In 1931 the Empire State Building opened its doors as the tallest building in the world – a record that remained unbeaten until as recently as 1970. Back then, the builders and architects of Manhattan’s 102-story Art Deco masterpiece were focused solely on creating a symbol of progress and modernity following a time of great depression in the USA. Today, however, there is another – far more pressing – consideration for any construction professionals creating something new or renovating a structure that already exists: sustainability.
The world is facing a climate crisis, one where the average global temperature is expected to rise by 1.5 degrees Celsius by 2050, and experts suggest 1 million species – an unthinkable amount – could become extinct in that timeframe. If we, the construction community, stand any chance of reducing the long-term impact of climate change, we must embrace sustainability and make significant changes.
With climate change at the forefront of our thinking, we must ask the following questions: is glass a sustainable building material? Is it a better choice than brick, for example? Are there ways that the sustainability of glass can be improved?
To all three questions, we say yes – and so too do the experts who are tasked with researching this subject.
In this blog post, we will demonstrate how we have come to those conclusions. To do so, it is necessary to break down the use of glass as a building material into three distinct parts:
- The production of glass;
- The day-to-day use of glass; and
- The disposal of glass.
Let’s start with its production.
Is the production of glass sustainable?
Manufacturing glass requires a significant amount of heat, created by furnaces that operate at temperatures between 1,700 and 2,000°C. Such an extraordinary amount of heat – necessary to exceed the melting point of the raw materials (sand, soda ash and limestone) – is created by burning fossil fuels including oil and natural gas. In comparison, the temperature of an industrial brick kiln is far lower – between 700 and 1,100°C – as are the emissions that are emitted during production.
As a useful comparison, manufacturing a kilogram of bricks produces 0.24 kg of CO₂, whereas a kilogram of glass produces 0.85 kg of CO₂. While glass’s embodied emissions are three times higher, the two pale in comparison to stainless steel, a material that produces 6.15 kg of CO₂ for every kilogram created.
In short, the production of glass is the least sustainable part of its current lifecycle due to the emissions that are released. But its story is one of redemption because glass really comes into its own once installed and we look towards its day-to-day use.
Is the day-to-day use of glass sustainable?
When assessing the day-to-day sustainability of glass as a construction material, we are, in essence, talking about its contributions to your building’s energy efficiency. Firstly, by increasing the amount of glazing in a project, you are also increasing the amount of natural light that is allowed to flow in. This, in turn, reduces the amount of artificial light needed for illumination – specifically during early mornings or late afternoons – and the amount of electricity (much of which still comes from fossil fuels) needed to power the lights.
Then there are the thermal characteristics of glass – technologies such as double or triple glazing with an inert gas between the panes and invisible low-emissivity coatings all ensure your home is kept warm in winter and cool in summer. With these things in place and the glazing connected to an advanced control system, you can cut your energy consumption by 50%. What’s more, the total CO2 emitted by manufacturing efficient double glazing is offset between three and 10 months after its installation due to the CO2 saved from heating and electricity.
The more glass you have, the more efficiencies are available. To illustrate the impact of larger windows, Glass for Europe calculates that a building with 10% glazing requires 36 kWh per metre square each year to heat it; a building with 40% glazing, on the other hand, requires just 30 kWh per metre square each year.
Brick certainly has plenty of thermal saving opportunities, but it doesn’t have the transparent qualities that can lower energy consumption for the purposes of lighting.
Is the disposal of glass sustainable?
On the face of it, disposing of glass should be very sustainable. After all, it is cited as one of the best materials to recycle. Indeed, the UK Green Building Council believe that 35% of raw glass material used in construction can be replaced by cullet, otherwise known as recycled glass – that’s because for every 10% of cullet incorporated into the mix, the amount of energy used reduces by 3%. Furthermore, 250 – 300 kilograms of CO2 emissions are saved for every tonne of cullet that is added to the furnace. The problem, however, comes when impurities are accidentally added to the mix when the glass is being collected. By inadvertently incorporating metal filings that are too small to see with the naked eye, you run the risk of experiencing nickel sulphide inclusion, whereby glass can spontaneously smash without any warning at any point in its lifecycle.
If we were to rate the sustainability of glass, we would do it just like this:
The manufacturing of glass: A sustainability score of 3/10
The day-to-day use of glass: A sustainability score of 9/10
The disposal of glass: A sustainability score of 5/10
We have big plans to become net zero (contributing no more greenhouse gases to the Earth’s atmosphere than the amount taken out) by 2030. We will do exactly that by improving the sustainability of our supply chain (reducing transport emissions) and making the manufacturing process far more energy efficient. It is going to be a long journey for not just the glazing industry, but the architectural sector as a whole – we hope you join us for the ride.
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