There’s a tropical elephant in the room.

As I commute to work daily, I continue to see multi-unit apartments being built with single skin masonry construction. I ask myself how this is even still possible today in light of the Building Code of Australia’s energy efficiency requirements.

As a NatHERS assessor and having been on the ABCB Technical Committee for Section 3.12 of the BCA, I know the unfortunate answer: politics. That and the great, largely unquestioned ‘truth’ about tropical design being bought by all and sundry involved in the process, that “tropical climate design doesn’t need wall insulation, it needs shade and plenty of ventilation.”

While passive design has improved our energy efficiency, we now have to move on. The reason we have as a design profession advocated passive responses to climate was to try to protect the planet from climate change. Since the early 1970s, some people have been aware that air conditioning was a climate issue. Well-intentioned designers such as University of QLD professors Dr Steve Szokolay and Bal Saini, the Sub-tropical Design Centre and many others like them – including certain QLD government policies – have advocated purely passive principles.

This quote from the Subtropical Design in South East Queensland policy from the SEQ Regional Plan demonstrates the thinking at work:

“So benign is the climate in subtropical South East Queensland (SEQ) that the natural conditions allow comfortable outdoor living all year round. The environmental temperature only slips outside the comfort zone on the coldest of winter mornings and on some sweltering summer days when heat and humidity combine. SEQ experiences neither searing nor freezing temperatures that other population centres in Australia and overseas routinely contend with. In theory, this means that in SEQ the need to artificially cool or heat habitable spaces is much less pressing than it is elsewhere.”

Unfortunately, given the vast majority of today’s societal comfort expectations, this line of thinking has become outmoded, and is now peddled as a half truth that largely ignores the fact that most houses today are air conditioned, not climatically free flowing well ventilated tropical houses.

People drive to work in air conditioned cars, they arrive to air conditioned work places, they go for lunch in air conditioned cafes and when they get home, they go straight in and switch the air conditioning on if it isn’t already on. People have acclimatised to air conditioning, they expect it, and our rising summer peak energy loads prove it. Society has moved on from passive design because politics and industry lobbyists prevented it from being able to deliver its full potential.

The fact that this Queensland policy and other tropical and sub-tropical design strategies have convinced themselves that “lightweight, low insulation, well shaded and ventilated home design” is the defining character that is required for comfort in today’s hot humid areas just shows how successful the building industry lobbyists and tropical design purists have been in keeping sensible, hybrid social behaviour and climatically aware design supressed.

Even Steve Szokolay’s well-founded and oft espoused message that effective wall and window insulation is needed in southeast Queensland in winter has been largely ignored and drowned by the ‘uneconomic returns’ arguments of the lobbyists and economic rationalists. The public outcry about skyrocketing energy costs is partially a symptom of failed building design and policy.

It’s not that that these design strategies are not appropriate passive responses to hot humid climates. They are, but the lack of success in getting the NatHERS building envelope standards up to a significant level (NatHERS Six Stars is still inadequate) means that new houses are still very uncomfortable in summer and completely ignores the fact that most people expect air conditioning installed from new or will install it after the very first summer.

The very fact that air conditioning is installed effectively changes the climate zone from hot humid to cold temperate, except the cold is on the inside in summer not outside in winter. When you look at the temperature differentials between the inside and the outside for Melbourne in winter versus air conditioned buildings in Queensland in the summer, they are of the same magnitude, except reversed!

I am not suggesting the same design solutions that works in Melbourne should be imported into tropical and sub-tropical design. However, we need to have more finessed design – a hybrid design solution where air conditioned spaces are required to have highly insulated walls, ceilings and windows. Spaces, especially living spaces, can be opened up and ventilation paths should be well designed so that when appropriate, they can be set up as climatically free flowing. When the humidity gets to a point where nothing is comfortable any more and even the ceiling fans aren’t working, that should be when you turn the air conditioning on. At that point, you close up the house and put effectively designed insulated barriers into place.

The design solution to the ‘elephant in the tropical design room’ is not a cold climate versus hot climate design solution. It’s not one or the other; it’s both. Hybrid design is the solution – designs that can climatically ‘swing both ways’ are needed.

The ABCB needs to get past the mantra of the past and deal with the realities of today: neither approach works on its own in the tropics. If we are to tackle the massive problem of incredibly imminent climate tipping points in the context of skyrocketing air conditioning use, we need to ratchet up the appropriate climate response: we need to wind back air conditioning, and we need a hybrid design solution if energy use is not to continue soaring.

  • Passive house is a good option. Insulation + airtightness + ventilation with good design will work well anywhere.

  • Interesting insight, thank you David Baggs. Another benefit of true Passive House Standard buildings is the ability to control humidity. Often if you can reduce humidity you can bear the higher temperatures much more easily, without needing aircon. With an air ventilation system as used in passive house standard buildings, you will have a nice air movement inside too! Fiona

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