How to Identify
the Cause of a Mold and Mildew Problem
Mold
and mildew are commonly found on the exterior wall surfaces of corner
rooms in heating climate locations. An exposed corner room is likely to
be significantly colder than adjoining rooms, so that it has a higher
relative humidity (RH) than other rooms at the same water vapor pressure.
If mold and mildew growth are found in a corner room, then relative
humidity next to the room surfaces is above 70%. However, is the RH above
70% at the surfaces because the room is too cold or because there is too
much moisture present (high water vapor pressure)?
The amount of moisture in the
room can be estimated by measuring both temperature and RH at the same
location and at the same time. Suppose there are two cases. In the first
case, assume that the RH is 30% and the temperature is 70oF in
the middle of the room. The low RH at that temperature indicates that the
water vapor pressure (or absolute humidity) is low. The high surface RH
is probably due to room surfaces that are "too cold." Temperature is the
dominating factor, and control strategies should involve increasing the
temperature at cold room surfaces.
In the second case, assume
that the RH is 50% and the temperature is 70oF in the middle of
the room. The higher RH at that temperature indicates that the water
vapor pressure is high and there is a relatively large amount of moisture
in the air. The high surface RH is probably due to air that is "too
moist." Humidity is the dominating factor, and control strategies should
involve decreasing the moisture content of the indoor air.
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