If you consider buying a high-risk home, e.g. a home with monolithic
cladding built in the late 1990s, or if a non-invasive pre-purchase inspection
suggests there might be a watertightness problem - and you are still interested
-, having additional checks done is highly advisable.
There are invasive and non-invasive methods. Invasive ones
require the permission of the owner to carry them out, which is unlikely to be
given if you request destructive checks that leave unsightly traces.
Using a moisture meter - non-invasive method
These small electronic devices are held against the wall or ceiling.
Their two test probesmeasure the density, or the electrical
conductivity, of the timber framing behind it. This testing method
leaves no traces.
However, moisture meters were not designed for the purpose of checking
timber moisture behind gib board or other internal linings, but for taking
moisture readings on building timber directly, e.g. in timber yards or when the
timber framing is up. Therefore correct interpretation of the conductivity
readings requires a high degree of experience. Also the readings can
easily be skewed by cables or metal parts located inside the wall and
need to be compared against a reference reading.
Using a moisture meter - invasive method
Moisture meters can also be used in an invasive way by drilling holes into
the cladding and inserting longer test probes directly into
the timber behind it. This method gives accurate readings but leaves
probe holes, commonly referred to as snake bites, in the wall.
The holes can be filled again but usually remain slightly visible.
Destructive testing
When a lot of signs suggest there is a moisture problem, the most reliable
method of testing is to remove part of the cladding by cutting out a
hole and taking samples of the timber framing. This is obviously not
a feasible method for pre-purchase inspections.
Destructive testing is usually done by home owners wanting to carry out
remedial work or start a formal claims process.
Thermal imaging with infrared cameras - non-invasive
method
Thermal imaging shows the difference in temperature on surfaces (and can
therefore be used to determine the level and location of insulation in walls)
and any moisture present. However, it only workswhen the
moisture is actually there, for example when it rains or there is a leak from
a burst pipe and the water is actually seeping out. It does not pick up
moisture spots that have already dried away after sun exposure or heating a
room to dry the area out.
Thermal imaging can give back false-negative or false-positive results and requires
a high level of experience to interpret the readings correctly. It is
still a good method to "see" what's behind the walls and is usually
followed up by targeted moisture meter readings.