Ventilation of internal spaces

To avoid problems with fungal decay, high humidity air within the building envelope must be dispersed by ventilation.

Large amounts of water vapour (more than 15 litres each day in a typical house) are generated within buildings, particularly from bathrooms, kitchens and laundries. This causes high levels of humidity, particularly in modern buildings that tend to be well sealed for energy efficiency. If areas of high humidity are allowed to persist, particularly in conjunction with high temperatures, fungal decay and mould growth will result.

Under-floor spaces have minimum ventilation requirements specified by law. Care must be taken during building to ensure that ventilation is not blocked by careless construction practice, such as allowing mortar from brick cladding to contact wall framing.

Bathrooms, kitchens and laundries should not be vented into the roof space unless it is well ventilated. Most roofs are now fitted with sarking, reducing ventilation.

It is often helpful to open windows during the hottest part of the day to allow highly humid air to disperse.

References:

• Timber Datafile P4 – Timber – Design for Durability of the NAFI Timber Manual.
• KR Bootle - Wood In Australia. McGraw Hill 1983

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Timber Research Unit
Department of Architecture
University of Tasmania