From small residential buildings to major infrastructure projects, modern methods of construction (MMC) – offsite manufacturing and new onsite techniques – have been making a positive impact on productivity.
Cost and time savings resulting from the use of these methods were highlighted in the Association for Consultancy and Engineering's (ACE's) Project Speed and off-site manufacturing report published in February.
"The experience of ACE members, backed up by research from the National Audit Office, management consultant McKinsey and others shows that using offsite manufacturing at scale can routinely reduce construction time and cost by between 30% and 50%. Applied to £11.7bn of planned infrastructure spending 2022/3 to 2024/5, this would equate to a benefit of £3.5bn to £5.9bn," the report states.
"Could we get to a point where modular construction assets are leased, and they are taken back?"
An example of faster delivery using these methods compared to traditional methods is the Two Fifty One multi-storey residential tower in London. With 70% of the frame manufactured offsite, the overall programme was cut by 33% to 120 days by removing onsite activities from conventional construction.
The report also emphasises offsite manufacturing's sustainability benefits and its role in improving worker safety, as a factory is a far more predictable setting than a physical construction site.
MMC presents an opportunity for the construction industry to reduce waste, use more sustainable materials and cut carbon emissions. As a result, ACE head of policy Guto Davies says that wider adoption of offsite construction can help the government meet its net zero ambitions.
Sustainability
Talking about precast construction of flat panel units, WSP MMC Lead for Property and Buildings Dan Hagan says that offsite manufacturing could facilitate their construction using less Ordinary Portland Cement (OPC) and more ground granulated blast-furnace slag (GGBS), a by-product from the blast-furnaces manufacturing iron. As a result of the greater control within the offsite manufacturing environment, GGBS is a viable alternative to OPC and is more environmentally friendly as no virgin materials have to be used and it has less embodied CO2.
Hagan says that the curing process for concrete using GGBS takes longer, and so it is important for all parties to understand that. He adds that a higher amount of GGBS was used for precast panels constructed for the Grange University Hospital project in Wales, which still opened four months ahead of schedule.
This is because offsite construction removed onsite construction processes and because the panels could be delivered when needed on site and then assembled quickly.
Offsite manufacturing can lead to a greater use of more sustainable materials like timber and hempcrete – a bio-composite material. Although these can be used insitu, they are less resilient to the effects of weather, according to WSP director and net zero carbon lead for property and buildings David Leversha.
"Taking them into an internal factory environment where you can put your hempcrete and your wood shavings into a preformed timber cassette, your productivity goes up through the roof. It's not just about quality control, it's about certainty of program," he explains.
"If coordination does happen, it's late in the process"
Housing developer Greencore uses a closed panel timber frame – complete prefabricated walls with window and door openings – which are manufactured offsite and insulated with natural materials such as hemp, lime and wood-fibre. A whole life carbon emissions assessment on a typical Greencore house conducted by WSP showed that it produced negative whole life carbon emissions of minus 278kgCO2e/m2, compared with Royal Institute of British Architects' 2030 target of producing 625kgCO2e/m2 for domestic housing.
Waste reduction associated with the construction of a given element is another major environmental benefit of the use of MMC.
This waste reduction comes from construction in a controlled factory environment where an element can be made right first time, rather than having to be rebuilt onsite due to construction errors.
Circular economy
MMC can lead to a greater reuse of raw materials, contributing to the efforts to create a circular economy, something the government is keen to promote.
Sweco Architects head of sustainability Elise Grosse defines the notion of a circular economy as "acting in a resourceful way with resources, sharing, rebating, reusing or upcycling them instead of downcycling them through different life cycles."
She stresses that the way cities and buildings are designed can have a major role in the development of a circular economy.
With modular construction, Grosse says that information on each module made available through digital tools can make it "much easier to create new life for them, instead of turning them into waste".
Adaptable buildings
She highlights the importance of adaptable buildings made using MMC, saying that designers have to think about disassembly as well as assembly to distinguish "what is the product and what is the material". Grosse adds that designers should not use materials that cannot be disassembled into new lifecycles.
In terms of designs, WSP technical director for sustainability Tim Danson believes the concept should be "design for deconstruction", so that each modular unit in a building can be taken out as a unit and used elsewhere.
He says that this will be a low carbon solution as it eliminates the need to make new building elements.
"We want to be moving to a position of product as a service, of leasing and hiring, and actually understanding the capital value of something that goes in, but also then understanding its full lifetime recoverability value as well," says Danson.
"Could we get to a point where modular construction assets are leased, and they are taken back, refurbished, refabricated, and then put out back out into industry?"
He says that the industry should aim to keep all the materials in consistent loops of high value applications.
Buro Happold partner Wolf Mangelsdorf believes that improving the circularity of the built environment economy is important, but he says that the biggest challenge in the sector is the design life expectancy of buildings.
Reusing building's parts
He poses what he describes as a "potentially controversial question": "Will people ever reuse complete parts of a building?"
"Can we realistically design a 'product' now – be it a cladding panel or a floor slab for example – that we can, with any confidence, know that someone 30 to 50 years in the future would want to use exactly as it is?"
In London, actions are already taken to ensure that the circular economy is considered in the design of large developments referable to the mayor for planning permission. According to the Greater London Assembly, The London Plan Guidance Economy Statement "treats building materials as resources rather than waste, and puts in place a clear hierarchy, prioritising the retention of existing structures above demolition".
Barriers to adoption
With the government promoting the use of MMC (see box below) and the benefits of these methods widely recognised by the industry, what is stopping them from being more popular?
Davies says one barrier to the adoption of MMC is that investment decisions in the construction industry are focused on the short term. "Sometimes it [the decision] is more about the construction cost than the whole lifecycle value". He says that traditional procurement and contract mechanisms do not allow for the longer term strategic view that these methods require.
He adds that the planning process is another barrier, explaining that clients and planning authorities can have conflicting demands and that this can stifle the potential of these solutions.
The ACE report states that another factor hindering the use of these methods is the lack of integrated supply chains, resulting from fragmented procurement and a lack of early offsite contractor involvement at the concept stage.
Need for scale
Mangelsdorf says that another barrier is that all the efforts to achieve the "industrialisation of construction" have most frequently "taken the form of simplified assemblies of standardised repetitive parts, unsuitable to react to the conditions of site, brief and market", for example.
He adds: "These assemblies are typically highly tuned to proprietary ideas, systems and assembly methods, incompatible with the scale the construction industry requires."
He says that while parts of the industry are successfully industrialised "it still takes too long to bring parts together [when they arrive onsite] and the jack hammer is too often the tool of choice."
"On closer inspection, two things are tripping us up and they are closely linked. Architects and engineers draw up a design intent, but fully rely on the industrialised capacity of the specialist supply chain to resolve design details. Each supplier is resolving what matters to their own industrialised product, and no one owns – or is incentivised to own – the physical coordination needed to resolve issues during construction.
"If coordination does happen, it's late in the process and often reverts to the use of the aforementioned jack hammer," Mangelsdorf explains.
He adds that another barrier to adoption is the industry's attitude to risk. "The construction process is riddled with risk, and we have developed highly refined methods to package it up and pass it on," he says.
"From client to design team, from design team to main contractor, from main contractor to the trades. The risk becomes concentrated at the point where players try to pass it on at design interfaces, where it is neither owned nor resolved."
Breaking down some of these barriers will require a transformation in the way the industry works if it wants to boost efficiency, save costs and help save the planet.
Source: New Civil Engineer
