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Builders’ dirty secrets

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The construction sector is a huge contributor to carbon pollution. Is improvement difficult, given the materials and work practices, or could it be doing better?

One of the most impressive environmental achievements of the last decade has been a near transformation of Britain’s national electricity grid. In the first quarter of 2020, 40 per cent of Britain’s grid electricity was generated from renewable sources – primarily wind and solar.

As Britain locked down in April, its grid went without burning coal for two continuous months – the longest coal-free period Britain has experienced since the Industrial Revolution. Other areas, such as the automotive sector, are also moving in an encouraging direction as it pivots further to electric cars. As we work towards the Paris Agreement target of net-zero emissions by 2050, everything appears to be going well.

Well, almost everything.

One significant sore spot is construction. According to the Global Alliance for Buildings and Construction, the act of constructing buildings, including manufacturing materials such as steel and cement, is estimated to be responsible for 11 per cent of global CO2 emissions. This is known in the industry as the ‘embodied’ carbon. Some independent academics argue that this may even be a low-ball estimate, with the true figure being closer to 20 per cent when alternative methodologies are used. Once you include the anticipated carbon emissions from buildings’ lifetimes – the ‘operational’ carbon – this figure approaches 40 per cent of global emissions.

According to figures produced by Dr Jannik Giesekam, a research fellow in Industrial Climate Policy at the University of Leeds, in absolute terms the overall embodied carbon from just the UK construction sector is as much as 50 million tonnes every year. The construction industry, then, needs to do something about it.

The scale of the challenge, though, can be seen in how the industry has approached the problem. The first serious attempt at identifying a solution was the Low Carbon Routemap to the Built Environment, published by the Green Construction Board in 2013. The report called for an 80 per cent reduction in CO2 compared to 1990 levels by 2050.

“There was a pretty mixed reception at the time when it came out,” explains Giesekam, “Basically, everyone thought it was essential that we do it. And then everyone was astonished at the scale of change required.”

Unfortunately since then, the challenge has magnified: the 2050 target is no longer a mere reduction – but net zero.

To make matters worse, since the 2008 financial crisis caused a brief plateau, carbon emissions from construction have continued to rise every year. “The carbon intensity of those supply chains has been declining very slowly. But what we’ve been doing is building more,” says Giesekam.

In other words, despite the incremental improvements being made to produce building materials more sustainably, the overall amount of building has increased, wiping out the efficiency gains.

What is the industry to do? “The easiest part of the challenge is reducing the operational carbon emissions from buildings,” says Giesekam, “because you can in large part electrify things like heating and so on, and then supply those with renewables. When it comes to production of materials for the buildings, you’ve got far fewer options.”

On the average construction site, there is some scope for greener alternatives. To take one example, in July 2020 JCB announced its first ever digger powered by hydrogen instead of diesel. And hydrogen generators are now available to replace diesel generators too. What is hampering adoption, however, is availability. Because of the ubiquity of diesel generators and diesel fuel, construction companies know they can make a call and have one on site the next day, which isn’t yet the case for hydrogen.

In any case, tools are only a tiny proportion of emissions over the lifecycle of a project. The biggest cause of embodied CO2 is in the raw materials: the steel, cement and bricks that are used to fabricate structures.

This is where the environmental concerns hit against a chemical reality: the production of materials like cement emit significant amounts of CO2 as part of the reaction that makes it. “Even if you can supply it with a renewable source of energy to fuel that process, you’re still going to have around two-thirds of the emissions remaining,” says Giesekam.

This means that engineers are faced with a choice: offset the carbon released, or use an alternative material. In the case of the former, a carbon capture and storage solution could, in the UK at least, in the words of Giesekam “double the cost of a bag of cement”, which may make it a non-starter for construction companies.

The other option, alternative materials, is potentially a much more fruitful route to take. “When was our last innovation in terms of materials?” asks Dr Dan Maskell, a lecturer in the Department of Architecture & Civil Engineering at the University of Bath.

“You look out your window and you see steel and you see concrete. And in terms of modern-day steel and modern-day concrete, they’re over about 150 years old now. When was the last time we’ve really innovated in that sector?”

Maskell is most enthusiastic about the potential for bio-based materials, like straw bale or hemp lime construction – as well as the use of wood fibres and timber frames in place of traditional materials. And though none of these materials are widely used yet, there are dozens of smaller projects using the new technologies.

For example, a company called ModCell has used straw-bale technology on housing projects, schools and office buildings.

Similarly, Adnams’ brewery distribution centre in Suffolk is one of the largest buildings in the UK using hemp lime, which offers better insulation than standard materials. The walls were made from over 90,000 blocks manufactured from locally grown hemp, lime and quarry waste.

Maskell is also keen to point out that new materials are not just for small or low-lying buildings. In fact last year in Brumunddal, Norway, an 18-storey entirely timber frame tower was completed and a similar 70-storey tower has been proposed in Tokyo.

However, there is some reticence within industry to switch to these newer materials.

“There’s been a lot of false dawns with people offering all sorts of clever, innovative new products, but they’ve got to last,” says Chris Harrop, director of sustainability and marketing at Marshalls plc, a supplier of building materials, “If you build something with a very clever low-carbon product, you need to know that it will still be there in 60 years or 100 years time. And it’s probably one of the reasons the sector has been a little slow.”

Given this, Harrop believes that one of the most effective means of reducing embodied carbon could be a rather unusual candidate given its reputation: concrete. Despite the carbon intensity of mixing cement, the impact of concrete is still 49 per cent lower than traditional clay bricks, according to the Environmental Product Declaration system. So, if builders can be persuaded to switch to concrete bricks, it could make a real dent in emissions.

There is also scope to optimise just how sustainable concrete bricks are compared to their clay counterparts. “You want to have the maximum amount of strength for the minimum amount of cement,” says Harrop, “So you can reduce it until you can hit that target of strength, but then you can use substitutes to also help in the binding of that product that then don’t affect its performance over time.”

If the potential material solutions are out there, why haven’t new materials taken off in a big way yet? One factor may be economics. According to Maskell, it isn’t unusual for 50 per cent of material produced or used on construction sites to go to waste, but construction firms are not as worried about this inefficiency because the major expenses are not just materials, but also time and cost of labour. On the balance sheet, the cost of the actual materials is less important.

“The reality of it is that the production of those is tiny compared to the main sources of cement that we’re using at the moment,” says Giesekam. What will it take to change things?

“Ultimately it comes down to policy and guidance in terms of planning control, or building regulations,” says Maskell, who believes the industry needs to be challenged to work to a higher standard. “I don’t think it’s a technical issue at all. I think we’ve got it – we’ve demonstrated that we can do it.”

Some regulatory changes are already making an impact. For example, the EU directive on Medium Combustion Plants has come into into force, including in the UK, with air-quality requirements affecting the use of diesel generators on much construction equipment. This will inevitably lead to the wider deployment of hydrogen and renewable alternatives.

Changes are also being made by local authorities. For example, the Greater London Authority insists that large building projects in the city now conduct ‘whole life’ carbon assessments, which evaluate the carbon impact of a development through construction, use and even demolition.

At the moment, this only affects something like 150 of the largest projects – though the implication is that such demands could cascade down in future years and raise the requirements for smaller projects too.

Giesekam points to a similar requirement that was introduced in the Netherlands several years ago. “They basically gathered the data for years and got the industry familiar with the process of doing an assessment, understanding the data and what the impacts of the different materials were. And then once they had that data in place, they could set targets,” he explains.

This means that instead of setting strict prescriptive requirements on how projects are designed, such as specifying the proportion that must be made from alternative materials, as France does, carbon can be reduced by focusing on outcomes and leaving builders more flexibility on how to achieve it.

Giesekam expects these sorts of requirements to be rolled out by other local authorities in the next few years too, but even just a handful making the change could make a big difference. “Even if it was just Manchester plus London plus Bristol and a couple of other places, you’re going to cover a big part of the UK construction market just there anyway.”

There is one final factor that could make a big difference: standards. “We don’t have any sort of routine assessment of embodied carbon in place,” warns Giesekam.

“I think the most important thing is that everybody starts to use the same language and the same methodologies,” says Harrop, who points to the fact that as things currently stand, there are few consistent standards for measuring embodied carbon, which makes it difficult for construction companies to compare the environmental impact of different products and materials.

Harrop argues that the current situation, where companies and organisations can choose their own measurement standards, isn’t really working. “I have a methodology and it just so happens that my methodology makes my product look better than your product,” he laughs.

He points to the PAS2050 standard, which is used to calculate the carbon footprints of goods and services as a model. Another system is that of Environmental Product Declarations, but these are voluntary, and only a small proportion of the construction industry uses them.

“Unless you’ve got a requirement to do it, it’s going to be the minority of the industry that does it,” says Giesekam, explaining that, “Best practice in the UK is about as good as best practice anywhere in the world. But the bulk of UK practice is below what a lot of our European neighbours are already doing.”

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