Rising damp and penetrating damp: causing dry rot, wet rot and insect decay

In the UK, a large number of traditional buildings (those built before 1919, which form almost a quarter of our building stock), usually suffer from damp (rising damp or penetrating damp).

This is mainly due to various interventions over the years, including:

• the use of vapour impermeable materials, e.g. cement renders;
• remedial chemical damp proof injection etc.;
• building high ground levels over the years;
• removing rotten timber floors and installation of solid floors; and
• various forms of tanking for damp proofing to deal with the symptoms of damp.

These interventions block the drying pathways (building breathability) and lock the moisture in, resulting in dampness of the building fabric, therefore leading to mould infestation, wood decay fungi attack (e.g. dry rot, wet rots etc.) and insect infestation (including woodworm and death watch beetle) leading to building deterioration.

In many of these old buildings, conventional surveyors recommended extensive chemical injection damp proof courses (which had, in some cases, been installed previously and had already failed). These recommendations were based on the readings of electronic moisture meters. These meters are commonly used to diagnose rising damp, but they often give false readings with certain paint and wall finishes, and fail to differentiate between penetrating dampness, condensation and hygroscopic salts.

However, it must be pointed out that these buildings are breathable (vapour permeable), i.e. while the building fabric lets the moisture in, it also allows it to evaporate when the weather turns dry.

Non-destructive instrumentation, infrared thermography, damp and residual moisture analysis, and spot environmental monitoring combined with the knowledge of building construction, structures and building science and pathology, enabled surveyors and builders to develop cost effective, minimally destructive, sustainable conservation solutions for these historic buildings.

Independent diagnostic non-destructive, environmental surveys as described above will normally lead to the following conclusions:

• Chemically injected damp proof courses were not required and the solution to these problems was to deal with the cause(s), which are varied and depend on the individual circumstances. For instance ground levels may need to be reduced, new lime plaster may be required on the internal walls, dry lining systems may be necessary, or physical damp proof courses may be recommended.
• Remedial chemical treatments including drilling masonry walls and injecting with chemicals for dry rot and wet rot infestation were not required.
• Treating and spraying with toxic chemicals for mould eradication was not required.
• Spraying chemicals for woodworm infestation was not required.