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How to prevent damaging interstitial condensation forming

Most methods for keeping out the wind, rain and snow involve wrapping up the building using water and vapour impermeable products such as foil, perforated foil or reflective bubble type sarking. These products help prevent the water from getting in, however they also prevent the moisture from safely getting out - which can result in damaging condensation forming on cold surfaces within the roof space and wall cavities.

The new era of energy efficient buildings make better use of the roof space and stud frames, accommodating higher levels of bulk insulation and the implementation of air tight building practices. However, failure to consider the correct use of thermal insulation, vapour control layers and breathable membranes at the design stage has revealed a widespread increase of condensation forming inside the layers of the building envelope, particularly in cold and temperate climates and high humidity buildings where there are higher concentrations of water vapour.

Moisture is the number one enemy of most building materials. It only takes a small amount of consistent moisture to cause rot and corrosion of load bearing timbers and ferrous metals. To make matters worse there is a danger that moisture can build up in the insulation causing loss of thermal effectiveness. This can also lead to health problems for the occupants caused by mould springing up and spreading unnoticed within the roof space and walls.

To reduce the risk of condensation forming where it is not wanted, roofing and wall grade breathable membranes are now available in Australia that have a long and proven track record from overseas.  A breathable membrane installed on the cold side of the insulation does much the same job as conventional sarking such as keeping rain, snow and dust from getting into the roof and wall cavities, but also lets the vapour escape, allowing the building to breathe.