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Internal condensation of double glazing
units
Double glazing units may be subject to inte-
rior condensation which is determined by:
•
The moisture produced by human acti-
vity in the house
•
Heating of the room
•
Ventilation conditions.
If condensed water from a double glazing
unit runs into the sash/frame construction
it may lead to the formation of mould fun-
gus or, at worst, decay fungus on the wood.
There are a number of things/conditions
which may cause condensation in the house.
Notice especially the following:
•
That new windows are considerably more
airtight than old ones. When new windows
have been installed, the house will need more
ventilation than before
•
That newly-built houses must be ventilated
more often than old ones. It may take more
than a year to dry a new house properly. This
is also the case when additions have been
made or the house has been renovated
•
That an adult person – or a medium-sized
dog – releases approx. 2 litres of water per
day
•
That cooking, bathing, laundering and drying
from two adults and two children can easily
produce 3-5 litres of water per day
•
The problem with humidity increase when
the room temperature is lowered and decre-
ase when the room temperature is raised.
Even lowering of the temperature for a short
period of time (e.g. at night) can cause the
formation of condensed water on the glass.
•
That heavy curtains and broad window
boards/frames can make the air stagnate at
the glass causing cold and moist air to form
condensate on the glass
Double-glazing
•
That insufficient ventilation causes a bad
indoor climate which may lead to coughing,
headaches, smarting eyes, rashes and respi-
ratory allergies.
•
That a house which has been subject to a
high level of humidity for a period of 8 to 14
days should be ventilated thoroughly. This
is done by having 2-3 windows open in their
ventilation position day and night and, at the
same time, raising the temperature 4-5° C
above normal for 8 to 10 days. You can also
leave your range hood on in the kitchen day
and night
•
That on days with calm, sunny weather, the
sun will supply more free heat than the heat
that disappears during normal ventilation
•
That it is a balancing act to find the perfect
equilibrium between saving energy and
minimising humidity problems.
External condensation of double glazing
units
It is not until in recent years, that we have
seen the problemwith exterior condensation
(
dew) on low-energy units. The problem ari-
ses when emissions to the atmosphere cau-
ses the temperature on the exterior layer of
glass to become lower than the exterior air's
dew-point temperature.
This typically occurs in periods when the
relative air humidity is near 100%. Exterior
condensation of low-energy units typically
occurs in the months of autumn and spring,
usually at night and in the morning, until the
condensation is removed by sun and air. The
problem can be especially noticeable during
the months of April and September. The
problem with exterior condensation is usu-
ally the result of energy saving units having
a very low U-value.
