Timber cladding is back. Using cedar timber cladding on buildings over 10 metres in height is now possible again thanks to Fireshield WoodSafe-Exterior. In 2017 a restriction on the use of combustible external claddings was published in the New Zealand Building Code (C: Protection from Fire: C/AS2) which meant that the maximum height for timber cladding was restricted to buildings under 10 metres in height.

Gone were all the inspirational designs utilising timber facades. With the introduction of WoodSafe-Exterior to NZ, with its Type A certification, architects can use Western Red Cedar in all forms of timber profiles, to once again bring beauty and design freedom back into our building industry.

Let's get technical:

WoodSafe-Exterior is an off-site fire retardant treatment applied to Western Red Cedar exterior cladding and provides a certified Type A fire rating.

All claddings for buildings over 10 metres in height require a fire test. The test is a small-scale cone calorimeter test to ISO 5660 that provides a total and peak heat release rate of the material. the higher the heat release rate, the more combustible the material.

The testing requirement applies to all components within the cladding system and as a result WoodSafe-Exterior cladding must be specified as part of a complete Type A system. The cladding system is defined as the outside or exterior weather-resistant surface of the building and this includes:

• Cladding
• Underlays
• Cavity components
• Windows and doors
• All penetrations, flashings, seals, joints and junctions

There are two types of categories for cladding material:

• Cladding Type–A: Peak heat release rate (kW/m2): 100 / Total heat release rate (MJ/m2): 25
• Cladding Type–B: Peak heat release rate (kW/m2): 150 / Total heat release rate (MJ/m2): 50

The Acceptable Solution allows for Type A external claddings to be installed where the building is over 10m in height, and/or where there is less than 1m from the boundary.

Timber claddings with fire retardant treatment are required to be pre-weathered in accordance with the ASTM2898 weather testing method prior to fire testing. This ensures durability of the fire-retardant properties.

The WoodSafe-Exterior system never has to be redone and provides the Type A certification for the lifespan of the timber. You can stain the timber in a wide range of compliant stains should you wish, however, from a fire perspective there is simply no maintenance required — it’s there for life.

WoodSafe-Exterior cedar is available from local suppliers such as Hermpac in four popular exterior profiles as well as fins and battens for exterior use. WoodSafe-Exterior also provides a Group 1-S surface rating and can be used in internal wet areas.

Should you wish to get back to nature and design in timber again, find out more from www.woodsafe.co.nz