DREADED DAMP NEW RICS GUIDANCE RECOMMENDS A MORE NUANCED APPROACH TO DIAGNOSING DAMP IN OLDER BUILDINGS.
F
or anyone dealing with period properties on a regular basis, a diagnosis of rising damp in a pre-purchase survey is a circumstance that is worryingly inevitable, and is generally taken as something one just comes to expect with
older houses. But should it be this way?
Quite simply, there is a rampant industry-wide
Statements such as “High moisture meter readings recorded to internal surfaces of external walls
overreliance on the use of moisture meters
at lower ground level. Readings are consistent with rising damp”, or “An electronic moisture meter
when diagnosing dampness and specifying
was used … to detect the presence of dampness. High damp readings were noted to the walls in a
damp remediation such as the installation of
number of areas”, are typical. Helpfully, the surveyor will often then recommend that: “Inspections
injected damp-proof courses (DPCs).
by a reputable damp/timber treatment specialist are required and in relation to the rising damp,
Yet, this all flies in the face of established
a chemical injection system is likely to be the most appropriate form of remedial repair”.
guidance on this topic. BS 5250:2011 (Code of
In the face of such professional opinions, the various parties to a sale can find themselves in a
Practice for The Control of Condensation in
quandary. Sometimes sales fall through, purchase prices are renegotiated or purchasers just bite
Buildings) specifically states that: “Accurate
the bullet and accept the often costly recommendations as a fait accompli. The sad reality is that
measurements of the moisture content of brick
such recommendations are often based on an inadequate understanding of traditional building
or mortar cannot be obtained by the use of
construction, a failure to consider all potential causes of dampness, and inappropriate diagnosis
electrical moisture meters because the
of circumstances.
presence of salts increases the electrical conductance of the water, giving falsely high
Don’t read the meter
readings”.
A major problem is the overreliance on and, at times, misuse of, moisture meters when
Furthermore, BS 6576:2005 +A1:2012 (Code of
diagnosing damp problems. Firstly, it is extremely important to note that moisture meters are
Practice for Diagnosis of Rising Damp in Walls
calibrated to measure moisture in timber. They cannot accurately measure the quantity of
of Buildings and Installation of Chemical
moisture in a stone/brick wall. They can only provide an indication of relative moisture content in
Damp-Proof Courses) notes that while: “An
material other than timber.
electrical moisture meter is a useful diagnostic
Secondly, the readings from a moisture meter can be influenced by the presence of metals, wiring,
instrument: ... The readings it gives are
foil-backed insulation, plasterboard or wallpapers. Above all, readings can be influenced by salts,
qualitative. Surface moisture monitoring alone
which are found in many building materials, and particularly in old walls.
cannot give proof of rising damp”. Basically, a moisture meter alone should not be used for
FEATURE Frank Keohane SCSI Building Conservation Accredited Surveyor
18
SURVEYORS JOURNAL Volume 11, Issue 3, Autumn 2021
the diagnosis of rising damp.
