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Are glass towers heating up the streets? If so, what can we do?

Photo by Christian Wiediger on Unsplash

SPECIAL FEATURE: Tackling the urban heat island effect is a big burly challenge with so many interrelated factors it’s enough to make anyone’s head spin. Every street microclimate has its own set of challenges – dark pavements, lack of airflow, and now, mirror-like glass facades are a growing, and rather contentious, concern. So does this spell the end of glitzy fully-glazed glass towers in hot sunny cities like Sydney and Brisbane? The Fifth Estate investigates.


Glass technology has come a long way over the years.

In the past, windows were tinted to keep the heat out but this also blocked out a lot of the useful visible light.

Nowadays there’s spectrally selective glass coatings available that allow far more of the visible spectrum through (light) while blocking non-visible parts of the spectrum that carry heat.

These new-age products have facilitated a huge leap in building energy efficiency – not to mention the amount and quality of natural light in offices – with the top end products capable of a light-to-solar gain (LSG) ratio approaching 2.5, letting in almost 2.5 units of light for every one unit of heat energy.

Without this, it wouldn’t be possible to have windows of 2.7 metres or higher in buildings.

The flip side of this is that the heat doesn’t disappear. When the sun hits the window at a sharp angle, according to Alex Kobler, sustainability section, manager and principal of Wood & Grieve Engineers (now part of Stantec).

“It’s like skipping a rock across water” and most of the solar energy is often deflected down into the urban scape, Kobler says.

What’s happening, according to University of New South Wales academic Dr Riccardo Paolini, is that mirror-like surfaces reflect solar radiation at an angle equal to the angle of incidence.

Fully glazed façades, especially with reflective treatment, behave much like mirrors, and therefore during the central hours of hot clear-sky days will deflect most solar radiation downwards, towards other buildings or the street pavement, which are typically made of asphalt concrete and absorb 90-95 per cent of solar radiation, releasing it as heat (thermal radiation).

Some solar heat will go into the building, through the glazed windows, but the remainder will be deflected towards other buildings. Depending on factors such as the facades of other buildings and the width of the street, there’s potential for heat to become effectively trapped in at street level.

What can be done about this?

There are many options to mitigate this problem from a building design standpoint such as using reflecting materials and shading devices and louvres, such as horizontal shading systems.

Paolini says with the proper design, shading devices allow light and warmth in during winter and can reflect most of the sunlight upwards during summer.

At a localised level, Kobler says greenery is one of the simplest and most effective options to reduce the impact of urban heat in any form by providing a dual benefit. Established trees provide both shade and additional cooling through a process called evotranspiration.

He says an urban canopy at the ground level protects people from this heat and “as the rays hit the canopy, water evaporates from the leaves.

“This actively cools the air just as sweat cools our skin as it evaporates.”

If greenery isn’t an option, pergolas, fans misters or even water fountains are other options to help keep people cool at the ground level.

Going back to basics

For Fitzpatrick + Partners principal James Fitzpatrick, the exterior heating effect of highly glazed glass buildings is the sort of unintended consequence that happens when building designers lose sight of the root problems they are trying to solve.

Over the years, floor to ceiling glass facades that allow unfettered views have become the norm in commercial office buildings.

As energy efficiency requirements came in, the industry responded with new glass technologies that might have solved the energy efficiency problem but inadvertently created another by contributing to the urban heat island effect.

It’s important to take a step back and ask if all this glass is necessary, or even desirable, in the office environment

Fitzpatrick says the irony is that preoccupation with floor to ceiling glass is not necessarily driving the best experience for occupants either.

Office workers are often seated right next to the windows where they cop the worst of the sun’s heat that makes it though the glass, as well as direct glare on their computer screens.

Fitzpatrick says it’s important to take a step back and ask if all this glass is necessary, or even desirable, in the office environment.

The way residential homes are designed offer some clues. For example, one strategically placed window might make the most of an expansive view but there’s usually also plenty of blank walls for hanging photos and paintings.

The reality is that in any building, offices included, people aren’t staring out the window all day – they are working on their computers and interacting with people. These spaces should therefore be designed to accommodate these core uses as a priority.

This certainly doesn’t spell the end of sweeping views – just a more considered approach that might actually promote greater appreciation of what can be seen outside by creating contrast and variance.

“You need a negative to understand a positive,” he says, suggesting there can be a psychological advantage to limiting access to views.

“Our approach is ask ‘why do we have all this glass’ and ‘do we need it to create pleasant working environments?’”

From that starting point, Fitzpatrick says there’s a myriad of creative facade options that solve more than one problem at once.

Shading devices can not only create a pleasant dappled light inside the building, but also help bounce some of the sun energy in different directions rather than just towards the street.

The industry is starting to recognise the value of designing workspaces that promote the use of space in a more practical way, evidenced by the rise of office spaces on offer with clever fitouts and furnishings rather than empty boxes that rely on the view as their only selling point.  

It’s not just glazed glass facades – any type of solid metallic material will have the same effect. One alternative is using textured panels that behave “a bit like playing 8 ball” by bouncing sunlight off in all different directions.

He says the industry is starting to recognise the value of designing workspaces that promote the use of space in a more practical way, evidenced by the rise of office spaces on offer with clever fitouts and furnishings rather than empty boxes that rely on the view as their only selling point.

The more sophisticated players in the industry are moving away from the “sterile” office environments that we’ve trudged towards since the 1920s to something that is closer to the home environment.

Is anyone doing anything about this?

Sydney’s western suburbs are particularly prone to the urban heat island effect, and this is where much of the research and innovation in this area is focused.

Some councils are looking to better understand the relationship with glass facades and the urban heat island effect, including the City of Parramatta.

City of Parramatta manager, environmental outcomes, city strategy Helen Papathanasiou says that because the energy building requirements over the last few decades have focused on solar energy entering the building, it’s become common to use heat reflective glass to keep heat load out of the building.

She says that the problem is worse at the ground level because at higher levels of the building there is stronger wind that carries the heat away.

Options on the table include mandating green or painted white roofs, and depending on the conditions, requirements for some buildings to put in shading to minimise solar reflectivity, or another type of façade treatment.

There are some innovative options out there such as “cool façades” used in Japan that have water running through them like a cool skin.

“There are some really high tech interesting approaches.”

As the city expands, the likelihood is that there will be more vertical surfaces than horizontal. “The impact could be significant on a cumulative basis”.

Performance-based targets could be the way to go

Mitigating glare off a façade is something the building industry is already used to, and it’s not unusual to see development controls limiting the reflectance of visible light.

Alex Kobler says that’s why you don’t see “shiny jewel” buildings in Australia like in some other parts of the world.

“The challenge should be on the design team to develop a functional solution, otherwise it prevents design excellence.”

The engineer says he’s started to see a few conditions of consent being placed in development application approvals with clauses specifically limiting the solar energy reflectivity off a building’s façade in parts of Sydney and Brisbane.

Ideally, he says these stipulations will provide a performance metric to design to and avoid prescriptive elements (such as recommending against spectrally selective glass or requiring specific shading devices) because “the challenge should be on the design team to develop a functional solution, otherwise it prevents design excellence.”

He points out that it’s important to view this heating effect in larger context to avoid inadvertently worsening the problem.

Some sources contacted by The Fifth Estate believe that glazed facades are having a negligible impact on the urban heat island effect, and that the environmental perks of energy efficient glass outrank the negative impacts the material might have on urban microclimates.

Less energy efficient glass could lead to a scenario where more airconditioning is used to keep the internal building temperatures comfortable and therefore more residual heat released by HVAC units onto the street.

There’s also the additional emissions to consider from cranking up the airconditioning.

Some sources contacted by The Fifth Estate believe that glazed facades are having a negligible impact on the urban heat island effect, and that the environmental perks of energy efficient glass outrank the negative impacts the material might have on urban microclimates.

The thinking is that building materials like concrete and asphalt that absorb heat and radiate it back at night are a far bigger concern when compared to glass.

What the new building code says

Dr Riccardo Paolini says the new building code (the National Construction Code released in 2019) guides towards performance-based design and improved use of solar shading.

However, he says the performance-based approach still needs to fully permeate the construction sector, against the business as usual.

He says Australian universities are training a new generation of architects who can design net-zero energy buildings, namely energy efficient buildings where the on-site renewables cover all the energy consumption, leading the energy bills to zero.

Although this is a promising start, he says that part of the code can be enhanced and made more robust in the interests of reducing the overheating of cities.

“A performance-based approach is fundamental in achieving better quality for the building stock. We cannot expect different results by doing over and over the same things.”

Speaking at Tomorrowland19, Arup principal Robert Saidman said that it’s good to see legislation shifting the industry away from highly glazed, highly transparent commercial buildings.

“Gone are the days of full height glass with very little protection.”

He said it “creates a bit of fun for designers” to devise the exact shape and size of a shading device to maximise performance while still preserving views.

The new code will also drive the façade industry – namely glazing technologies – even further.

He says most projects currently on the drawing board are looking at their building envelopes “very differently”.

“We look forward to the day when shades are not seen as a bad thing.”

3XN partner Fred Holt, also a speaker to Tomorrowland, said that building codes in most countries are changing to drive energy efficiency and other environmental outcomes.

James Fitzpatrick believes that enforcing building codes are not always the answer to achieving better design outcomes on issues like energy efficiency and the urban heat island effect.

He says that codes drive industry to find ways around the requirements with new technologies that might inadvertently create a new problem.

Each project comes with its own complex set of problems and should be treated on a case by case basis.

“Let’s just solve the problem by solving problems.”

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Comments

4 Responses to “Are glass towers heating up the streets? If so, what can we do?”

  • Neal Mortensen says:

    Around 1970s an American architect had a eureka moment when he realised that energy efficient buildings rely on the balance of glass, mass, insulation. and these relationships will vary from place to place. Sensible shading and orientation were a given.
    As an architect I did my own research and experimenting I developed a formula for designing prestige houses in the Sydney area that required no mechanical heating or cooling.
    Architects have to change their obsession with simple glass boxes and take on the challenge of balanced complex designs.

  • Tina Gibson says:

    Great article highlighting all the issues that should be addressed . As the perfect example of how not to do something the new theatre at the Queensland Performing Arts Centre will be a totally glazed facade catching east and west sun. The heat load and air conditioning costs will be enormous. No consideration is being made for the occupants of the facing buildings who will have problems with glare. This is irresponsible design by the government who should be setting a better example.

  • Rita de Heer says:

    Maybe the first thing to do could be to turn off unnecessary lights at night. Most buildings are ablaze with light 24 hours a day.

  • Luke says:

    Great article, totally agree that starting with the fundamentals of the architectural design. However I’m afraid thie arrogant and selfish starchitects and developers fail to hear or accept these priorities.
    Look at the latest works of the big names – for high end aspirational clients and you see horrific failures in terms of the fundamentals you highlight. And the scary reality is that these buildings will often receive awards from those who declare a climate emergency??? And go on to inspire more architects, developers and governments to create architecture with a half hearted response to ecologically responsibility.

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