Condensation

Condensation is water droplets that form when water vapour comes in contact with a cool surface. If condensation forms in wall, roof or floor cavities it can lead to serious mould issues, ineffective insulation, and structural damage.

Condensation and the movement of water vapour are usually managed by the appropriate placement of vapour barriers or vapour permeable membranes. Vapour barriers are a material that blocks all vapour and condensation, while vapour permeable membranes will only block condensation or water droplets while allowing the passage of water vapour in damp air.

Historically, Australian houses were poorly insulated and very leaky and draughty, which meant that condensation was less of an issue. With minimum standards improving, beware of old-fashioned attitudes or a lack of awareness regarding water vapour migration in wall and roof cavities.

The most important thing to know about condensation and water vapour movement is that it varies between the many regions and climates in Australia, as well as site microclimates and even within the construction and cladding system you’re using. The National Construction Code has provisions for condensation management and the ABCB Condensation in Building booklet is an excellent resource that examines the complexities around condensation in more detail.

I have almost a decade of experience designing and specifying for condensation management in cool-temperate climates. My approach is to use best practice energy-efficiency and draught-sealing techniques to drastically reduce draughts (and therefor condensation) into wall and roof cavities, and eliminate any dew-point surfaces in your home (like you might see on single-glazed aluminium windows). I then specify a vapour-permeable membrane to both wall cavities and roof cavities, followed by a drainage cavity, to safely dry and eject moisture within the home's structure.

This Renew article by Jenny Edwards further explains good condensation management in new homes.

Where to find more

The information above is extracted from my book, 101 Things I Didn't Learn in Architecture School; And wish I'd known before my first job.

While the book is written for students and graduates of architecture, it is also an excellent handbook for anyone embarking on their own project. We provide a free copy with every on-site briefing and feasibility meeting, or you can purchase your own copy here.

Another great resource on basic principles in Australia is the YourHome.gov website which is free to access.