Engineering Training Institute Australia (ETIA) Director, Paul Uno reflects on the evolution of curtain wall systems in Australia, from early brick façades to today’s high-performance glazing.
The term ‘Curtain Wall’ may be unfamiliar to some engineers in the marketplace. It is an expression that was coined many years ago to represent the glazing and metal framing that provides a lightweight façade to high rise structures.
When we look at high rise buildings and apartment towers in Australia today, we take for granted that the façade will primarily be glazing supported by aluminium sections. However, this system of façade construction has only been in the Australian marketplace since the late 1950s. Prior to this, buildings were not excessively high (usually less than 12 storeys) and thus heavy brick masonry was a very common façade in low to mid rise construction.
This system took off in major Australian capital cities in a big way in the 1980s when an American company called Cupples and H.H.Robertson (named after Harold Hansard Robertson, a Canadian American industrialist) started producing curtain wall panels in Australia.
I was fortunate enough to have worked for HHR-Cupples at the time the transformation took place. I was also appointed the structural curtain wall engineer, as well as the NATA (National Association of Testing Authorities) signatory, for the façade test rig on site.
Codes and testing
Testing of façade panels today is not carried out in Australia to the degree it used to be. The HHR curtain wall test rig that I oversaw was the largest in the southern hemisphere at the time (being 11 metres high x 9 metres wide x 2 metres deep). We were able to perform wind pressure tests on test façades to pressures of 10 kilopascals (kPa), water penetration tests, as well as air permeability and deflection tests.
The highest profile project I worked on at the time, in 1984, was the State Bank in Martin Place, Sydney. Until recently, this site was the location of the Channel 7 studios. Having visited this site recently, I was impressed to see how modern and classy the building still looks after 40 years.
One distinctive aspect of that project (as with most projects during those years) was the fact that all the glass, aluminium and granite stone panelling was manufactured or came from Australia, nothing was imported in those days.
We designed the aluminium sections to Australian Standard AS1664 and the glazing panels to AS1288, both of which still exist today, albeit in Limit State format. In fact, AS1288 was revised in 2021 to reflect new research done in this area.
The Aluminium Standard AS1664 was, and still is, heavily based on the American Aluminum Association guide called ‘Aluminum Design Manual’ or ADM (2020). A new version of ADM is due to be released in 2026.
Wind pressures
The wind pressures (and wind velocities) we used to test the Martin Plaza building were derived by Dr Bill Melbourne, who was based in Melbourne coincidentally.
He provided us with wind pressures applicable to this site and building profile (which were less than the conservative velocities that would have been obtained using the Wind Standard at the time, i.e. AS1170.2 1983).
Most engineers involved in wind design know that the greatest wind pressures are found on the corners of buildings where local effects produce suctions often two to three times higher than pressures elsewhere on the façade.
This building was designed to withstand wind pressures in the order of 2.2kPa and was proof tested accordingly in the 11-metre-high test rig at Chipping Norton, New South Wales.
Acoustic requirements
Another building I worked on was the ABC studios in Ultimo, Sydney, New South Wales. The glazing for this project relied heavily on reducing the sound transmission from external sources.
The specification called for STC (or Sound Transmission Class, a numerical rating that measures how effectively building materials and assemblies airborne sound transmission) values in some areas in the order of 37. Considering that a 100 millimetre (mm) concrete panel achieves an STL (Sound Transmission Loss) of around 44, it could be expected that achieving a loss of 37 decibels (dB) for glass would have required a relatively thick panel.
As it turned out, some of the options considered for this job was a composite single panel system comprising 6 LAM (laminated) / 6 Mono / 6 LAM, where the poly-vinyl-butyral interlayer (PVB) in both laminate panels was 1.14 millimetres in thickness, and which would have achieved an STC of around 39 dB.
One alternative was a double-glazed system comprising 5mm mono / 50mm air gap / 10mm mono (total thickness of 65mm and total mass of 32 kilograms per square metre) which would have achieved an STC of 41.
It requires some fairly thick (and heavy) glass panels to provide enough mass to minimise sound transmission across the glazing section.
Today the acoustic ratings are in terms of Rtw + Ctr, where Rtw is the Weighted Sound Reduction Index and Ctr is the spectrum adaptation term for traffic noise. It tells engineers how well the glass reduces everyday city noise, not just laboratory-style sound frequencies.
Rw + Ctr is generally more representative of actual urban performance expectations, compared to older measures such as STC, especially for façades along roads and airports.
The other significant glazing project I was involved with was sizing the glass and RHS (Rectangular Hollow Section) steel sections for the skylights on Parliament House in 1985. The primary aspect of this job was structural design to resist dead loads, live loads and wind actions.
Dead loads are the permanent, constant weights of the building components themselves, whereas live loads are temporary or variable loads, anything that can change over time or during use. Wind actions refer to the pressures and suction forces created by wind on the building envelope.
Thermal efficiency
The other important aspect of any curtain wall design (besides structural and acoustic requirements) is thermal efficiency, i.e. keeping heat out or in, depending upon the geographical location and the Building Codes/Standards that apply.
When I received the curtain wall specification for the Sydney Airport Centre in the 1980s, it nominated a transmission coefficient (or U value) of 6.4 watts per square metre per Kelvin and a visible light reflectance less than 20 per cent.
These days the technical requirements for glazing are much more detailed and more stringent than 30 years ago. Solar Heat Gain Coefficient (SHGC) is a more commonly quoted value that is required to be satisfied by a glazing system.
How you can learn more?
Engineers who do not have expertise in these aspects of curtain wall design can attend a two-day Glass and Aluminium Façade Design Workshop conducted at the Engineering Training Institute Australia (ETIA).
The next course will be livestreamed on Tuesday 11 and Wednesday 12 August 2026.
For more information, visit etia.net.au
