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Double-glazing
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 activity
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 venti-
lated more often than old ones. It may
take more than a year to dry a new house
properly. This is also the case when additi-
ons 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 dry-
ing 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
decrease 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 wa-
ter 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
•
That insufficient ventilation causes a bad
indoor climate which may lead to coug-
hing, headaches, smarting eyes, rashes
and respiratory 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 tempe-
rature 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 venti-
lation
•
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
