Condensation is a critical concern that affects buildings all over the world. In Australia, there has been a drastic increase in both large incidences and serious condensation challenges which, as a result, have prompted not only changes to building design but also an increase in energy efficiency targets across the country.

If not prevented and managed properly, condensation can cause severe issues in construction, both when it comes to the structure of the building and the wellbeing of occupants.

Condensation can create adverse health impacts arising from dampness and mould - both of which are known to cause and agitate respiratory problems. It can also cause extensive structural issues as building materials and cladding become gradually weaker over time, resulting in premature degradation and potentially life-threatening consequences if any major structural elements fail as a result.

Condensation In The Built Environment

Condensation is a result of differing humidity levels between the inside and outside of a structure. That means it generally affects materials used to form the building envelope.

In the most basic terms, condensation is caused by changing levels of relative humidity in changing air temperatures. Warm air can hold more water vapour than cold air and so when warm air - laden with water vapour - begins to cool, it must release that water vapour. It does so by depositing liquid water on the closest cool surface.

In the context of the built environment, this is most often a wall, roof or window. In addition, people occupying the space engage in a variety of activities that can increase the relative humidity within a building - from breathing and talking, to heating, cooking, or taking showers. When this vapour-rich air begins to cool near the envelope of the building, it forms condensation on the interior and interstitial of the building, which can be problematic.

Preventing Condensation Through Insulation

Dealing with condensation issues can be complex, as there are numerous factors to consider. Apart from the activities of the occupants and the building materials in use, the National Construction Code outlines eight climate zones for consideration. 

That said, builders and designers can prevent and manage condensation through a range of strategies, such as adequate ventilation and - most effectively - through high-performance insulation and sarking.

For example, a high-quality bonded foil insulation blanket can provide excellent thermal resistance in metal roofing applications while also creating a vapour barrier to minimise condensation. Products like Fletcher Insulation’s Permastop® Building Blanket offer the dual benefits of a glasswool blanket substrate that is faced on one side with a non-permeable reflective foil laminate.

The glasswool provides excellent thermal performance, minimising heat transfer through the roof. It also offers the added benefits of acoustic damping which is highly desirable in metal roofing applications where heavy rain and hail can otherwise be deafening.

The Sisalation® reflective foil laminate serves as a vapour barrier when taped and is generally installed face down into the ceiling cavity. Here it works in tandem with a ventilated ceiling to regulate heat flow and prevent condensation. In tropical climates, however, the foil faces outwards, directly underneath the metal roofing where it acts as sarking and allows any condensation or leakage through the roof to run off into gutters. It also provides a vapour barrier that stops the transfer of hot moisture-laden air into a roof system.

Vapour permeable roof and wall sarking can also be used to help minimise condensation.  Following recent changes to the National Construction Code, vapour-permeable sarking can be used in non-combustible external wall applications which also acts as a water barrier in walls with a drained cavity.

Here, specifiers should opt for second-generation vapour permeable wall wraps such as Sisalation® Vapawrap vapour permeable wall wrap. It’s suitable for use behind lightweight cladding like fibre cement sheets, weatherboard, timber and brick veneer.

It features a highly permeable membrane, allowing the easy transfer of vapour and minimising condensation, and when installed and sealed with a suitable tape it is also water, wind and dustproof - providing an excellent barrier against the elements in these applications.

Minimising condensation in the envelope of any building is crucial to the prevention of structural degradation and minimising health risks for any occupants. By making smart insulation choices in both roofing and external wall applications, specifiers can not only minimise the potential damage from condensation but create sustainable, energy-efficient buildings in the process. Fletcher Insulation’s Permastop® Building Blanket and Sisalation® Vapawrap+ wall wrap and metal roof perform well in these applications, providing peace of mind for specifiers.