Understanding Damp, Condensation and Mould

High humidity, condensation and mould are primarily winter problems which occur when the outside temperatures fall combined with rising internal humidity.

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In winter, sustained periods of low temperature have a colling effect on the fabric of our  buildings thus making the walls, roofs, windows and doors much colder. Many traditional period properties were constructed absent from insulation and are difficult to efficiently insulate retrospectively as such, older buildings are often at greater risk of condensation and mould problems due to their reduced thermal performance in comparison to more modern buildings. 

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Modern building may also suffer too. Modern buildings are constructed with draught proof double glazing and increased insulation, therefore modern properties are heavily reliant upon the provisions for ventilation to maintain a dry, healthy internal climate. The lifestyle of an average family of four is expected to produce between 6 – 14 kg of water vapour per day just through lifestyle activities therefore, when provisions for ventilation are inadequate, there is a risk that humidity levels will rise if the building fails to effectively manage water vapour produced during occupancy.

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The origin of the excess water vapour contributing to a condensation/mould problem is almost always from basic ‘occupancy activities’, ie, cooking, washing, breathing, most frequently associated with a insufficient ventilation, intermittent or inadequate heating, etc.

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Controlling the internal humidity requires a balance between moisture production, temperature of the air and surrounding surfaces and of course maintaining provisions for ventilation. Minor problems can in some circumstance be controlled with lifestyle changes, although the design, orientation and construction of the building may also increase the risk of such problems, therefore, improvements in heating, ventilation and increasing insulation may also be necessary.

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Prolonged high humidity and condensation will inevitably lead to the germination of mould spores which are present in abundance around our homes. Spores that germinate and colonise may cause damage to the building fabric, internal decorations, furnishings and belongings.  In addition, vulnerable people, particularly those with ill health (weak or compromised immune systems) may also find warm, humid environments particularly those polluted with moulds, MVOC's (micro volatile organic compounds) and other contaminants that aggravate respiratory illnesses, uncomfortable and potentially dangerous.

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Mould spores are omnipresent, therefore present in abundance in every building however, spores will only germinate when conditions for growth are suitable. The ideal conditions for germination require three basic elements, these being a supply of food, oxygen and water.  As food and oxygen are present in almost all environments, the key factor for germination and sustained growth is inevitably moisture.

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Some moulds species (‘primary colonisers’) will germinate on substrates when exposed to conditions of just 75-80% relative humidity. Growth may also be fairly rapid, just 24 -72 hours. As the relative humidity against any surface increases so does the risk (‘secondary’ and ‘tertiary’ colonising moulds). It’s important to understand that moulds only require high humidity for germination the presence of physical water i.e condensation is not always necessary factor.

  

Between the months of October to April (condensation season) it is recommended the air temperature internally is maintained between 18°C - 21°C and occupants should ensure heating thermostats are set to a minimum of 16°C.  External walls of the building should remain warm from heating and improvements with insulation should help to ensure the building retains heat efficiently. It is important that long draped curtains or the placement of large items of furniture against walls are avoided, as these will restrict heated air currents over the surface, thus the walls behind will generally be cooler and vulnerable.

Internal relative humidity levels should also be maintained between 40% and 60% and it is essential during the cooler months when the windows and doors are usually kept closed that provisions for ventilation are adequate.