Condensation and the Water Cycle

Written on the 27 October 2020 by George Dahrie

Condensation and the Water Cycle


What is Condensation and how does it form?

Is Condensation considered a building defect?

How to manage condensation.

We asked George Dahrie the Principal Engineer at Noviion Engineering, Here is his response:

Condensation is an increasingly common issue in modern residential buildings as more insulation and glazing are incorporated in structures that aim to reduce air leakage and create energy-efficient buildings. Condensation is the process through which water vapour present in the atmosphere becomes a liquid. This becomes problematic when the water accumulates as the condensate is unable to evaporate as readily as it forms.  The two main consequences of condensation are the generation of health risks through the growth of mould, mildew and other fungi, and aesthetic deterioration of internal finishes. The growth of mould in buildings can trigger respiratory inflammation and infection and in some instances with long-term exposure can worsen asthma and allergic conditions. The presence of moisture deteriorates paint finishes, can lead to swelling and warping of timbers, furniture and wall linings, and cause corrosion of metallic elements.

Water vapour is present in both indoor and outdoor air and therefore given the right conditions condensation can occur. Condensation forms when the water vapour present in the air comes into contact with a surface that us at or below the dew point of the air. The dew point is simply the temperature at which air most be cooled to become saturated, that is for condensation to occur. The dew point is dependent on how much water vapour is contained in the air, with humid air having a higher dew point and therefore a higher temperature at which condensation will occur. Indoor activities that contribute to water vapour increases include; cooking, washing and drying clothes, dishwashing and bathing. This is why it is common for condensation to form overnight during colder months, as these activities are often undertaken throughout the evening and no external ventilation is open or operating and often in conjunction with internal heating. As the external temperature drops and the internal water vapour content of the air increases, condensation forms primarily at and around glazed windows and doors as these elements  are at temperatures below the dew-point with high relative humidity.

While condensation is common and can lead to health, aesthetic and structural concerns over the long-term, it is not considered to be building defect if the design has been carried out in accordance with the National Construction Code. The National Construction Code (2019), requires that either mechanical ventilation (such as kitchen and bathroom exhausts) or natural ventilation must be provided. Natural ventilation is achieved through the provision of external openings such as windows and doors. As stated in the NSW Guide to Standards and Tolerances (2017) "where the requirements of the Building Code of Australia have been complied with, the responsibility for controlling condensation by maintaining adequate natural or mechanical ventilation through the use of openable windows, exhaust fans, or other means, is the responsibility of the owner".

There are numerous ways in which an occupant can assist in managing condensation within a building through controlling of internal moisture levels. These include ensuring adequate ventilation, heating, removal and furniture arrangement.

Adequate ventilation will be achieved through maximising the opening of windows and doors during colder months and restricted opening of windows and doors during hotter periods. During colder months, occupants should attempt to maintain a relatively low constant internal temperature as opposed to periodic heating. The use of dehumidifiers and dry heaters can also assist in controlling the water vapour content of internal air. Additionally, where possible occupants should attempt to place large furniture away from walls to ensure adequate space for the circulation of air.

To find out more speak to Noviion Engineering

George DahrieAuthor: George Dahrie
About: Principal Engineer at Noviion Engineering

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