Rising dampness


Property Remedial Articles - Olympic Construction

What is rising dampness?

Rising dampness: Is the upward movement of ground water through permeable building materials by capillary action, the level rising dampness can rise is affected by many factors.

  • The water rises through a series of inter-connecting pores within the structure by a process termed ‘capillarity suction’ in simple terms a porous masonry acts like a wick.For rising dampness to occur the suction of the wall must be greater than the suction of the ground otherwise water will not rise.
  • Evaporation will have an effect on the height rising dampness will affect a wall.
  • Gravity will have an effect on the height rising dampness will affect a wall.
  • The Porosity of material the wall is constructed from, will have a major effect of the height moisture will rise.
  • The construction and the thickness of the wall structure, will also have a bearing.

How rising dampness affects a property

Rising dampness can affect a wall for many reasons, the simplest reason being the omittance of an effective damp proof course. The Public Health Act of 1875 introduced the requirement for a dpc in walls to prevent rising damp. The adoption of this Act into local bylaws took some time, though some enlightened builders were already providing a dpc before 1875.

Building defects such as the bridging of the installed damp proof course by plaster or render having been taken down below the installed damp proof course level, raised external path level or blockage of the cavity can result in rising dampness affecting a wall structure.




The photograph to the left showing the installed damp proof course bridged by cement render having been applied to the external elevation.



The photograph to the right showing the damp proof course being bridged by plaster have been taken down to the solid floor.

rising damp diagram
When rising damp affects a wall structure, salts contained within the ground water ‘Nitrate and chloride’ being the most common are drawn into the wall and subsequently the plaster by capillary action. In severe cases the plasterwork can lose its key, along with visual evidence of salts, noted by the presence of staining and surface mineral salting.

These salts are hygroscopic ‘These have the ability to absorb moisture from the surrounding environment’ the amount of moisture absorbed being dependent on the type and quantity of the particular salt, and the humidity of the surrounding environment. In a given situation the moisture levels will vary depending on the ambient humidity.

Hygroscopic salts can cause masonry to remain damp even though there is no source of water (capillary) ingress. Wallpaper especially can become very damp solely due to contamination with hygroscopic salts. Sufficient moisture absorption can cause wallpaper adhesive to become soft and sticky, resulting in the wallpaper to peel away from the wall. Where the wallpaper has become heavily contaminated, its surface feels sticky and may look damp/stained.

The diagram above showing a typical example of the salt profile we would expect to find within a wall structure affected by rising dampness.

Rising dampness treatments

There are many treatment systems for rising dampness, how effective these are is mainly subject to the wall construction. But before undertaking any form of treatment the first thing which should be established is the correct cause of the rising dampness and address this/ these issues first, there is no point in installing a remedial damp proofing system, if the original defect, which resulted in rising dampness was a blocked cavity and the cavity remains blocked, as the ground water will simply bypass the installed remedial system and the wall will remain damp, this is where a detailed survey undertaken by an experienced and qualified damp surveyor such as an approved member of the Property Care Association ( PCA) is essential.

The knowledge and identification of dampness related defects has grown extensively over the last decade with a wide range of instruments and techniques which can be used to investigate the presence and sources of moisture in building materials, the processes for diagnosing rising damp in buildings are set out in BRE Digest 245.

An inspection by an experienced and qualified surveyor can be the difference between a correct and incorrect diagnosis of dampness related defects, preventing misdiagnosis of the cause of the dampness resulting in the wrong form of treatment being specified. Chartered building surveyors are usually experienced in identifying that a dampness issue exists, however they often suggest that dampness problems are investigated by a specialist damp and timber surveyor with a CSRT qualification.