The cliff-hanger at the end of last week's episode was the rupture between scientists and architects over thermal comfort in a house. At the centre of the argument is a computer program called NatHERS.

A quick recap. When the building code introduced energy efficiency standards for thermal comfort in houses 17 years ago, they used a computer program developed by scientists at the CSIRO, called NatHERS. It has a simulation engine called ‘Cheenath’ that could accurately predict internal temperatures aga inst real weather patterns, taken in 23 sites around Australia.

The regulators turned it upside down; instead of showing the internal temperatures, it now measured the energy used to achieve a pre-determined level of comfort. This involved a host of assumptions about the house: how many people in it; how they use it; when they open and close doors and windows; when they turn the air conditioning on and what temperature they want.

Individuality versus standardisation

Architects disputed the settings, but then went further: they refuted the very premise of using air conditioning, even if it was virtual. For them AC is the plutonium of architecture. They believe houses can be designed without AC and achieve thermal comfort, but the big question is: “what level of comfort?” For architects it was an irrelevant idea in the face of the connection to the environment in their highly glazed and openable houses.

All scientific evidence of NatHERS says the contrary. It may be ‘natural’, be it doesn’t naturally meet any reasonable comfort levels. NatHERS shows these houses overheat in summer and are too cold in winter against the program’s defined thermal comfort bands, the ‘standards’. But that may not a concern to architects, who argue it infringes their design freedom to make an interactive house, or to their clients who may enjoy operating the house in response to the surrounding environment and weather.

Scientists like caves; Architects like treehouses

If thermal comfort is a key aim in designing a house, then the cave is a good model. Insulated all the way round, high thermal mass to provide a steady internal temperature, minimum openings, minimum air change, and accentuation of keeping warm in winter in particular architects.

If connection to the environment is the aim, then head to the treehouse. Light and airy, lots of views into the connected landscape space dissolved through opening glazed doors, framed by treelike post and beams. Too live at one with the environment, you adapt to it.

The cave is the default position for the majority of Australian housing, a solid box made with selected openings punctuated into the walls, a glazing ratio (of glass to floor area) somewhere between 15 and 25 percent. The European vernacular of a thousand years and Adolf Loos’ ‘Raumplan’

The treehouse is the designed the opposite way: open frames where the choice is where to ‘wall’ it up; and the glazing ratio is 50 to 60 percent. The Asian tradition, Farnsworth, and Le Corbusier’s ‘Plan Libre’.

The ’Esky’ vs the Tent

By far the majority of our houses have relatively low glazing ratios. Project homes are designed with modest amounts of windows and doors because they are the most expensive elements. And NatHERS seeks to make them into a better ‘Esky’: insulation in the walls and roofs; restricted glazing as the ‘thermal wound in the envelope skin’; the most propitious orientations to winter sun, and away from the summer heat; thermal mass and minimum air changes; and no project home these days is sold without some form of AC package.

The occupants are happy to have a sealed-up house, giving acoustic and visual privacy, with AC for dialled-up comfort. NatHERS works well on these ‘Eskies’ and caves, the virtual air conditioner spits out a high score and approval for such a house, giving them a high number of stars. The scientists are on the side of the 95 percent.

On the other hand, some architects want the opposite: the well-heeled tent to enjoy being close to nature and environment. High glazing ratios capable of maximum interaction with its surroundings; multi-stacking or bi-fold glass opening from the inside to the outside. Architects intuitively believe that the house is comfortable because it can be infinitely adjusted for comfort.

Occupants of these ‘tents’ accommodate the higher temperatures in summer because the doors are open and they're in/outside. Extra layers of clothes keep them warm to compensate for the cold in winter. NatHERS struggles here: no amount of high-performance glazing can bring it down to a level where AC can be energy efficient. The house can never achieve the levels of thermal comfort in an air-conditioned cave, not without extraordinarily excessive energy use.

Resolving the culture clash.

Last week I promised to try and square the circle. Architecture and Science. I am reminded of Henry Cowan, inaugural professor the Department of Architectural Science at The University Sydney who thought those two words oxymoronic and called his autobiography A Contradiction In Terms. Nevertheless, I think there are three ways forward.

Hybrid Houses in NatHERS

Scientists need a way to measure ‘hybrid’ houses in NatHERS. Many architects’ houses are brilliant in Spring and Autumn without AC, the house being turned into some form of extended veranda. And this part of the house should be exempt from NatHERS if no AC other than ceiling fans is fitted. If these areas are modelled in NatHERS for temperature, as originally intended, the scientists will see their value in the changeover seasons.

But architects will have to accept that a part of the house will have to meet NatHERS standards (and thus fitted with AC), at least as insurance against global warming. The house has the best of both worlds.

Change NatHERS into simpler regulations.

Alternatively, we could have simpler, but very stringent, regulations with insulation or resistance values for each part of the house, as in Section J for other building classes. The whole roof might have to reach a value of, say 4, and each wall, all the solid and glazed elements, might have to reach a standard of say 1.5. Only achievable if the glazing is reduced in area, or much higher performance than is currently used.

The designs are flexible, and the architect designed house is possible, but not without raising the quality of the framing and the performance of the glazing, to meet a higher overall standard. The key here is to simplify the science so architects can understand it: no black box, but rather numerical values for the parts and elements of design that architects understand. It may cause architects to reflect on whether glazing ratios of 60 percent are still viable at the increased performance cost, or maybe 30 percent will do at half the cost.

No NatHERS, just bigger bills

If energy efficiency is the main aim, I would radically change energy costs. Equity would come from a stepped energy bill: a small amount is free, and then each block of energy gets exponentially more expensive.

Let’s assume that 33 percent of the average bill has no charge. A baseline of energy is supplied free to everybody, like a universal wage. The socially waged, the frugal, the careful can run a house very effectively without cost. Above that charges are levied, say the next 33 percent costs the total of the current average bill, an incentive to save. And then the charges increase dramatically. Above the average energy amount, the energy price doubles, and then quadruples.

The increasing costs encourage something to be done about the existing poorly designed houses, and to improve new ones. There is an incentive to either improve the thermal performance or install photovoltaics cells. Either way, the intention is to show the importance of energy efficiency, as well as air quality and thermal comfort.

Climate Change and Covid-19

An improved NatHERS is beautifully placed to address the two big issues of our times: climate change and Covid-19. Increasingly, trapped in our homes, we want to be comfortable, but we need to reduce our energy use, to lower CO₂. Maybe the time is right to revisit NatHERS, to build a hybrid model, to make it more accessible to science-averse architects, and to change our energy billing. Time to improve our 8 million existing homes, and the 220,000 we build each year.

Tone Wheeler is principal architect at Environa Studio, Adjunct Professor at UNSW and is President of the Australian Architecture Association. Please note that I do not read Instagram, Facebook, Twitter or Linked In. My sanity is preserved by replying only to comments addressed to toneontuesday@gmail.com. The views expressed here are solely those of the author and are not held or endorsed by A+D, the AAA or UNSW.

Tone Wheeler

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