WRAP IT RIGHT: Perforated foils with fibre cement cladding, a thing of the past

There is a common misconception in the marketplace concerning the use of a ‘breathable wall wrap’ behind fibre cement cladding. It is generally assumed that fixing a perforated wall wrap in this application is the sure safe way to guarantee the system complies with its specification requirements. However, is the Vapour Barrier classification the only important material property to consider? 

It is important that installers are aware of the various requirements building product manufacturer’s stipulate when selecting the correct wall wrap for use in a system. James Hardie for example state the following with regards to selecting the correct wall wrap for use behind their external cladding:

“…the designer must ensure that the product is fit for purpose and has the following properties in accordance with AS/NZS 4200.1:

• Vapour Barrier - Low or Medium
• Water Barrier – High”

However, in hot, humid regions (Climate Zone 1 as defined by the ABCB), it may be more suitable to use a wall wrap which possesses the following material properties in accordance with AS/NZS 4200.1 (always check with the designer):

• Vapour Barrier - High
• Water Barrier – High

With this in mind, the use of perforated wall wraps behind products such as Scyon™ Linea™ weatherboard in either scenario could be unsuitable.  For instance Sisalation^® Wallwrap MD Breather possesses the following material properties:

• Vapour Barrier - Low
• Water Barrier – Unclassified

So what does ‘unclassified’ mean?

The water barrier classification of a product is generally determined in accordance with AS4201.2. This particular test method involves securing a test membrane to the base of a cylinder and then filling that cylinder with 100mm of coloured water.  After waiting for a period of 24 hours, filter paper, laid beneath the suspended test specimen, is inspected for staining. If there is no staining present, the specimen passes and is assigned a ‘high’ water barrier classification. If staining is present, the specimen does not pass and is therefore deemed ‘unclassified’.

Based on this information, Fletcher Insulation recommends that the cladding manufacturer’s installation guidelines are referred to for the most up-to-date, relevant information.

As a general note, perforated wall wraps are likely to be incompatible with fibre cement construction. Fletcher Insulation recommends the following membranes for a fibre cement system with regard to various Climate Zones:

Unsure of the climate zone your building is situated in?

This may be determined by referencing a current ABCB Climate Zone map. Alternatively, you can refer to Fletcher Insulation’s FletcherSpec™ Pro application. This newly released app contains an in-built climate zone tool which determines your climate zone based on the postcode and local government area provided. The program is also able to outline your minimum insulation requirements as well as the Total R-value of a system in accordance with the Deemed to Satisfy Provisions of the National Construction Code.

© Fletcher Insulation Pty Limited 2015. Fletcher Insulation reserves the right to change product specifications without prior notification. Information in this publication and otherwise supplied to users as to the subject product is based on our general experience and is given in good faith, but because of the many particular factors which are outside our knowledge and control and affect the use of products, no warranty is given or is to be implied with respect to either such information or the product itself, in particular the suitability of the product for any particular purpose. The purchaser should independently determine the suitability of the product for the intended application. Scyon™ and Linea™ are trademarks owned by James Hardie Technology Limited. Tyvek^® is a trademark of E.I. du Pont de Nemors and Company. All other ™ and ® are trademarks and registered trademarks of Fletcher Insulation Pty Limited ABN 72 001 175 355.