Civil Engineering Reference
In-Depth Information
The air cavity method
The final method is based on ventilating out moisture that has penetrated the
wall. This problem is most likely to occur in rooms that have a very high
moisture content, or where there are materials of low moisture capacity com-
bined with high damptightness in the wind-proofing membrane. Moisture
needs to be taken care of before it can condense. The dewpoint, where the
temperature is so low that saturation can occur, needs to be identified. There
are ways of calculating this, but they have proved to be unreliable in practice
as the climate is not very predictable. The air cavity can be either narrow or
wide. One solution is cavity wall construction where the cavity is of a large
volume, with a low temperature function, such as a conservatory or storage
space.
Damage due to damp
Damage due to damp can be recognized through mould or the smell of mould. Other
odours can also be caused by damp, because damp can cause gases to be emitted from
glue, paint, mastics and other products.
Mould in organic materials can occur at a relative humidity of 90 per cent. Timber with
a 20 per cent moisture content is easy prey for different micro-organisms. Materials that
are not hygroscopic are often covered with a thin film of water in a damp atmosphere. The
organic glue additives and oils in mineral wool can suffer strong attacks. Traces of mould
can reach inside through cracks in the vapour barrier.
When the damage is done, the damaged area has to be removed and all the materials
changed. The smell of mould can linger even after the damage has been repaired. This
can be removed by ozone treatment. Ozone is, in fact, quite damaging to health, because
it corrodes the inhalation routes in the body, and the gas will destroy plastic materials in
the building, including the vapour barrier.
Air-regulating materials
Wind-proofing a building takes place in two areas, topographical and other wind
breaking effects in the surroundings, and a wind-proofing membrane forming
part of the building's outer skin.
Adjusting to the climate and external windbreaks
Nearby buildings, fencing, mounds, plains, mountains and vegetation regulate effect of
wind on buildings. If the average wind speed around a building is reduced by 1 m/s, it is
possible to reduce the energy requirement by 3 per cent. In the Norwegian coastal town
of Kristiansund, where the average wind speed is 22 km/h (Beaufort scale 4), the loss of
heat for an unscreened building through infiltration is 40 per cent greater than for a
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