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At 100% RH, saturation point is
reached and, thereafter, any further water vapour introduced
into the air will
be deposited as condensation. Similarly, should the temperature fall,
because colder can support less moisture, the RH will
rise and, again, condensation will form.
Conditions producing condensation.
As explained above, changes in temperature or
in moisture content of the air can
cause condensation to occur. These changes can
occur naturally or
artificially:
Atmospheric conditions. When warm, damp weather follows a period of cold
weather, the fabric of a heavy structure, such as a multi-
storey building of
mass concrete design, which has not been fully or continuously heated, will
not
warm up immediately, but may remain cold
for a relatively considerable period of
time. When
the moist, warm incoming air comes into contact with the cold
surfaces, water will condense upon them, but as the walls warm up, condensation ceases and the deposited moisture evaporates.
Artificial influences. The humidity within an occupied building is usually
higher than outside. People themselves, and many of their activities, increase
the amount of moisture in the air. Moisture is released by breathing, cooking,
clothes washing/drying and by the use of oil or gas fired appliances.
Condensation, particularly in houses and flats, does not necessarily
occur in the room where
the water vapour is produced. A kitchen or bathroom
where vapour is formed may be warm enough to remain free from condensation. The
exceptions to this may be where water vapour forms on single glazed windows,
cold water
pipes or other cold surfaces within those areas. But if the water
vapour is allowed to escape throughout the house/flat into the colder rooms
which may not be heated, or heated for only part
of each day, condensation will
occur on the cold surfaces within those rooms, which may be
some distance from
the source of the moisture.
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Means of reducing condensation.
Remove moisture laden air from the house/flat near to its point of origin. This
will involved the introduction of ventilators into kitchens and bathrooms,
preferably incorporating a Humidistat facility to provide a degree of control
over the operation of the ventilator and, thereby, reduce heat loss to a
minimum. Clearly, before any ventilator can be installed, an opening will need
to be formed into the external wall of the kitchen or bathroom and, so far as
flats are concerned, prior approval will almost certainly need to be given by
the Freeholders or their Managing Agents. The addition of self-closers to the
internal doors can also improve the situation by providing a means of divorcing
the moisture generating areas, such as the kitchen and bathroom, from the
remainder ofthe house/flat.
Reduce moisture generation.
Provide adequate heating at all times. As mentioned above, for any given set of
circumstances, an increase in air temperature will assist in reducing the onset
of condensation.
Improve insulation. By adding an insulation layer between, say, the cold
external walls and the moisture laden internal air, the temperature of the
internal surfaces can be effectively increased, with a consequential reduction
in the presence of condensation. The introduction of a secondary double
glazing system into the window openings will achieve a similar improvement in
living conditions by separating the colder, outer panes of glass from the damper
internal air.
Generally.
The suggestions made above are intended to provide a framework within which to
alleviate condensation as an environmental difficulty. They are based
upon advice given in the relevant Building Research Station Digest (no. 110),
the Building Research Station Report on Tracking Condensation, and the Good
Repair Guide 7 - Treating Condensation in Housing. Where specific problems
exist, it may be necessary to supplement these general recommendations with
further advice from a suitably qualified person or organization. |
