Using DfMA to reduce wastage
On the upgrade of Davyhulme wastewater treatment works, DfMA saved an estimated 15-20% concrete and steel in the construction of concrete tanks.
A modular, factory approach has been talked about for years as the best way to increase the productivity of the construction industry. The drive for net-zero carbon should provide the impetus to finally make it mainstream.
Where are the carbon hotspots in construction? Waste is one.
Wastage of materials and resources is an endemic problem when constructing buildings and infrastructure. Projects are still being delivered where up to half of the materials brought to site are wasted and end up in landfill, not in the finished asset.
As well as adding unnecessary cost, wastage increases the carbon footprint of a project. Carbon estimates at the design stage usually fall significantly short of the figure on completion: carbon arising from producing and transporting materials is known as embodied carbon. If up to 50% of materials delivered to site go to waste, the embodied carbon footprint will be up to twice as big as calculated at design. Delays associated with traditional construction methods add further to the carbon impact, due to the emissions associated with transport and labour.
This matters. The UK government is committed to reducing national carbon emissions to net-zero by 2050. While homes can be powered with renewable energy, it is a lot harder to decarbonise quarrying and mining, cement and steel production, at least in the near term. As the rest of the economy gets greener, construction will proportionally account for an ever larger share of national emissions. Until zero-carbon materials become a reality, the greatest strides to decarbonise construction will be by cutting the quantities of materials used.
Waste arises from: designs that are difficult to build or that ignore standard dimensions and units, resulting in leftover quantities; over-ordering due to caution or uncertainty; transporting and storing unused materials; weather and accidental damage of materials in storage; poor supply chain co-ordination; and human error. It is not just big infrastructure that is responsible: the issue affects construction projects of all kinds and at every scale.
A factory approach
Reduced wastage and increased efficiency have long been arguments in favour of design for manufacture and assembly (DfMA), where designs are based on modular, standardised components, built in a factory and then assembled when they arrive on site. But the industry has been slow to adopt these methods, even with an apparently clear financial incentive to do so.
DfMA has the potential to make a transformative difference. Waste is driven out at each stage. Design is optimised for manufacture. Manufacturing is resource-efficient. Any waste arising from manufacture is recovered for recycling. With the assembly of components becoming the dominant activity, construction sites. Factory-based manufacturing simplifies supply chain logistics, with raw materials being delivered to manufacturing hubs rather than to multiple construction sites. Modules are delivered from factory to site only when needed, using ‘just in time’ principles, so there is reduced risk of wastage resulting from sequencing errors, no stockpiling and over-ordering, and no accidental damage, as the modules are lifted straight into position on delivery.
Recipe for reduction
In 2013 the UK government’s Infrastructure Carbon Review (authored by Mott MacDonald) set out a carbon reduction hierarchy. DfMA is high up in that hierarchy.
- Zero emissions: Build nothing.
- 80-100% carbon reduction: Build less – plan and design to maximise the use of existing assets and minimise new construction – innovate to improve performance, capacity, service quality, reliability and resilience; reward efficiency. If DfMA were developed to create a wide-ranging catalogue of standard components used in multiple applications – what’s known as a platform approach – it would be easier to adapt assets to changing needs, and to refuse components between assets.
- 50-80% carbon reduction: Build smart – use lean design and DfMA to minimise resource consumption; specify low carbon materials and delivery processes.
- 10-50%: Build efficiently – embrace new construction technologies and eliminate waste.
- 5-10%: Optimise in use – drive energy efficiency. Build quality is important for achieving specified insulation and air tightness in buildings and high performance in dynamic structures and machinery. Standardised components can be maintained more easily.
DfMA is closely allied with BIM, which is increasingly data-rich. MOATA Carbon Portal is our tool for modelling the capital and operational carbon of new assets. It is integrated with BIM, enabling designers to try out different options, gauge their carbon emissions, and iteratively drive the carbon footprint down. Carbon Portal is built on the infrastructure industry’s most comprehensive carbon database. As part of our MOATA digital platform, Carbon Portal is linked with a wider range of solutions to drive efficiency and value throughout construction and asset operation.
Designing for the requirements and possibilities offered by manufacturing, plus the level of control that manufacturing offers means DfMA enables us to save resources or achieve more with a given quantity. On the upgrade of Davyhulme wastewater treatment works in the north west of England, DfMA saved an estimated 15-20% concrete and steel in the construction of concrete tanks. Department for Education figures show that modular schools provide 10% more floor area than those designed in a traditional way, using the same quantity of materials (excluding waste). This is achieved by making buildings more compact – for example, reducing ceiling heights by integrating ductwork into floor/ceiling panels. An office building designed by architects Bryden Wood as a showcase for platform DfMA (P-DfMA) is expected to deliver embodied carbon reductions of 19% per square metre in floors and walls, 36% in the substructure and 20% in the superstructure and facade.
Turning DfMA into mainstream practice could make a major contribution to decarbonising construction. But it won’t happen unless infrastructure owners, designers, constructors and the supply chain work together. How to do that is mapped out in the international standard for managing carbon in infrastructure, PAS 2080 – also authored by us, and we’re the only consultant to be globally certified. PAS 2080 provides the ability to align the whole supply chain with the net-zero goal.
- This article is the second in our series looking at the beneficial outcomes that can be achieved by DfMA approaches. Read our first article on the social outcomes here.
- In our role as integrator of the Construction Innovation Hub (CIH), Mott MacDonald is helping to make develop platform-based social infrastructure – a set of components that can be utilised to build schools, hospitals and prisons - a reality. Find out more at www.constructioninnovationhub.org.uk