Building Defects Investigations - the correct procedure

Unscientific investigation and imprecise reporting is potentially more descriptive of the level of competence of the surveyor than of the condition of the surveyed building.

A Trading Standards office requested the preparation of evidence for the prosecution of a damp-proofing company. 

The company under investigation held rising damp and groundwater to be unrelated.  From this, they offered a new ‘quick fix’ for damp walls.  They attracted custom by promising to cure damp without inconvenience to occupants.  Troublesome damp-proof courses could be ignored as they played no part – an approach which was as attractive as it was unscientific.  It was not, however, simply the technical merit of their ‘cure’ which was being investigated but the adequacy of their surveys and advice to customers.

They operated by carrying out free surveys.  With each survey report, they confused the potential customer with a profoundly impenetrable description of the mechanisms of rising damp and the working of their ‘cure’.  This mystery dressed in scientific clothing aside, their reports followed an all-too-common pattern, being based on the ill-informed use of electrical-resistance moisture meters. 

To evaluate their work, their survey of a traditional, solid-wall, brick, terraced house, was studied.  The house was typical of its age and construction.  It exhibited the usual limited resistance to damp, suffering minor intermittent problems which varied with the seasons. 

Their survey report showed commendable consistency, being as unscientific in the interpretation of the moisture meter readings as it was casual in describing the process of investigation and obscure in explaining cause and remedy:

  • no check on the meters accuracy was reported,
  • the calibration of the meter was not given,
  • no check for contaminants, such as salts, was recorded and
  • the degree of dampness was over-reported because the meter was calibrated for use in wood but was used to measure moisture in plaster, and the results interpreted as direct moisture content readings.

A check for salt deposits, where moisture readings are interpreted as symptomatic of rising damp, is fundamental.  The presence of surface salt deposits makes electrical-resistance moisture meter readings unreliable.  Conversely, the absence of such salts reduces the likelihood of rising damp being the cause of the moisture found.

Isolated moisture measurements alone rarely show the cause of the dampness.  Corroborative evidence is required and is often readily obtainable by, for example, taking a moisture profile of the suspect wall.  Clarity, thoroughness and completeness are good watchwords for reporting defects investigations.

In the presentation of his findings, the company’s surveyor made clear his lack of understanding of scientific technique, whilst failing in his objectives of demonstrating the presence of rising damp and the appropriateness of the remedial works he proposed.