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PostPosted: Mon Jan 23, 2012 12:25 pm
by clyde_anderson
I think you have your climate zones mixed up. The climate zones are ordered such that 1 is (roughly) the hottest & 8 is (roughly) the coldest. Cities that match each climate zone area are as follows:
1- Darwin, Cairns, Derby
2- Brisbane, Mackay, Coffs Harbour
3- Longreach, Alice Springs
4- Wagga Wagga, Dubbo, Coober Pedy, Kalgoorlie-Boulder
5- Sydney central, Adelaide, Perth
6- Melbourne, Mount Gambier, Albany
7- Canberra, Bathurst, Hobart
8- The peaks of the Snowy Mountains & the Central Plateau

In this respect, it makes sense that the insulation requirements for chilled water pipes are higher in climate zones 1, 2, 3 & 5 than in 4, 6, 7 & 8. This climate-specific insulation imbalance is reversed for heated water pipes (more insulation is needed in zones 4, 6, 7 & 8 than in zones 1, 2, 3 & 5).

Energy efficiency is one reason but preventing condensation is just as important. Condensation inside wall or ceiling cavities is a quick way to have a mould outbreak, causing respiratory problems inside the building plus rotting wooden supports. Preventing condensation within cavities is one of the reasons why at least 50% of a residential building's total roof/ceiling insulation must be installed on the ceiling, not the roof.


PostPosted: Mon Jan 23, 2012 3:38 pm
by JohnB
Thanks Clyde for your answer. I do agree with everything you have posted except maybe mixing up the zones.
I was referring in my original post to the Sydney metro area. In terms of climate zones, Sydney metro is divided into two zones: Zone 5 (generally areas closer to the shore including CBD) and zone 6 (generally areas further inland like Penrith as an example). Without the doubt the dry bulb temperatures in the inland suburbs are higher than closer to the ocean. The temperatures in Penrith (used as an example above) is several degrees higher than in CBD.
This is the reason for my confusion and the original post.
I wish I could attach the zone chart to illustrate the above but the file is too big and I guess you have it anyway.
Also, the confusing table in BCA is table 2a, Item 3 (c) in Specification J5.4 (page 540 in 2011 edition).
PS I value your comment more than any other contribution and would appreciate that this discussion continues until full clarification.


PostPosted: Mon Jan 23, 2012 5:01 pm
by clyde_anderson
Ah, then that's a question of climate zoning in general. The BCA climate zone boundaries were computed based upon weather data sourced from the Bureau of Meteorology. Eight different climates were isolated, designed to account for the overall differences in climate types (including temperature, humidity, wind speeds, solar irradiation, rainfall patterns, etc). The data was then mapped to council borders for simplicity. After that some political fiddling happened as per the whims of various councils, who for one reason or another wanted to be in a different climate zone. After all of this simplifying, the end result is something that's "good enough" without becoming too complicated. There's many anomalies & areas that don't make sense, but these are just unfortunately something that we have to live with as a trade-off of simplifying it to something manageable.

The AccuRate engine has simplified Australia's climate down to 69 zones. This was divided up at the post code boundaries, however many post codes can use more than one zone (are you on the East or West side of a hill? The bottom or the top? Direct beach front or a few blocks inland?). Even when broken up into such fine detail with all these choices, the differences in some areas are astounding. In Darlington a house may result in a calculated estimated total energy use of 70 MegaJoules per square metre whereas just over the road at the University of Sydney, the same house in the same orientation will result in a calculated 90 MegaJoules per square metre.

They rarely update the zoning borders, however you can always contact the ABCB to request clarification or submit a request for change! Their website is .

I guess the main point is that at the end of the day you should install the amount insulation that is appropriate for the situation, so long as it is above the minimum amount required by the BCA. The BCA is supposed to be considered as just the bare minimum, it is by no means meant to be a set of guidelines or a check list followed exactly to the letter. Its purpose is to forbid bad design, not to encourage good design!