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Question

I was wondering if you could provide me with any information surrounding fixing details for timber frame work in cyclonic areas in Western Australia.

Woodsolutions Answer +

The reference for timber framed construction in cyclonic areas is Australian Standard 1684, Residential timber-framed construction, Part 3: Cyclonic areas. You can obtain a copy of AS 1684.3 from Standards Australia.

AS 1684.3, cyclone, cyclonic areas, WA
Question

We have specified the use of western red cedar in an office building to be used as either wall and/or ceiling cladding. Our BCA consultant requires confirmation that the western red cedar is a group 3 product as part of the BCA 1.10 clause.
If any timber makes it into group 3 in accordance with the BCA's Specification C1.10a, it doesn't matter what the shape of it is. Is that correct?

Woodsolutions Answer +

The Australian Timber Database at www.timber.net.au advises that western red cedar is a Group 3 material in accordance with the BCA's Specification C1.10a. The Database is maintained by the Timber Development Association of NSW. For further information contact TDA on (02) 8424 3700.

Our understanding is that the group number could be applied to a similar configuration, e.g. if 12mm western red cedar panelling is a Group 3 Material it would be reasonable to say that other flat panels of the same or greater thickness would also achieve Group 3 status.

However, the material's group number is an indication of its time to "flashover", as predicted by the heat release rate when exposed to a standard heat source. Consequently if you were designing a screen made up of thin battens of western red cedar with spaces between, it would be likely to have a more rapid heat release rate than a 12mm thick flat panel. Other configurations are likely to have greater or lesser rates of heat release. So we can't say that western red cedar is a Group 3 material in all cases.

BCA's Specification C1.10a, Group 3 materials, western red cedar, WRC, interior lining, flashover
Question

Does AS1684 specify that all roof and ceiling structures have to be built with H2 treated structural pine? The house specs are stating that the "Roof & Ceiling structure - Timber Frames to AS.1684 but we've been charged again in the site works page.

Woodsolutions Answer +

There is no requirement in AS 1684 for houses to be built with T2 treated pine. AS 1684 simply says "Protection against termites shall be provided in accordance with the provisions of the Building Code of Australia".

There are various ways of protecting new houses against termites, and using treated framing is only one of them. Other systems include chemical sprays and/or physical barriers.

In fact, even if treated framing is used we still recommend the installation of physical barriers since there are other items inside the home that termites can attack besides the wall and roof framing.

Treated framing is essentially a second line of defence in case the physical barriers are breached. Having said that, we consider treated framing is a good investment considering the relatively small extra cost.

termites, AS1684, T2, T2 treated pine, termite barriers
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