Condensation & Moisture Control: How it Affects a Building

Moisture content within the fabric of your Home

Our habitat is an extension of ourselves, it forms a protective element from the extreme of the external environment and should harmonise with our need to breathe and at the same decant the spoil from our daily existence. The contaminates distilled and decanted by air contribute a significant part of the breathability equation for the envelope of our home. This impacts on our health and sense of well being.

Good quality housing that has evolved over the generations were naturally adapted to our life and maintained the balance of our needs. Alas the compacting of our habitat combined with the decadence of the modern life style has tipped the balance, and to make matters worse many new building materials create vapour barriers, these barriers upset the naturally designed breathability of our existing quality housing stock and these same vapour barriers have forced the design of new housing to have mechanical means to supply and extract air.

Traditionally the building material element would have its own natural balance of water content and air exchange ability. At peak times this build element would act like a reservoir providing a means to ‘dampen’ air humidity extremes at peak moisture producing periods. Then dispel the excess water over a period of time ready for the next humidity event.

At higher humidity the probability of dew forming increases, once the moisture from the air has changed state to water it is more difficult to move (dry out) as in the process of condensing it has given up its kinetic energy and will now need that kinetic energy to re-evaporate, this evaporation will cause a cooling down of the same surface.

Water dynamics in existing properties where building fabric has become damp over extended periods

The envelope of your home will generally have an internal plaster finish with the primary structure made from brick (or a form of bound aggregate material).

When you have an existing ‘Damp’! condition it will mean all the absorbing materials, including clothes, bedding, carpets etc have also higher humidity levels. This combined with the inner envelope having saturated or near saturated levels means that a drying out period is required.

Unfortunately the drying out period is most likely hoped for in the winter periods when the envelope skin is cooler and the ventilation rates reduced. “Active ventilation measures will need to be introduced to cope with moisture production”.

Another side effect of drying out is that the very high humidities present will cause dew on the humidity sensing heads, this saturation causing temporary low differential sensing levels of automatic humidity control devices.

Each situation will be different, depending on location of sensor, extent of excess moisture in the building fabric, size of room/dwelling (smaller properties will become saturated quicker).


It will take nominally up to one year to dry out conditions of excess moisture in the building fabric.

A shorter drying time can be achieved with increase of sustained temperature and increased ventilation.

Further Information

Heritage House

Controlling Condensation

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