Meeting the challenges of structural damp diagnosis in older buildings

Abstract

Diagnosing dampness in the walls of buildings that were constructed 100 years or more ago, often using materials and techniques that are very different from those in use today, can be extremely challenging. Despite the availability of a wide range of diagnostic equipment aimed at identifying building dampness, there is no single piece of diagnostic equipment currently available capable of overcoming the wide natural variations found in the field, that is able to reveal excess moisture within structures, and equally importantly, to determine its severity. All too often, damp in walls is misdiagnosed by over-reliance on a single piece of equipment. This equipment often appears to have been designed on the assumption it will be used on buildings constructed from currently available standard materials, which have been assembled using conventional techniques to meet current regulations. However, when using electronic meters to diagnose damp, if multiple measurements are taken using different types of meter, it is possible to overcome most of the limitations of individual meter types along with any tendency to misrepresent the moisture status of older or less common building materials. This paper outlines a method of damp diagnosis for historic and vernacular walls that allows multiple readings, taken with three complementary meter types, to be combined and mapped back onto the building. This method highlights the differences between raised salts and true excess moisture, together with their respective severities and spreads, leaving the surveyor free to apply his/her knowledge of materials science and building construction to identify the most likely causes of any problems revealed and, if necessary, to devise remedial strategies that are compatible with the building. Three examples illustrate how the method outlined can be successfully used on buildings with very different moisture problems.