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    Can we finally say goodbye to glass skyscrapers?

    McKenna Moroz

    London’s famous Crystal Palace may have been destroyed by fire in 1936 but its legacy lives on. The giant glass-and-iron landmark didn’t just set an architectural standard for exhibition halls that lasted centuries; it also deeply influenced the way we perceive buildings and their materiality today.

    Its structure – which comprised an intricate network of 1,000 slender iron beams and pillars, supporting 84,000sqm of transparent glass formed into the largest sheets ever made – provided a level of open floor space, natural light and transparency previously unseen in buildings of its size.

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    The Crystal Palace in London is credited with profoundly influencing the way we view, perceive and design buildings today

    As the first-ever, large-scale glass-and-metal building, the Crystal Palace was an architectural wonder. But more than that, it signalled a new era of architectural exploration; one aligned with a new, modernist optimism and equipped with all its most revolutionary technologies.

    The now-ubiquitous glass skyscraper is one of the results of this exploration of which the Crystal Palace was a pioneer. With thanks to modernist architects like Ludwig Mies Van Der Rohe and Skidmore, Owings & Merrill, our modern cities are literally filled with them.

    Like modernists within other fields, Van Der Rohe and other architects that worked within what came to be called the ‘International Style’ were deeply committed to the idea of ‘universal access’. In the case of architecture, this meant creating easily-emulated building templates that could be translated for use around the world.

    Guided by the mantra of ‘more with less’ – and harnessing the intrinsically modern social, financial and cultural associations of glass and steel – the Internationalists implemented a globalised model for glass skyscraper design. This building model went on to become aspirational for world economies everywhere.

    It is only now, from the vantage of our contemporary viewpoint, that we know how problematic this universal model could be. Specifically that these buildings – which generally resemble a glass-skinned box with a central services core – were built irrespective of the place they inhabited, for the sake of broader philosophical goals and symbolic meaning.

    POST-MODERNISM AND CLIMATE CHANGE

    Despite major advances in the environmental performance of glass skyscrapers over the past few decades, there is a growing consensus within the architecture and engineering industries that we cannot keep designing tall buildings with full-height glazing. Quite simply, it is not sustainable.

    In 2014, UK Architect Ken Shuttleworth famously denounced the design of London’s Gerkin building, which he had worked on while employed at Foster + Partners. Shuttleworth has since become one of the faces of the anti-glazed buildings movement in the UK. He has publicly said that he wouldn’t design the Gerkin the same way if he had his chance again.

    David Coley, also from the UK where he is professor of low carbon design at the University of Bath, shares Shuttleworth’s view. In an article he penned for The Conversation in 2015, Coley made the prediction that glass would become the major building material casualty of progressive sustainable architecture.

    His major reason for this was that glass is a poor insulator, and highly-glazed buildings require an unsustainable level of mechanical heating and/or cooling.

    “For decades glass has been everywhere, even in so-called ‘modern’ or ‘sustainable’ architecture such as London’s Gerkin,” he wrote. “However, in energy terms, glass is extremely inefficient – it does little but leak heat on cold winter nights and turn buildings into greenhouses on summer days.”

    Tellingly, the Crystal Palace of London was modelled off a greenhouse design. It was also designed by a landscaper. With this coincidence in mind, could it be possible that Coley and Shuttleworth have a point?

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    The Crystal Palace in London

    Put very simply, they do. A quick comparison of the insulating values of a high-performance clear glazing unit and an insulated wall grounds their position in fact. 

    However, it could be argued that Coley’s position is a little simplistic (if we are to give him the benefit of the doubt, this could be due to The Conversation’s restrictive word limit). Coincidentally, his argument also lends itself to the same type of universalism that became the ultimate downfall of modernism.

    Coley is right in saying that the U-value of triple glazing (around 1.0) is far worse than that of a well-insulated wall (nearing 0.1), but this is a singular analysis of one of the roles glass plays in a building’s entire energy performance. All considered, we should not be so quick to right-off its importance in sustainable design.

    For example, Dr. Philip Oldfield, a senior lecturer in high performance architecture at University of NSW, notes that a high amount of glazing (around 80%) on the north façade of a Melbourne tower could actually reduce the energy needs of the building when used with shading, since the additional solar heat gain would offset the cold winter temperatures.

    Coley also neglects to note that not all of a glass curtain wall’s function is as a window. Sustainability consultant Steve King explains:

    “Where optical transparency is not an issue, glass can be backed by extremely efficient insulation,” he says. “Such a wall can far outperform the heat transmission characteristics of traditional wall assemblies.”

    King also argues that a more comprehensive discussion of glass skyscrapers and sustainability would acknowledge that glass wall assemblies are easy to disassemble, recycle, repurpose and maintain. They are also excellent substrates for emerging thin film photovoltaics that can contribute to turning a building into a net energy exporter.

    ONE SIZE DOES NOT FIT ALL

    Oldfield is one of many within the industry who implores architects to curtail the use of glass on tall buildings. However, that’s not to say he advocates for its elimination from building design.

    “I’m not suggesting we need to lower the amount of glass everywhere – [we should] just be more careful with where and how we use [it],” he says. “The problem is [that] we’re using glass in the same way in every climate in Australia. We need to better respond to the unique [characteristics] of our different climates in façade design.”

    Alistair Grice, the commercial specification manager at Somfy Oceania, agrees with Oldfield – at least on the point that we should be taking a more site-based and year-round approach to façade modelling and design.

    As Grice points out, buildings and façades are often modelled on the worst solar heat gain scenario of the year. This means that static façades designed to mitigate solar heat gain around the calendar are actually doing a disservice to the building’s performance by wasting a valuable resource (the sun) in winter months, as this free energy could be used to passively warm the building.

    Somfy produces sophisticated Blind Control Systems (BCS), which operate according to both the sun’s positioning and a building’s internal temperature. This operation is tracked by a massive number of temperature, glare and weather station monitors.  The company was recently chosen to supply the automation solution for Australia’s first pressurised, closed-cavity façade with built-in timber venetian blinds at 200 George Street, Sydney.

    The envelope of the 37-storey tower contains approximately 16,000sqm of floor-to-ceiling moisture-maintenance free, sustainable, closed-cavity façade panels (M-free-SCCF), produced by architectural envelope specialists Permasteelisa Group. Fully-automated timber venetians sit within the cavities of the panels and are controlled (i.e. opened and closed) by a building-wide IP network designed by Somfy. This network in turn offers sun-tracking, shadow management and integrated, web-based remote controls.

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    200 George Street uses sophisticated Blind Control Systems (BCS) to moderate the building's internal temperature. Image: Mirvac

    The building’s façade is widely considered cutting-edge, as it provides a heat transfer coefficient of between 0,90 (blinds-down) and 1,20 (blinds-up) with ultra-clear, full-height glazing and without the loss of net-lettable-area associated with other double skin façade systems (DSF).

    As much as this innovation is energy-efficient, it is far from cost-efficient. Oldfield might suggest that the amount of money, effort and embodied energy that goes into the development of such sophisticated façade units could be better-served elsewhere. 

    Oldfield says that although these systems have been successful in improving the performance of glazed towers without impacting views out, they are also guilty of over-complicating an issue that could be overcome by simple and cost-effective design. For instance, with the use of shading or more solidity in a façade.

    It should be said, however, that Somfy and other suppliers also provide affordable and high-performing BCSs that can be used on all façade types, with varying glazing percentages to significant effect.

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    The envelope of the 37-storey tower contains approximatley 16,000sqm of floor-to-ceiling moisture-maintenance free, sustainable, closed-cavity facade panels (M-free-SCCF). Image: Mirvac

    THE BOUNDARIES OF TECHNOLOGY

    The technologies Oldfield broadly refers to include things like DSFs, advanced coatings and some more exotic ideas such as vacuum-glazing and adaptive biomimetic shading systems. All of these applications significantly reduce unwanted heat loss and heat gain for a building while safeguarding natural light and views.

    Alistair Guthrie, a fellow of Arup and one of the world’s most prolific skyscraper engineers, has experienced the evolution of glass technology first-hand. Clearly an advocate, Guthrie goes so far as to call it the most positive advancement in commercial tower design.

    “The sort of curtain walls that we now achieve - the size of glass, the selective coatings, the multiple glass layers with automatic blinds – [have] made a huge difference to both the performance of the façade as well as what it looks like.”

    Guthrie worked on The Shard tower in London alongside Pritzker architect Renzo Piano. He notes that intense material and product investigation were required to achieve the architect’s vision, as well as to ensure a high-level of energy efficiency.

    “The architect had a vision of this ‘shard of glass’, as he called it: a continuous glass surface which looked like a pointed shard of glass. And so I worked with the architect, façade designers and with the system designs to achieve a very high-performance façade using an active façade system, which incorporated automatically-controlled roller blinds,” says Guthrie.

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    The Shard Tower in London by Alistair Guthrie and Pritzker architect Renzo Piano. Photography by Daniel Imade

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    A cross-section of the Shard Tower's triple skin facade. Image: Arup 

    “We had a very low level of reflectivity on the glass which did exactly what the architect wanted to do; to allow the passing clouds to be seen in the façade. To achieve that – and a very efficient façade at the same time – was quite a highlight for me.”

    Guthrie further notes that while these technologies have achieved great results in the past, we’re nearing the peak of their ability.

    “We’ve begun to reach the maximum performance of 100 per cent glass façades, so if we want to improve performance beyond what we’ve now achieved – which is a good ambition – then we need to look at composites of other materials with the glass to provide improved performance,” he says.

    “Moving away from 100 per cent glazed to incorporate other materials in the overall façade will be necessary in the future as we seek to [further] improve the performance.”

    A study performed by engineering company Cundall in 2013 compared nine façade types, ranging from full-height glazing to punched windows with 33 per cent glazing. This study revealed the validity of Guthrie’s stance.

    Façade modelling – daylight and thermal performance’ demonstrated that punched windows don’t just outperform full-height glazing on thermal performance measures (for instance, peak cooling demands and number of hours exceeding 26, 28 and 30 degrees Celsius per annum). Somewhat surprisingly, they also perform better on measures of ‘useful daylight’, which incorporate such additional considerations as glare and reflection.

    That said, the study only analysed a singular building in a singular climate. It also failed to consider overshadowing from other buildings, which is likely to reduce solar gain and useful daylight and warrant increasing glazing in areas.

    THE NEXT FRONTIER

    Nowhere is it more important to achieve sustainability than in tall buildings. In the entire history of global skyscraper construction, we’ve built 3,778 towers over 150m in height. Only four of these have ever been demolished.

    What does this mean for us going forward? According to Oldfield, it means that poor-performing skyscrapers being built in Australia now will still be performing poorly in 50 years’ time. By then, the climate is likely to be much hotter.

    Guthrie agrees with Oldfield and says that improving façade design will have the biggest impact on the environmental performance of our buildings. This aspect of the design is by far the biggest player in the energy consumption of the building.

    “My view on how we should go about that on our towers is to [move] away from flat, curtain-wall-type systems to make way for more shaped façade systems. [These] have much more potential to have better performance characteristics for solar shading,” he says.

    “If we can maximise the daylighting and minimise the solar gain on these façades by using shaped façades then that would be the way to go. That will automatically reduce our reliance on mechanical systems, as we’ll need less of them. I also think that in some climates, it will give us the possibility of open façades on our buildings, thereby [further] reducing the reliance on mechanical systems.”

    While Guthrie is excited by the idea of improvements in alternative energy-harnessing technologies that can reduce the environmental impact of a building, he is wary of architects using them to make up for the poor design of our buildings.

    “I think that when we get the design right – [both] the façades and the systems – then the renewables that we can use will have a bigger impact,” he says.

    “Just putting them there to make up for poor design is definitely the wrong strategy.”

    Guthrie is also interested in the potential of vegetation on the façade of the building to be used to reduce environmental impact. For example, for the climate and type of city landscape in Melbourne, Guthrie calculates that green walls could reduce the level of pollution particles in the street air canyons by 20 per cent, and could also reduce the peak temperature at street level by as much as 9.5 degrees Celsius.

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    Walan Apartments by Brisbane-based architecture firm Bureau Proberts will be the first building in Australia to use planters on its facade that have the ability to carry substantial volumes of soil, meaning larger trees can grow on the facade 

    This is an even broader approach to sustainability; one that recognises the impact of a building on the environment beyond its own protected energy use; one that only emphasises the importance of calculated and considered façade design.

    Already we’ve seen green façade strategies being used in Australia, most famously at Sydney’s One Central Park (Jean Nouvel and PTW Architects). There are also plans underway in Brisbane and across the world to go further by fixing ‘vertical forests’ to the façades of buildings.

    Walan Apartments by Brisbane-based architecture firm Bureau Proberts will be the first building in Australia to use planters on its façade that have the ability to carry substantial volumes of soil. This means that larger trees and shrubs that you wouldn’t see on standard green façades would also be able to grow on the side of the building.

    Another two-tower project in China by Italian architect Stefano Boeri is slated to incorporate 1,100 trees and 2,500 hanging plants on its façade. Early modelling suggests that the towers will be able to absorb some 25 tonnes of CO2 each year and generate 60 kilograms of oxygen per day.

    Just this year, researchers at the University of Minnesota and the University of Milano-Bicocca announced that they have created a new generation of photovoltaic windows that will not require any bulky structure to be applied onto their surface. This is made possible by the fact that the photovoltaic cells are concealed within the window’s frame.

    Whatever the case, it appears that two movements within the design community have formed when it comes to façade design, even though they share the same end goal: to improve the environmental impact of tall buildings. The first ‘movement’ aims to improve the performance of glazing, so that views out of a building aren’t affected. The second advocates the provision of more solidity in façade design for improved thermal performance.

    Of late, technological advancements such as photovoltaic windows and new research demonstrating the benefits of vegetation on façades means that we might have to reassess this dichotomy.

    In October 2013, it was announced that the ZhongRong Group intended to rebuild the Crystal Palace as part of a £500 million project. Let’s hope that, if it goes ahead, they consider high-performance glazing at the very least.

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