establish a through-ventilated cavity.

In general, the breakdown of an existing damp-proof course usually results from the bridging by incorrect repairs and alterations, raised ground levels, localised damage due to structural movement or poor building maintenance.

If a damp-proof course is an original design (i.e. physical damp proof course) to control moisture movement in the structure, it may be necessary to carry out local repairs. Ideally this is best done by ‘cutting in’ a new layer of damp-proof material locally, however this is the more time consuming, disruptive and therefore the more expensive method.


Conventionally, buildings which are built on damp or potentially damp sites generally include sub-floor through ventilation cavities, basements / cellars. These areas act as sumps to allow the evaporation and dispersal of moisture ingress from the structure before it extends to occupied areas or susceptible decorative finishes.

If the sub floor ventilation of basements, cellars or sub-floor cavities is restricted, moisture will build up and penetrate susceptible structures increasing the risk of dampness and other sub floor ventilation problems, such as timber decay to joists, & wood boring beetle infestations. This can arise for example by soil/plants or raised ground levels blocking up the sub-floor air bricks or by the application of waterproofing materials. The solution to these problems would be to use environmental dampness control methods which will  increase the ventilation still further, not to start applying further waterproofing materials to the substrate.

As mentioned earlier, the re-in-statement of a through-ventilated suspended timber floor is generally preferable to the replacement with a solid concrete floor. The requirement for continual dispersal of dampness should not impede the use of basements and cellars as occupied areas, however the walls should be kept well ventilated and not sealed.

This can be achieved by using a through-ventilated dry lining system rather than an impermeable finish or a rendered tanking system, which would force moisture into adjacent structures to the side or above.

Traditionally, ‘dry lining’ has been applied by using timber paneling, isolated from the masonry with timber battens or the use of lath and plaster. In such cases, the void behind must be ventilated at the top and bottom thus allowing through-ventilation to occur and aid in the evaporation of moisture. Failure to supply this ventilation will lead to the build-up of moisture causing damp and timber decay to occur. This commonly happens when insulation material or building debris is allowed to block the cavity behind lath and plaster, or when numerous layers of paint accumulate over timber paneling. By using timber paneling to dado level, this can provide an attractive and cost-effective answer to problems of penetrating damp or condensation affecting the lower levels of masonry walls.  Modern materials and techniques may be used to achieve the same goal, and many environmental damp control systems & products are available on the market to allow the cost-effective provision of through-ventilated dry lining systems, including specialist plasterboard systems and plastic ‘cavity drainage’ membranes.

Once a damp survey and a report is completed the causes of any damp problems in a building will be apparent.  To prevent dampness from worsening immediate actions should be initiated to prevent further moisture ingress to the structure of the building and to increase ventilation within the affected areas of damp.  These two actions alone can be used to ‘mothball’ a building which, for whatever reason, cannot undergo full damp-proofing remedial repairs.

‘Mothballing’ essentially entails instigating systems that will minimise further water loading of the suspect areas of the building and at the same time improving the rate of drying of damp areas.  A range of different types of techniques can be used for example:  1. correcting all defects in rainwater systems (i.e. clearing out gutters, making temporary repairs to valleys and providing suitable overflows etc.), 2. correcting other building defects which allow water penetration, for example defects in lead work and inadequately pointed stonework, defective windows and their pointing.  3.  Unblocking chimneys and re-capping thus allowing ventilation of flues, unblocking any external ventilation systems, opening up fireplaces.  4. Increasing underfloor and general building cavity ventilation by opening up sub-floor airways, removing single floorboards next to walls, making slots in walls at ceiling and floor level, installing hatches into ceiling voids. 5 Checking ventilation in roof voids and encouraging through (or cross) ventilation where appropriate by the installation of roof vents or adapting the construction of eaves.  6. Removing floor coverings and moving clutter away from walls.  7. Exposing internal down pipes, checking for water tightness and repairing as necessary or diverting water streams away from walls into suitable moisture sinks.

When it comes to protecting your property against rising dampness & timber decay and any other form of dampness found in a house our damp & timber decay specialists are right there with you and have been for nearly 30 years.  Our in-depth damp surveys will correctly diagnose any damp wall issue be it failed damp-course or damp-proof course been bridged, which can lead to water ingress to walls causing penetrating damp and condensation.  This is where accurate diagnosis is imperative so that the appropriate damp control treatments are used thus avoiding the cost of having another chemical injected damp-proof course installed in the walls of your house, flat or any other property.

If you require a damp and timber decay survey /report on a house or flat  to satisfy your mortgage loan provider or yourself, call Damp Aid on your local number (found here), alternatively to arrange a survey fill in our survey request page or if you have any questions about environmental dampness control you can email us through our contact form.


Damp survey, timber survey for house purchase, combined damp and timber survey, specialist timber and damp reports for mortgage providers, damp-proofing quotation and woodworm treatment are provided by Damp Aid UK in the following North West, Midlands and South East regions / areas
 Birmingham, Cheshire, ChesterWrexham, Lancashire, Liverpool, London, Manchester,
Merseyside, Middlesex, North Wales, Shropshire, South East England, West Midlands, Wirral
& Yorkshire