Building Related Questions
What is the Wood Moisture Equivalent (WME) scale as used on Protimeter
Protimeter moisture meters are calibrated for wood but are also suitable for
measuring moisture levels in other materials. They are highly versatile tools
for assessing the moisture condition of a wide range of non-conductive
In wood, the instruments measure the material’s actual
percent moisture content (%H2O). When testing material other than wood, the
meters measure the wood moisture equivalent (WME) value of the material. WME is
the moisture level that would be attained by a piece of wood in equilibrium with
the material being tested. As the critical moisture levels for wood are known,
WME measurements enable the moisture meter user to establish if materials are in
a safe air dry, borderline or damp condition.
What is Relative
Relative humidity (%rh) is the degree of saturation – or the amount of water
vapor that air contains – relative to the amount it would contain if saturated.
This is often expressed as a percentage, so saturated air at a given temperature
If air is warmed, the amount of water vapor it could hold at
saturation is increased. Consequently, the %rh value falls, even though the
actual amount of water remains constant. Similarly, if the air is cooled, the
amount of water vapor it can hold is reduced. Consequently, the %rh value rises.
Condensate forms when there is an excess of water in saturated
What is Equilibrium Relative Humidity (ERH)?
If a dry and absorbent material, such as wood or brick, is placed in a very
damp environment (high %rh) it will absorb water and its moisture content will
increase. Conversely, absorbent materials with high moisture content will lose
moisture to a dry environment (low %rh).
The movement of moisture from
material to environment and vice versa continues until the vapor pressures
(within the material and the environment) have equalized. When this condition is
reached, the moisture level of a material can be expressed in terms of
equilibrium relative humidity (ERH).
ERH techniques are very useful for
assessing if structures are in a dry, borderline or damp condition. For example,
when the ERH of a concrete floor falls to 75%, a flooring contractor knows that
it has dried sufficiently for a decorative floor covering to be
What is Dewpoint?
Dewpoint is the temperature at which a sample of air becomes saturated.
Condensation forms on surfaces whose temperature is equal to or lower than the
prevailing dewpoint temperature.
At what level of WME is a
material in a wet or dry condition?
- <18% (Green Zone) - The material is in a Safe Dry condition, moisture
related problems of decay/deterioration will not occur.
- 18% - 20% (Yellow Zone) - The material is in a Borderline condition,
decay/deterioration may occur under certain conditions.
- > 20% (Red Zone) - The material is in a Wet condition,
decay/deterioration is inevitable in time unless the moisture level of the
material is reduced.
I suspect my %WME readings in a wall
are too high, what should I check?
Artificially high moisture meter readings may be obtained in material that
- has been heavily contaminated by hygroscopic salts, or
- in materials that are conductive by their own nature.
If the material being tested is conductive an
alternative moisture measurement technique should be used. A hygrometer could be
used to measure the material’s ERH, or its actual moisture content could be
determined with an Ashworth Instrumentation Speedy™ tester (see product