Excess moisture leads to growth of microbes such as moulds, fungi and bacteria, which subsequently emit spores, cells, fragments and volatile organic compounds into the indoor air. Moreover, dampness initiates chemical and/or biological degradation of materials, which also causes pollution of the indoor air. Exposure to microbial contaminants is clinically associated with respiratory symptoms, allergies, asthma and immunological reactions. Dampness has therefore been suggested to be a strong and consistent indicator of risk for asthma and respiratory symptoms.

A wide range of instruments and techniques can be used to investigate the presence of moisture in building materials. When used correctly, they can provide a valuable aid to investigation. The competence and experience of the person undertaking the damp investigation is often of greater importance than the kit he or she carries. Experience and qualified surveyors are the difference between a correct and incorrect diagnosis of damp.

In the UK, well built modern houses include damp proofing in the form of a synthetic damp-proof course (DPC), about 150 mm above ground level, to act as a barrier through which water cannot pass. Slate or "engineering bricks" with a low porosity were often used for the first few courses above ground level, and these can help minimise the problem.

There are many approaches to the treatment of dampness in existing buildings. Key to the selection of an appropriate treatment is a correct diagnosis of the types of dampness affecting a building.

The Institute for Specialist Surveyors and Engineers (ISSE) has produced a level 3 Diploma (i.e. requiring 500 hours of study and assessment) in partnership the regulated educational specialist ABBE which many might think should lead to improvements in standards throughout the industry as far more training and assessment is possible in the extended time available to tutors.

In simple terms rising damp occurs when ground water travels upwards through porous building materials such as brick, sandstone, or mortar, much in the same way that oil travels upwards through the wick of a lamp. The effect can easily be seen by simply placing a piece of porous brick, stone, or mortar in a shallow tray of water and observing how the water is absorbed into the porous material and is transported above the water line.

Rising damp can be identified by a characteristic tidemark on the lower section of affected walls. This tidemark is caused by soluble salts (particularly nitrates and chlorides) contained in the groundwater. Due to the effects of evaporation these salts accumulate at the peak of the rising damp.

The first step in assessing damp is to check for standing water. Removing water with good drainage will remove any form of dampness. Once done, and dampness remains, the next step is to look for the presence of a damp-proof course. One method that is often used to determine if the source of dampness is rising damp is to look for the presence of salts - in particular a tell tale "salt band" or "tide mark" at the peak of the damp's rise. Although this is a useful indicator, it is not completely reliable as salts can enter the fabric of the wall in other ways - e.g. unwashed sea sand or gravel used in the construction.

If there is no damp-proof course and rising damp is suspected  then a number of diagnostic techniques can be used to determine the source of dampness. BRE Digest 245 states that the most satisfactory approach is to obtain samples of mortar in the affected wall using a drill and then analysing these samples to determine their moisture and salt content to assist in providing appropriate remedial building solutions. The fact that this technique is destructive to the wall finish often makes it unacceptable to homeowners. It is for this reason that electrical moisture meters are often used when surveying for rising damp.

In many cases, damp is caused by "bridging" of a damp-proof course that is otherwise working effectively. For example a flowerbed next to an affected wall might result in soil being piled up against the wall above the level of the DPC. In this example, moisture from the ground would be able to ingress through the wall from the soil. Such a damp problem could be rectified by simply lowering the flowerbed to below DPC level.

Where a rising damp problem is caused by a lack of a damp-proof course (common in buildings over approximately 100 years old) or by a failed damp-proof course there is a wide range of possible solutions available. Replacement physical damp proof course, Injection of a liquid or cream chemical damp proof course, (DPC Injection), Damp-proofing rods, Porous tubes / other evaporative methods., Land drainage, Electrical-osmotic systems

A physical damp proof course made from plastic can be installed into an existing building by cutting into short sections of the mortar course, and installing short sections of the damp proof course material. This method can provide an extremely effective barrier to rising damp, but is not widely used, and is considerably longer to install than other types of rising damp treatment.

Injection of a liquid or cream into bricks or mortar is the most common method of treating rising damp.

Liquid-injection products were introduced in the 1950s and were typically installed using funnels (gravity feed method) or pressured injection pumps. The effectiveness of liquid injection damp proofing products is dependent on the type of formulation and the skill of the installer.

In more recent years patented damp-proofing creams have taken over from liquid products due to improved ease of application. As with liquid products these are based on silane/siloxane active ingredients, which line the pores of the mortar to repel damp.

Damp-proofing rods were launched onto the market in 2014. They use similar active ingredients to those found in liquid or cream-based rising damp treatments, but contained in a solid, porous rod. The rods are placed into holes drilled in the mortar course and the active ingredients diffuse along the mortar line before curing to form a damp-proof course.

Whilst there is evidence to suggest that these systems can be useful in moving salts in walls there is little in the way of independent data to demonstrate effectiveness in treating rising damp. The BRE publication "Understanding Dampness" makes the following observations about electro osmotic systems for the treatment of rising damp: "There are two types: active and passive; neither has been approved by a recognised laboratory. By far the greater numbers of systems are of the passive kind, where there is no external source of electricity. They have always been something of a controversial issue. On theoretical grounds, it remains a mystery as to how they can work; their effectiveness has not been demonstrated in the laboratory and field evidence is disappointing

Replastering will often be carried out as part of a rising damp treatment. Where plaster has become severely damaged by ground salts there is little argument about the need to replaster.

BS6576: 2005 states that "the function of the new plaster is to prevent hygroscopic salts that might be present in the wall from migrating through to its surface, while still allowing the wall to dry."

More recently, systems have become available that allow plasterboard or insulation board to be used to Replaster walls affected by rising damp. After the existing plaster has been hacked off the wall, a salt and moisture retardant cream is applied to the wall. The plasterboard is then applied to the wall using a salt/moisture-proof adhesive. Such systems have the advantage that they can be decorated straight away, rather than having to wait several days or weeks as in the case with standard plasters. They also provide a warmer surface that is less prone to condensation than would be the case with standard sand: cement render.

Replastering may not be necessary where salt contamination is not severe. BS6576: 2005 states, "Where the plaster appears to be in sound condition, the extent of plaster to be removed may be minimised by delaying any decision to replaster until the drying period is complete." Avoiding the need to replaster in this way can reduce disruption and mess and has the advantage of allowing the original lime or gypsum-based plaster to be maintained.

It is best practice to delay replastering and redecoration for as long as possible following rising damp treatment, but this obviously creates inconvenience to the occupants of the affected building. BRE Digest 245 states, "While the wall should be allowed to dry for as long as possible, replastering can follow, providing porous decorations are selected. These are usually matt emulsions and water-based paints, both of which will allow the wall to breathe. Application of gloss and vinyl paints or wallpapers should be delayed for at least one year.