Tackling greenhouse gas emissions and moving towards net-zero carbon are going to become increasingly important to construction
The use of more sustainable materials, reduced transport miles and low-carbon alternatives to cement and steel will shape future design, planning and build. Governments have introduced commitments to reduce their greenhouse gas emissions and the construction industry will be expected to contribute to these drives, pushing towards becoming net-zero carbon.
While much of the sustainability focus has been on the function of green buildings post-handover, it needs to also include the carbon emissions emitted during the construction process, known as embodied carbon.
Embodied carbon covers the emissions from both materials used and the construction of a building. Emissions related to materials include extraction, manufacture (including energy use) and transport.
It is estimated that globally, the construction industry accounts for around 39% of energy-related and process-related carbon dioxide emissions. The majority (28%) of those emissions are emitted during use, for instance through the energy required to cool or heat a building once it is occupied. Eleven percent are related to the construction process itself, along with the manufacturing processes of the materials such as steel, cement and glass. Where operational emissions can be reduced, through more efficient use or upgrades, upfront carbon once emitted, cannot.
In its 2019 Global Status Report for Buildings and Construction, the UN Environment wrote that “the sector is not on track with the level of climate action necessary” to mitigate carbon emissions. Far from reducing, emissions from the construction industry continue to rise, due mainly to pressures from population rise and higher floor areas being built in major city sites.
The World Green Building Council has forecast that for future construction, half of a building’s carbon footprint will be embodied. It has set targets that by 2030 the industry’s embodied carbon emissions will fall by 40%, and that by 2050 buildings will be net-zero for their entire lifecycle – including use and demolition.
As the industry pushes towards net-zero carbon, what role can construction technology play towards meeting future targets?
The future job site is going to be more automated, with fewer staff and have a greater emphasis on the importance of data. Robotics, automation and connected vehicles will become more prevalent, introducing significant change to how a site operates. Tangible examples that are growing in use include modular construction and 3D printing.
Modular construction takes a manufacturing approach to construction, moving the industry towards Pre-Manufactured Pre-finished Volumetric Construction. Much of the work is done in factories offsite, with units then transported to the site. Transport miles must be considered in the total emissions calculation for modular, but materials waste is reduced and fewer people are required onsite for the construction process.
Modular cannot take on the whole build – civil engineering or the infrastructure for instance. It is also less used in the Middle East compared with some other regions, but growing. To become more common, it will require some changes in mindset, as the repetitive construction processes are more akin to manufacturing, so design and materials need to be agreed upfront and there is less scope for change later on. Modular can also reduce the total lifecycle carbon cost, as maintenance requirements post-handover are, according to the Modular Building Institute, about 20% lower, and the building can be disassembled for reuse or refurbishment.
Less advanced in use but also growing, 3D printing has been highlighted as a new front in not just future building processes but also for the environmental benefits it can bring. Fewer people will be onsite and a quicker completion date means lower emissions, including transport miles, during a job. It also introduces the opportunity to use (or reuse) novel materials that may be less carbon intensive. But today, much of the 3D printing underway is still cement-based, and so comes with high levels of embodied carbon.
Data and digitalisation may seem a less obvious opportunity, but these will also drive sustainability and indirectly reduce upfront carbon. Companies are increasingly developing tools to manage onsite operations more efficiently, from materials locations to robotics and cloud-based platforms that can measure onsite developments against plans. Tools such as Holobuilder or Scaled Robotics (to name just two) can compare ongoing construction against plans, allowing developers to quickly spot mistakes and minimise corrective work.
Digital twins of operational buildings are changing the way buildings are planned and maintained, helping to reduce a building’s embodied carbon. By having a digital representation of a building, with sensors and advanced data analytics in the physical asset, a building can be more efficiently operated and maintained once in use. If used well, digital twins will provide early warning for when parts are going to fail, reducing reactive maintenance and also running costs.
And of course drones will also play a part in reducing emissions, both through cutting materials waste and because fewer people will be required on site for work such as surveying. At the most recent Construction Technology Forum, one speaker gave the example of using drones to cut materials waste on site by monitoring earthworks using drones. A previous job had found that there were 20,000 cubic metres of surplus materials, all unaccounted for in the budget. It cost £26 per cubic metre for the materials to be removed from site.
Construction materials and onsite energy
Concrete is a versatile material, but for buildings to reach net-zero, the contribution to CO2 emissions from cement cannot be ignored. It is estimated that about 8% of annual global emissions are associated with cement production of 4 billion tonnes a year, according to Chatham House. It estimates that to meet targets in the Paris Agreement, emissions must fall annually by 16% by 2030.
While processes have improved, increased levels of construction globally mean its contribution continues to rise. Chatham House forecasts that by 2050, global production is likely to reach more than 5 billion tonnes a year.
It is a similar story for steel, also a major contributor to greenhouse gas emissions. It is responsible overall for 7-9% of CO2 emissions, for steel production going to all industry sectors, not just construction.
Improved carbon footprint will happen if pressure from the end user grows. New novel materials could be an approach, but today the industry is missing economically viable low-carbon alternative materials for use in construction. An approach is to replace clinker with an alternative, low carbon material. Whilst there are challenges to overcome, the European Cement Association estimates that the clinker to cement ratio could be reduced by 70%, resulting in a reduction in CO2 emissions of 4% during cement manufacture.
Materials re-use and renewables
The adoption of industry-wide policies during manufacture will also help reduce emissions. These include increasing the reuse of scrap materials, factories using renewables or alternative fuels such as biomass (if from sustainable sources) or hydrogen, and through carbon capture and storage of emissions (although this is expensive and may require incentives. An example in the Middle East is the scheme run by UAE’s Emirates Steel with national oil company ADNOC).
Rethinking onsite energy can also contribute to a reduced footprint. In London, it has been estimated that 7% of nitrogen oxide emissions are due to construction sites. A quarter of that comes from diesel generators to supply power.
By moving to solar photovoltaics (PV), either standalone or (initially more likely) using a hybrid approach of coupling PV with diesel generators, emissions and noise pollution will fall, localised air quality improve and site costs potentially decrease due to lower fuel requirements. Six Construct reported that it had halved its carbon emissions and cut operation costs by 20% by switching to a solar-diesel hybrid system for onsite power on a build in Dubai.
There are many online resources that focus on sustainability in construction. The UK’s Chartered Institute of Buildings for instance includes a detailed set of examples and action plans for reducing emissions in the industry, as part of its Carbon Action 2050 campaign. Similarly RICS has set up a Building Carbon Database to guide industry professionals on emission reductions through a building’s entire lifecycle. And the World Green Building Council includes a range of resources on emissions reductions, including its Bringing Embodied Carbon Upfront report.