Damp investigations

It is important to take a dampness investigation as far as you can, but in the context of pre-purchase surveys this is not always possible. With this in mind, a staged approach has been devised that links up with the various types of pre-purchase survey.

• Stage 1 (the visual inspection) and Stage 2 (investigation using a moisture meter) include the techniques used by surveyors carrying out pre-purchase inspections.
• A Stage 3 investigation expands on the work done at Stage 2, and uses the full range of moisture meter accessories that are available. In a pre-purchase survey it will sometimes be necessary to expand your investigations to the Stage 3 level.
• A Stage 4 investigation involves opening up and sampling. This inevitably results in damage to decorative surfaces. It also means the use of specialised equipment.

Our overall objective in adopting this approach is to give you a thorough understanding of what can be achieved, sometimes in a short space of time. By providing you with detailed explanations of more 'advanced' techniques, you should not only be able to apply these appropriately but also be better placed to advise clients or to commission specialists to carry out additional tests.

A specialist dampness investigator will take quite a range of equipment to site and, in most cases, would pursue the investigation to whatever stage necessary to track down the cause of a dampness problem.

In practice, surveyors do not rigidly adhere to these 4 stages. You will often find that parts of a property – sometimes just 1 room, or part of a room – exhibit symptoms of a dampness problem for which there is no obvious cause. When this happens, your investigation may be intensified from Stage 2 to Stage 3 and sometimes from Stage 3 to Stage 4 as you seek to identify the cause. However, understanding the range of procedures and equipment available for each level will help you to put your own survey practice into perspective. Moreover, as surveyors become more familiar with instruments such as the carbide meter it is likely that the techniques explained under Stage 4 and illustrated in the case studies will be more commonly carried out by house surveyors.

On the basis of known limitations of surveying equipment described in this methodology, it is not possible to confirm rising damp in walls beyond reasonable doubt, even after you have completed a Stage 4 investigation. Many mistakenly use a positive nitrates result as proof of rising damp; but salts tests on their own cannot prove this (see Surveying equipment and tests). Some insight into the chemical constituents of the ground, the water and the building materials is needed in order for you to single out the subsoil as the likely source of dampness. (Confusingly, typical textbook moisture profiles for rising damp are similar to profiles for penetrating damp and plumbing leaks found in the field.)

In the following sections the 4 stages are described in more detail. Before embarking on any dampness investigation, to whatever level, you are advised to read Surveying Safely and to be thoroughly familiar with the general guidance given elsewhere in this section and by other standard texts. The investigation of dampness in buildings involves use of equipment that is continually changing and improving, and you will need to take on board any methodologies that develop as a result of research in this area, as well as the changing expectations of clients. Surveying to Stages 3 and 4 may require you to undertake additional training.

Dampness diagnosis is not an exact science. The more closely you investigate the greater the chance of correct diagnosis. To put things in perspective, the 'professional opinion' on dampness arrived at after a Stage 2 investigation could be quite correct in 7 out of 10 cases. However, the more intensive investigation would further improve the accuracy of diagnosis to achieve correct diagnosis in more than 9 out of 10 cases.

Although not a 'stage' in the strict sense, we must also mention the role of monitoring.

Monitoring is a powerful technique when you are trying to eliminate potential moisture sources. Monitoring needs owners, occupiers and surveyors to be more patient: the diagnostic process may require you to apply a remedy then monitor its performance over time.