The climate emergency demands a laser focus on reducing carbon emissions across the built environment. So, can offsite construction be used to deliver on our decarbonisation goals?
The new report from the Supply Chain Sustainability School on Whole Life Carbon Guidance for Offsite Construction sets out to answer this question. In our research, we found promising examples of the offsite sector making a difference, from manufacturers cutting embodied carbon through optimised use of materials and renewables to industrialised retrofit techniques minimising disruption for building occupiers.
The most compelling arguments for the carbon benefits of offsite come from the reduction in time on site and the optimisation of logistics – in other words, in the construction phase. This is not surprising, considering it shifts activity to the manufacturing facility and means deliveries can be consolidated from gate to site. Studies have demonstrated 30% fewer emissions from energy use for offsite projects than conventional – even when factory energy use is included – and 60% emissions reduction from transport to site for materials and workers.
But to really cut into the whole life carbon of projects, especially in infrastructure, tackling the carbon locked up in extraction, processing and manufacturing of materials and products must be a priority. In most cases, this represents a climate impact hotspot: as an example, for High Speed 2 (HS2) Phase 1, almost half of the projected carbon footprint is attributed to construction material.
Designing for manufacture and assembly, rather than fabrication onsite, can encourage optimal use of materials, bringing about emissions savings in this “product” stage. In an example from the residential sector, life cycle assessments of two Tide Construction modular developments found embodied carbon savings of 41% and 45% against conventional benchmarks, attributed to efficiencies in design enabled by the offsite system. Material use can also be more easily controlled in the factory environment, with less waste and damage to materials.
In recent years, examples of embodied carbon reductions through design for manufacture and assembly have emerged in infrastructure, including the streamlined modular design of National Highways’ new motorway gantries, and the elimination of concrete foundations in Network Rail’s lightweight Flow bridges. Of course, offsite methods will not be the lowest carbon solution for every project; if a nature-based flood management system can be used, this is a clear winner over a precast concrete flood wall.
The report also considers how to maximise carbon reduction opportunities. A clear driver for this is leadership from clients and designers, specifying and advocating for low-carbon options consistently. In all projects, the opportunity for carbon savings is greatest at the early stages. This becomes even more important when understanding the full potential of integrating premanufactured elements. The Environment Agency is leading from a procurement perspective by introducing carbon reduction into its minimum technical requirements, including caps on embodied carbon values for both structural and non-structural concrete infrastructure.
On the whole, similar materials are used across offsite and conventional construction, which begs the question: “Can design for manufacture and assembly make it easier to incorporate new low-carbon materials?” It is too early to say, but the early collaboration between manufacturers with knowledge of systems and materials and design teams equipped with digital design techniques can be a catalyst for innovation.
Underpinning all these efforts must be effective carbon data management and transparency. Throughout our research, numerous organisations reported this as a challenge. Data collection processes should be in place across the supply chain, following PAS 2080. For product data, manufacturers and suppliers need to work towards producing specific emissions factors, such as through the EPD process, and clients and procurement teams should request these and reward best practices.
A key takeaway from the project has been the need for low carbon to be a goal from the outset; if this is the case, and the brief suits the adoption of offsite construction, it can be used in service of this goal.
In other words, adopting offsite techniques does not guarantee a low-carbon outcome. To understand the benefits and trade-offs of offsite in more detail, robust data collection is needed, supported by early collaboration and engagement with supply chain partners.
