Today, most Australian design teams will have experienced the post-2010 industry shift from using the BCA Section J calculators to assessing the façade design ‘allowance for glazing’ by adopting the JV3 alternative energy modelling pathway.

Through this alternative pathway, we have become accustomed to a more flexible approach of ‘trading off’ performance elements of the envelope to ‘outperform’ a theoretical reference design. While this has brought some freedom to designs, in particular more glass (by area), it carries a very large caveat; the reference design that we are trying to outperform is, to be frank, absolute (theoretical) rubbish.

The reference design is made up of NCC (BCA) default values for all building services and building fabric components (all good) except for the glazing systems (not so good). In the case of glazing, a consultant or engineer will often generate the absolute worst performing glazing based on the designs required window to wall ratio. This makes 100 per cent sense, as their duty is to the client in order to make the design ‘work.’

For example, if 40 per cent of a façade is designed as vision area and the rest made up of various opaque elements (spandrels, composite finishes, standard brick walls, and so on), the industry’s informal protocol is to tweak glazing performance values (Total SHGC [solar control] and U-values [conductance]) to generate a relic of glass thermal performance more common in the 1970s than in 2015.

For example, in the case below for Melbourne, a 50 per cent window-to-wall ratio means that our reference building glazing has Total SHGC and U-values of 0.28 to 0.33 (depending on orientation) and 5.5 watts per metre squared Kelvin (W/m2K) respectively.

To the uninitiated, this typical tale means dark glass on north, east and west façades and highly transparent glass (SHGC 0.80) to the south, while we can freely throw in some single glazing options to round off this disconnection with modern design.

Are we really suggesting that our reference of good design is so unambitious?

Could following this trend not directly facilitate an ever increasing gap between the global building stock and the structures we are building today?

Today’s ‘generation’ of performance requirements for the reference design are completely at odds with other advanced building markets and indicative of a need for greater discussion around how we set the minimum performance of our future building stock.

Without any real responsibility or system to ensure we are using a common method (such as the accreditation body ABSA on the residential side of compliance modelling), commercial modelling is arguably unaudited and has no governing body to bring those undertaking the modelling into line.

In Shanghai, if we use the local energy design standard (DGJ08) as we would in Australia for our reference design, the performance values would be set as a function of our window to wall ratio. Meaning, if we have 50 per cent WWR, then SHGC and U-values are non-negotiable. This makes sense if we want an easy to identify reference that is indicative of modern building performance.

Moving further south, in Hong Kong, Jakarta or Singapore, the amount of heat transfer is directly limited via thermal transfer calculations (OTTV, ETTV, RTTV), creating an onus on the design process to ensure performance glazing is specified and purposeful shading devices are designed for.

The same would apply if you opted for the American/International standard, ASHRAE 90.1 (the most commonly adopted reference design standard for performance). There are no magic tricks to set a reference design; a standard sets the values you must use. The UK is not exactly the same, but it is analogous.

We are already struggling to surpass this watered down reference design in many of today’s design teams. If we were to adopt international standards, most of our buildings would be forever stuck in the planning cycle, never to be realised.

What we need is a more unified (a single calculation engine) and challenging (mandatory air-tightness) approach to setting higher minimum façade performance within our buildings. Otherwise those that are going up around us will simply stand as testaments to our design and construct shortcomings and lack of foresight.

  • Thank you Darren for this article.

    Wondering why more people don't use the Passive House Planning Package in designing facade systems? Combined with proper auditing and testing during and after construction, there is no room to fudge the figures. You get proper results as to performance of the buildings with respect to energy consumption.

    Oh, and you also get the most comfortable indoor ambient temperatures, and the healthiest air, and no condensation and mould, and very very low energy consumption for the operators/occupiers.

    They are starting to show in Europe that high rise passive house buildings can be on a par cost wise in terms of construction. Much less plant required. So why aren't more people going this way – regardless of all the inferior codes around?


    • Fiona,

      You don't need to sell it to me!

      Its comes down to the $$$ and the industry is just waking up to the value of low infiltration design.

      The good news is that i am across a couple of government projects where better facades are a very strong point of focus, so we are seeing some positive steps.



  • 50% WWR? More like 70-90% WWR and sometimes 100% WWR! The architectural intent is always the transparent, fully glazed box, all the more to see in, to visually connect the building occupants to outdoors, etc., etc., etc. At this type of WWR, the glazing calculators churn out quite onerous glazing performance requirements. Even with glazing calculators driving the Reference Design, the typical Proposed Design glazing solution is the application of highly selective triple low-e/silver double glazing products that achieve mid-pane U-values of around 1.6-1.8 W/sq.m.K and an SHGC of less than 0.3. This is top-of-the-range glazing tech. And this type of solution is applied even with passive solar shading measures to ensure perimeter peak zone loads are managed within the context of the HVAC system.

    Whenever it comes to facade design, the architectural, acoustic and thermal drivers typically result in a high performance glazing solution. And generally the project budget allows for this. We're even starting to see closed cavity facade solutions.

    • Fair points Alan,

      The issue remains that selecting lower WWR allows easier trade-off that resemble very low aspirations and this system is deeply flawed.

      Yes, to make the case for higher WWR, the trade-off gets more challenging dependent on your orientation, but the 'generation' of a reference 'allowance' for glazing allows individuals to play performance god in my view.

      For example, jumping to 70/80% still on the north for Melbourne/Sydney still allows individuals to choose a high conductivity and low for shgh, effectively fixing the result so winter losses are large and summer gains low. Flip this to the south and we are choose high shgc and low conductivity, creating a winter optimised solution.

      In terms of budget allowance, while center pane performance values are allowed/predicted, the inclusion of frames loss and the understanding of the resultant impact to the total performance value renders a so called 'high performance' solutions deeply in question in many of today's higher profile designs in my personal view.

  • This approach isn't limited to commercial buildings. The 'verification using a reference building' method for residential buildings will lower the benchmark for compliance in the same way a JV3 works. How do you think the glass boxes that feature in the glossy magazines get built – there is not way they would achieve a six star rating!

  • Darren,
    While many valid points are raised in your article, I don't think another box ticking exercise, be it in the form of 'a single calculation engine' is the right approach. As an industry we should be encouraging a focus on the design process. While I'm not a big fan of the glass box (with excessive layers of glass), I'm also not a fan of an esky with a few bits of glass. But the great thing about our industry is the freedom of design and while we need targets, the last thing we need is an increase design restrictions. The Alternative Solution process is there to allow for freedom of design, by establishing a thermal reference case that the design team need to better, so maybe it’s just the base line that needs to be lifted?

    • Patrick, when comparing our envelopes to those in economic hearts of Asia, Europe the Middle East and America, they don't stack up as being comparable from a performance point of view when adjusted for climatic variances.

      The Alternative Solution process allows freedom via creating poor benchmarks that allow freedom of design to the point of poor thermal performance (building typology dependent).

      Being on the front line of facade design (maybe 250 national and International projects in 3 years alone), we simply need to lift our game and produce facades that stack up. Sure, adjust the reference case but make it the same for all so the goals are clearer and we are more challenged. The JV3 approach is not challenging enough!

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