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Most methods designed to keep the rain and wind out, involve wrapping the building in impermeable materials such as foil, steel, glass or other waterproofing materials. Such materials do a great job of stopping the water from getting in, but they also prevent vapour from getting out safely. In the winter, these materials in the roof space or your wall cavities can get wet due to condensation.

If there is condensation on the inside of the windows during the winter then there is a good chance that condensation is also forming unseen on the inside of walls or roof spaces that have been wrapped in foil.

If insulation is not installed correctly in relation to the position of vapour barriers and breather membranes, mistakes can lead to structural damage and health problems for occupants caused by mould springing up and spreading unnoticed within the roof space and walls, resulting in expensive rectification.

If the foil sarking should not be used on the cold outside of insulation then what can be used to wrap the building. The product you will be using goes under the generic name of ‘breathable membranes’. A breathable membrane 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 space and wall cavities, but also lets the moist air escape.

Typically breather membranes are textile products that work much in the same was as Gortex fabric and have a very low vapour resistance of less than 0.26MNs/g. These should not be confused with some perforated foil type products labelled as “breathable”, despite having a vapour resistance more than10 to 70 times the breathable membrane standards overseas.

To allow condensate to drain safely out of the wall to help wall assemblies dry out, common practice overseas is to have avented cavity between the external cladding and the breather membrane. This concept is increasingly being adopted by good builders in Australia.

As we go into winter has anyone seen an increase in condensation, mould or damp issues that can't be explained by leaks?

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