What will the houses of the future look like?
Construction accounted for 38% of the world’s total CO2 emissions in 2019. If we have any hope of reaching net zero we need to rethink our reliance on steel and concrete and use other more sustainable materials. But what will these houses of the future look and feel like?
The problem with concrete
Concrete is a popular material in construction thanks to its strength, durability and versatility.
It has a downside, however. To bind the concrete, more than 4 billion tonnes of Portland cement are produced each year. The cement manufacturing process releases almost one tonne of carbon dioxide for every tonne of cement, accounting for 7% of human-derived CO2 emissions.
So, what’s the alternative?
The rise of wooden skyscrapers
Since the advent of the first skyscraper more than 100 years ago, steel and concrete have been the go-to material for tall buildings. Could wood provide another option?
Wood is an excellent building material for small scale projects, but there are many reasons why, until recently, no-one has considered building a timber skyscraper.
For one, it’s highly combustible. Wood also bends, warps and softens when it gets wet, greatly reducing its mechanical strength. Timber is also susceptible to attack by fungi and bacteria.
But that doesn’t mean it can’t be done. Dr Michael Ramage, Reader in Architecture and Engineering at the University of Cambridge, led a project to design the next generation of skyscrapers out of wood.
The skyscrapers designed by Ramage wouldn’t be made from normal wood, instead they would be constructed from a special lattice of engineered wood, known as cross-laminated timber (CLT).
CLT is made by gluing strips of softwood timber panels across each other at right angles. By removing defects in the wood and alternating the direction of the grain in each layer, CLT can be made as strong as steel.
Skyscrapers made from CLT offer several advantages over steel and concrete. For one, they would be 40–50% lighter, saving on foundation and transport costs. They would also be quicker to build and could be largely constructed offsite.
The main advantage of wood, however, is that, if managed correctly, it is sustainable.
According to Ramage, the sustainable forests of Europe would take just seven seconds to grow the volume of timber required for a three-bedroom apartment, and four hours to grow a 300-metre supertall skyscraper. Canada’s sustainable forests alone produce enough timber to house a billion people.
Trees also absorb carbon dioxide from the atmosphere and store it in their wood. So, constructing cities made from timber skyscrapers would prevent that carbon dioxide from being released back into the atmosphere. Timber buildings are more energy efficient too, as wood is an extremely good insulator, so less energy is needed to keep it warm.
Through the Super Tall Timber project, Ramage led a team which aimed to provide the understanding necessary to design and construct tall buildings using these new materials.
As part of the project, Ramage’s group formed partnerships with architect and engineering firms in the UK and the USA. These led to the creation of conceptual designs for timber skyscrapers in London (300 m), The Hague (150 m) and Chicago (243 m).
The team also studied wood at a molecular scale and discovered ways of strengthening timber through incorporating polymers within its structure, or through thermal and chemical modifications.
“Timber is the only building material we can grow, and every tonne of timber expunges 1.8 tonnes of carbon dioxide from the atmosphere,” says Michael Ramage.
“If all new homes in England alone were constructed from timber, we could capture and offset the carbon footprints of around 850,000 people for 10 years.”
It’s not just skyscrapers that could be made from timber. Many believe that the material could be used to make more traditional homes in Britain.
The project Design optimisation and prototyping for affordable rural housing, for example, is developing a prototype house using a hybrid of whole and milled timber, which is more environmentally friendly. It is also exploring automation and robotic-cum-artisan techniques to reduce economic costs.
Making concrete greener
In the meantime, if we could find a way of producing concrete in a more environmentally friendly way, perhaps we could carry on reaping the benefits of the material.
Professor Susan Bernal Lopez and her team at the University of Leeds is developing and studying sustainable cement alternatives which can be used in place of Portland cement for the production of concrete.
One exciting material, known as ‘alkali-activated cement’, can be created from simple industrial wastes or by-products and could reduce the CO2 emissions associated with concrete production by between 40 to 80%.
At the moment, despite the potential, the performance of alkali-activated materials in the field is not fully proven.
Bernal Lopez’s research uses state-of-the-art techniques to study the performance of the alkali-activated cements to make sure that they are strong, durable and safe for use, even under challenging conditions over decades or more.
The cements undergo rigorous tests in specialist climate-controlled chambers capable of simulating marine environments and the extreme freeze-thaw action of very cold climates.
Bernal Lopez also leads a project called RENACEM, which investigates the chemical reactions and physical processes that can cause cements to deteriorate when they are in contact with atmospheric CO2.
In recent years the use of natural materials such as calcined clays and volcanic minerals as additives in concrete has rocketed. However, there are concerns that these additives could increase the vulnerability of concrete to carbonation, a process where CO₂ enters the material and causes changes to its chemistry and strength. Carbonation can also cause the steel reinforcement present within concrete to corrode.
RENACEM aims to see which chemical reactions and physical processes can cause cements to deteriorate. The interaction of CO2 with cements is of particular interest. Atmospheric CO2 concentrations are at their highest in human history, so it’s essential that modern concretes are robust enough to withstand large amounts of CO2 without compromising their strength.
So, is it likely that these new, environmentally friendly cements will be used in construction any time soon?
“The UK is in a very strong position for the rapid widespread uptake of this technology, as one of the few countries that has standardised these materials,” says Bernal Lopez.
“A significant amount of research is still needed to ensure structural integrity when using these cement and concretes in different applications. It’s also critical that their environmental credentials, recyclability and circularly potential are fully understood, to ensure that these materials are truly environmentally friendly during the entire life cycle.”
“There are already a growing number of companies commercialising different types of green cement and concretes, however, so the low carbon alternatives are already available for non-structural applications.”
With further research, it looks like we are well on the way to more carbon friendly homes and buildings.
Want to know more?
If you’re a UK taxpayer, your contributions helped fund this work, via UK Research and Innovation — the funding body that allocates government funds for research — and the nine research councils.
The Super Tall Timber project was funded by the Engineering and Physical Sciences Research Council (EPSRC).
The project Design optimisation and prototyping for affordable rural housing is funded through the Transforming Construction Network Plus (N+) — a national community which aims to unite and transform the UK construction industry.
Professor Susan Bernal Lopez is supported by an EPSRC Early Career Fellowship Award. Her project RENACEM is also funded by the EPSRC.
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