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Question

I’m an architect in Tasmania, and we have proposed using either blackbutt or spotted gum external cladding. Our client has asked what the life expectancy is of these timbers? We are thinking of leaving the boards raw, to silver off. A roof overhang of 450mm will be on all sides. I was hoping you might be able to give some advice on how we answer this question.

Woodsolutions Answer +

The best way to advise your client is by reference to Australian Standard 5604, Timber – Natural durability ratings. Blackbutt and spotted gum are both rated Class 1 durability outdoors, out of ground contact. According to AS 5604 this gives both timbers a probable life expectancy of greater than 40 years in situations ‘subject to periodic moderate wetting when ventilation and drainage are adequate’. That means avoiding water traps in joints and allowing rain to run off freely. Garden beds at the base of the wall should be avoided if they are likely to keep the wood damp. It might be helpful to refer to our Technical Guide no. 13 Finishing Timber Externally. Section 3.3.2 of the Guide has guidelines on the weathering of timber cladding. Note particularly the implications of splash-back at the base of the wall in Fig. 10. This can be avoided by constructing the base of the wall with an upstand of several courses of brickwork. Technical Design Guides can be downloaded from our website here: https://www.woodsolutions.com.au/articles/technical-design-guides.

Question

We are working on a project in which we require a 200x100mm post for a shop front. it goes flush against a tilled wall. It is is in a shop front location which has a 3 m awning and will sometimes get sun exposure.The post is non structural and are there for only decorative purpose in walnut finish. can you recommend what timber to use for this purpose. we can stain it walnut color if required.

Woodsolutions Answer +

That is a big post and could be difficult to obtain. You might have to look for recycled timber, maybe from an old bridge or wharf. Otherwise, glued laminated timber can be obtained in large sizes. If you write ‘glued laminated timber’ or the short term ‘glulam’ in your browser you will find the names of suppliers.

Question

I'm specifying a project that's in a BAL 12.5 zone. I'm hoping to achieve a look similar to the first image on this web page: https://www.everisttimber.com.au/cedar-cladding
but with the timbers approved for use in this zone. Please could you help by letting me know how to specify this colour mix and grain type and the most similar timber that would suit?

Woodsolutions Answer +

The timber in the Everist image is western red cedar as you probably know. BAL-12.5 is rated a Low Risk area and there are no restrictions on external wall surfaces 400mm or more from the ground. Cedar would be acceptable as long as some other material is used in the zone below 400mm. Sometimes the bottom of the wall is clad with several courses of brickwork, an attractive look that complies with the bushfire regs and prevents water staining from rain splashing at the base of the wall. Other materials that can be used at the base include 6mm fibre cement, bushfire-resisting timber, or any timber with a density of 750 kg/m³ or greater. Timbers with a density of 750 kg/m³ or greater will all be hardwoods.

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