As the proposed changes to the NCC 2016 are currently up for debate, it’s undoubtedly worthwhile to dig a little bit deeper in terms of what this may mean for energy compliance of residential towers.

The ABCB has opened the floor for an alternative verification for multi-unit residential energy efficiency compliance. This new proposal is a rather large shake-up, particularly because:

  1. It allows modelling of the whole building, removing the requirement for individual apartment models
  2. This method moves away from the traditional commercial building verification process, and has a fixed comparison building

Focussing on the second point, the proposed modelling methodology requires that you simulate a hypothetical building (the ‘reference building’) which has fixed parameters for fabric thermal efficiency. Some of these exceed the current BCA minimum requirements (roofs and ground floor) and some fail to meet them (external walls).

There are two separate glazing definitions, depending on where your project is located; if you’re in Brisbane or Darwin for example, you have one window specification, whereas if you’re in Perth, Sydney, Melbourne or Hobart you have a different window specification. But fundamentally the whole country has been split into two climate zones, a massive change from the 69 that NatHERS uses.

The attraction of having a specified reference case is that you needn’t necessarily go through the process of modelling. If you simply meet the stipulated values, by default you would have a compliant solution. This simplifies compliance massively, and understandably is appealing.

But there is a massive flaw in the proposal: the reference case allows for poorly designed developments which certainly aren’t climate suitable. You could in theory put the same apartment tower, with the same fabric specifications, in Perth, Hobart, Melbourne and Sydney, and every one would comply. How does this make sense?

Residential apartments with a western orientation, 100 per cent window to wall ratio, no shading and glass with minimal solar load reduction would be compliant in Brisbane! From a comfort point of view, I certainly wouldn’t want to live anywhere like that, and I definitely couldn’t afford the energy bills.

Based on recent apartment tower layouts we’ve worked on, comparing how the reference case would fare in the NatHERS assessment is actually quite shocking. One apartment in Brisbane gets a score of 0 stars, meaning that the energy efficiency is not even recognised. Looking at Melbourne, a west-facing one-bedroom apartment achieves 2.6 stars, far below the current requirement of 5.


Overall across the board, none of the apartments I modelled would meet the current minimum NatHERS requirement. Surely we should be improving the energy performance of buildings in Australia, not worsening them!

I think if we’re setting window specifications for the reference building, we also need to set a hypothetical size of the window too, either via a window to wall ratio or a limit on the heating and cooling loads of the space. This would put a limit on the amount of solar radiation penetrating into the space and ensure that glass boxes would have sufficient shading or material specifications to suit.

Further work definitely needs to be carried out to investigate what impact this proposal would have on the industry. I would certainly be interested in seeing the ABCB’s analysis to date. But whilst compliance is driving design, which unfortunately in multi-residential towers it certainly is, we need to be pushing things forwards, not backwards.

  • It is crazy to think we are governed by specifications for insulation on refrigerant piping and chilled water piping to reduce losses within the building but the single biggest waste of energy through the facades and windows gets so little attention. Surely we can come up with a system which limits the requirement for air conditioning to all buildings through good Architectural design and not rely on costly AC

    • Todd I completely agree, there is so much focus on some areas, whilst completely disregarding others that are fundamental to sustainable design. My particular bugbears are air permeability and thermal bridging, and the lack of ensuring that what is specified is actually installed. We have a long way to go!

  • Agree we need to set limit on the size of the windows for the reference case building.

    I think a window area to floor area ratio is most sensible. Perhaps a limit of total glazed area equal to or less than 20-25% of floor area. And 15-20% if the dwelling is single sided. 10-15% if single sided and west facing?

    • Interesting points, we've certainly found that there is a large sensitivity in floor area to exposed area ratio. It's finding a balance between window area, access to daylight and occupants' well being that needs to be determined.

      The standards also need to be clear and concise, so that there is no manipulation of the results (as is often currently the case for JV3)

      One benefit of moving to a three-year code arrangement is that perhaps we can spend those three years researching the impact of code changes rather than rushing them through.

  • One of these days we will be "brave" enough to factor in the invested energy in making all that glass too…. or maybe not! I would love to know how, when recently I flew through about five climate zones on a flight to London and back, the "solution" to a facade on a new office block was ALWAYS glass curtain wall! And I have lost count of buildings in Australia that have "sun control devices" on their southern elevation.

    • Not only that, Sam, but if the thermal effects of all those aluminium framed spandrel panels were taken into consideration, we would perhaps have a different story!

      The architectural response is changing, certainly with the latest generation of architects who are more conscientious about the energy efficiency and indoor quality of a building. We do however unfortunately still fairly regularly come across jobs with unnecessary and over-the-top shading devices or glass that is far too dark for its orientation and usage.

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