What is Rising Damp?

Rising damp is distinct from other forms of dampness and moisture, such as rain penetration and condensation, which require different solutions.  This damp problem is not limited to the UK, but is found throughout the world where there is moisture present in the earth below a building.

Rising damp is the upward movement of moisture through walls, and sometimes floors, by capillary action from below the ground. It occurs at ground floor level in lower portions of external and interior partition walls. The height to which rising damp will rise depends on the size of the capillaries within the building material, the amount of moisture in the ground (water table level) and the evaporation rate from either face of the wall surface. As a general rule, the smaller the capillaries of the structure , the higher the water will rise. However, the height of rising damp usually does not extend much further than approximately 1 metre above ground level.

Modern buildings, in Great Britain, prevent rising damp with a system of damp proofing barriers – a physical damp proof course (DPC) has been required in walls since 1875 and damp proof membranes (DPM) in floors from the 1960’s. Most old buildings lack these and therefore rising damp can occur.  However, the presence of a damp proof course does not guarantee that rising damp will not occur.  If the continuous run of the dpc has been bridged or broken then dampness can appear in the wall.

Rising Damp Symptoms

Rising damp is fairly slow to develop and may be present for several years before any symptoms become apparent.  Eventually it may show as a tide-like damp stain on the wall with little or no damage above, but below the paint may be blistering, wallpaper stained and peeling, the wall plaster damaged and skirting boards showing signs of timber decay. External signs of rising damp are darkening of the lower brickwork, white salt marks and even spalled (damaged) brickwork. Floors can display moist patches and damp staining.

Rising Damp Survey

Before considering the installation of a chemical damp proof course to cure rising damp, the DampAid specialist surveyor will carry out a damp survey to assess the damp problem and ascertain the exact cause of the dampness or moisture and establish the need for rising damp treatment.  Factors such as high external ground levels, poor surface drainage, defective gutters and down pipes can all cause the damp proof course to be bridged, leading to the symptoms of rising damp.  (How extensive is Rising Damp?) By addressing any or all of these defects and allowing the damp wall to dry out naturally, then in most cases the need for a chemical damp proof injection or damp proof course is avoided. Only as a last resort, is a chemical damp proof course installed.

Should the DampAid surveyor, after carrying out a thorough inspection both internally and externally, and eliminating all other causes such as condensation and penetrating damp, diagnose rising damp, then he will assess the extent of the dampness and the need for replastering.  A damp report and/or damp quotation will be provided outlining the most cost effective solution or treatment to the damp problem.

Rising Damp Treatment

As rising damp experts we will carry out the most appropriate treatment to cure the rising damp problem.

Installing a chemical damp proof course (dpc) involves the drilling of the brickwork / mortar to pre-determined depths of external and/or internal walls and then injecting the damp proof course fluid.  A chemical damp proof course provides an impermeable barrier at low level in the structure to prevent further rising damp occurring. This is the most common form of damp proofing used nowadays.
(The BRE - Building Research Establishment - gives advice to consider only methods of damp proofing that have been awarded an Agrement or other third-party certificate. Chemical damp proof injection has an Agrement certificate and is the most cost effective method of providing a damp proof course)

 
The Cost of Treating Rising Damp

We are often asked - How much does rising damp treatment cost / How much does a damp proof course cost?

The cost of treating rising damp or the cost of a damp proof course (damp proofing) varies from property to property.  Firstly, a damp survey has to be carried out by a fully qualified CSRT damp surveyor to correctly identify the dampness and determine if it really is rising damp in need of damp-proof treatment.  Other sources of moisture have to be eliminated, such as penetrating damp, condensation, plumbing leaks etc. before even considering if rising damp is present in a property.  The construction of the building also has to be taken into consideration.  

Therefore there is no standard damp proofing cost as each individual property is different from the next and damp proofing prices differ between each individual timber damp proofing company and the damp proofing system used.

Damp Proof Replastering

This is required to remove all salt contaminated and damaged plaster.  Visibly unnaffected plaster may be left to see if it dries following the damp proof course treatment.

There are other damp proofing systems available to control further rising damp such as:

Diffusion System. This system involves the slow diffusion of a damp proofing cream into the wall, which then forms a water repellent barrier to prevent further rising damp.

Osmotic damp proof course (Electro-Osmosis). This involves inserting a continuous titanium band in the mortar joint and the insertion of electrodes. It relies upon an electrical supply to prevent further dampness from rising up the wall, but the band and electrodes are easily damaged.

Physical Membrane or Physical damp proof course (DPM) which, although effective, is laborious and disruptive to install and there is risk of damage to the structure. It is also difficult to install into party walls and impractical with random rubble walls.

Further Reading:

Building Research Establishment (BRE) BR466 - Understanding Dampness 

Building Research Establishment (BRE) Good Repair Guide 6 - Treating Rising Damp in Houses - January 1997 

BRE Digest 245 - Rising Damp in Walls:  Diagnosis and Treatment - January 1981 

RICS Books (p.151) - Remedying Damp - by Ralf Burkinshaw 

Building Research Advisory Service - Technical Information Leaflet TIL 47 - August 1982 

Estates Gazette - Understanding Housing Defects - 1998 

BRE Good Repair Guide 5 - Diagnosing the Causes of Dampness - January 1997 

English Heritage - The Repair of Historic Buildings - by Christopher Brereton