Construction using Building Wraps and Barriers

Whether your home will be passive, industry standard or somewhere in-between the choice of your external wrap is essential for creating a healthy and comfortable home. Some wraps allow moisture to pass out without allowing external environmental factors (i.e. temperature) to pass inside. Others are basic in their design which only stop external temperatures entering your home.

To take building wraps to the next level, using Passive Home techniques will ensure your home is mould free and comfortable all year round.

Passive Homes rely heavily on advanced building techniques and materials to achieve high levels of energy efficiency and comfort. One critical component in this construction is the use of high-performance building wraps. These materials serve to enhance the thermal performance of a passive house, prevent moisture intrusion, and maintain airtightness.

How does a vapour barrier work?

Consider how food is stored for freshness like chips in a foil chip packet. Vapour barriers are sometimes used to prevent building assemblies from getting wet but they often prevent them from also drying out which can be very dangerous.

Back to the chip packet analogy, imagine if you have a sealed chip packet with crunchy dry chips but someone has added a dropper through the seal which drops in water every now and then (this is your bathroom steam, and moisture from people etc.). You’re going to have soggy chips in no time at all. Standard building principles rely on the packet not being sealed (coming in from your roof) so your chips don’t get soggy. But the chips at the bottom will always be soggy because air flow is not possible throughout the entire bag and the bag itself doesn’t allow water to leave. These soggy chips are a haven for mould and consuming these would make you very unwell.

Higher classed membranes will allow moisture to leave the chip packet despite being sealed and the dropper still dropping in water. Your chips at the bottom will no longer go soggy and mouldy.

How are wall wraps classified?

In Australia, wall wraps are categorized by their vapour control membrane (VCM) class, which depends on their vapour permeability. The classes are numbered 1 through to 4. 

Class 1 and 2

• These classes are classified as vapour barriers and are not vapour permeable. (Meaning they do not allow water in and do not allow water out)

• In hot and tropical climate zones, a vapour barrier should be completely taped and sealed. 

Class 3

• This class is classified as vapour permeable. (Allows water to move out and doesn’t allow water in)

• In external wall construction in Climate Zones 4–5, a Class 3 Vapour Permeable Membrane is required as a minimum. 

Class 4

• This class is more vapour permeable than Class 3. (allows more moisture out and still stops water from entering).

At WHC our standard practice for non-passive homes is using Proclima Solitex Extasa.

This is a vapour permeable membrane. It is also a WRB (weather resistant barrier) It essentially stops water coming into the dwelling but allows water vapour to leave.

Most standard builders, especially in Mildura are not using a vapour barrier. They use only a WRB which keeps moisture both out and in, class 1 or 2 wraps.

Being classed in a Zone 4 climate we are required to use class 3 per building codes, however both brands we use as standard such as Hardie wrap and Proclima are class 4 so therefore we are exceeding requirements as our standard practice.

In the below video, Jordan describes two examples of wall wraps and why we choose to use the Proclima Australia wrap as standard for our homes.

Passive Home Membranes

To take wraps and membrane further in their uses for passive home requirements, this does not include the standard practices above. Here is a list of the different types of passive home membranes (different to their classes (see above)) and their benefits.

·      Weather-Resistant Barriers (WRBs)

o   WRBs are designed to provide a shield against moisture and wind while still allowing walls to breathe.

·      Airtightness Barriers

o   These wraps are crucial for maintaining the stringent airtightness standards required for passive homes.

·      Insulating Wraps

o   These have integrated insulation properties, adding an extra layer of thermal protection.

·      Roof and Floor-Specific Wraps

o   Target specific areas to improve functionality and efficiency.

In Passive home construction membrane types can be either for one of or for multiple of the above uses.

Choosing the right passive home wrap depends on several factors, including climate, building design, and specific passive house goals. The wrap systems contribute significantly to the home’s overall performance, making the selection process an integral part of passive house construction. When implemented effectively, these wraps provide increased energy savings, comfort, and durability for years to come. As always, consultation with an experienced passive house designer or builder is recommended to tailor the wrap solution to the specific project needs.

At WHC we pride ourselves being the leading in the industry in Mildura. We are your Passive home builder in the Sunraysia district.

Book a consultation with us to discuss how passive home principles could benefit you and your family.