Condensation Explained
Condensation is regarded as a problem associated with old and new windows. Commonly seen on the inside pane of glazing, new high performance sealed units and windows have resulted in condensation sometimes forming on the outside pane.
Internal and external condensation is caused by the same process
This is atmospheric moisture condensing on cold surfaces. This can be commonly seen as dew on grass, moisture settling on cold bottles brought out of the fridge, car windows misted over outside on colder mornings and many other instances of this occurrence that are understood and widely accepted as being normal.
Warm air can hold higher levels of moisture, often described as humidity. Cold air holds less and if the temperature drops, cooler surfaces such as glass in windows, will offer a perfect place for moisture to condense onto. The moisture has not seeped out of the bottles, car windows or glass but has condensed onto the cold surface as the ‘dew’ point is reached. The dew point being the temperature where the local atmosphere can no longer hold the moisture.
Internal condensation
A common
complaint from residential
customers is that the
condensation they experienced
with their old windows is still
happening with their newly
installed windows. As described
above, the moisture is not
leaking out of the windows. The
reason why the internal
condensation occurs is based on
a number of variable factors
that are out of the window
fitters’ control. The moisture
is in the air within the
room/building and not in the
windows/glass. Factors to
consider include:
Moisture arising in the dwelling
from:
• Cooking
• Bathing
• Drying clothes without
extraction
• New decoration
• Newly plastered walls and
newly laid concrete flooring
• Poor or no ventilation
• No extractor fans in
bathrooms/kitchens
• No trickle vents
• Never opening windows to allow
air circulation
External condensation
Low Energy
efficient windows are high
performance and is related to
insulation and reducing heat
loss. This has in turn created a
phenomenon known as external
condensation that can be as
problematic to homeowners as
internal condensation.
As the name suggests, this is
where condensation forms on the
external pane of the glazing.
Although this can be worrisome,
the condensation is an
indication that the windows are
working well and reducing heat
loss. Again, the condensation is
not leaking out of the windows
or glass but is atmospheric
moisture reaching its dew point
and forming on any available
cold surface.
The new high performance windows
and glazing are preventing heat
loss through them. This means
that the outer pane is no longer
kept warm by heat loss (as in
older windows) and therefore by
being cooler, presents a large
area where external condensation
may form. A similar process is
snow on rooftops. Good loft
insulation prevents heat loss
and the snow remains on the roof
of well insulated homes longer.
Poorly insulated homes can be
seen with little or no snow upon
them.
External condensation usually
occurs at certain times of the
year under particular weather
conditions. This is usually when
the seasons change from winter
to spring and autumn to winter.
This usually results in warmer
days and cooler nights. The
overnight drop in temperature
cools the outer pane and gives
an area for moisture to condense
on to should the humidity be at
appropriate levels.
At times, some windows in a home
may have external condensation
whilst others don’t. This can be
due to the aspect of the window.
Northern facing aspects often
experience higher levels of
external condensation because
they get no direct sun in the
morning which usually evaporates
the condensation. Also,
sheltered windows, such as one
side of a bay window near a
porch for example, can have
condensation whilst a window in
the same bay may not. This can
be due to air movement/wind that
can pass over the exposed window
taking moisture with it but not
reach the more sheltered
aspects.
Normally the external
condensation is short lived and
only occurs on cool mornings.
Often it may have evaporated in
the early hours before a
homeowner opens the curtains and
never be seen. In extreme
circumstances as in sheltered
northern facing aspects, with a
cool night and high humidity,
the condensation may occur more
or stay longer.
Associated condensation issues
A regular
query we receive at Misty Glass
regards ‘Condensation
Patterning‘. This stems from
condensation on the glass
surface and the appearance of
various shapes within the
condensation.
During manufacturing, the glass
is moved around in sheets
measuring approximately 3m x 6m
and processed in to
approximately 3m x 2m sheets
that can be handled and move
around the factory. This
transportation is mainly done
using suction cup transporters
that allow the picking up of
large cumbersome sheets of glass
without damage or risk to both
staff and glass. This is a
vacuum suction cup and can be
various sizes and shapes
depending in the process being
done. Some are circular and
around dinner plate size
possibly 6 circles in 2 lines of
3, or smaller saucer sizes. the
processing equipment has some
oval shaped cups that again move
and hold the glass whilst
processing.
Post processing includes the
application of an identification
label that is rectangular
measuring approximately 12cm x
8cm and protection pads
approximately 2cm x 2cm.
All these processing,
identification and protective
items may leave slight residue
on the glass surface. These
cannot be seen in normal dry
conditions but being hydrophobic
deposits (repelling moisture),
they appear as clear
shapes/marks in the glass when
condensation is present.
This does not represent a fault
in the glazing but is part of
standard manufacturing
processes. This is normal and
over time they will fade.