Could 3D printing boost housing supply?

Once famous for manufacturing the hardest bricks in the world – used to construct the Empire State Building and Sellafield nuclear power plant – the town of Accrington in Lancashire is now spearheading a very different type of innovation on a vacant plot in its town centre.

Work is underway on what is set to become the largest 3D-printed housing development in Europe. The scheme, for not-for-profit developer Building for Humanity, will create 46 eco-homes for homeless veterans and low-income families.

The mix of two-storey houses and three-storey apartment blocks is being constructed using a giant mobile printer in an automated process expected to cut costs by 25 per cent compared with traditional construction.

Accrington isn’t the only place where the cost-saving benefits of large-scale 3D printing (also known as 3DCP) are being explored as a way to deliver affordable homes, social housing and housing for the homeless.

Harcourt Technologies, the UK distributor of large-scale printers made by COBOD (Construction of Buildings on Demand), has delivered three social homes in Dundalk, Ireland, in the first social housing project to meet a new ISO standard for 3D-printed construction. 

Meanwhile, the US has multiple additive manufacturing projects under its belt, with on-site printers used to deliver social housing in Mexico and Texas. A recently started project at the Community First! Village in Austin will build 100 homes for the homeless. The University of Maine’s Advanced Structures and Composites Center (ASCC) is also about to start work on a nine-home neighbourhood for the homeless, exploiting a convergent manufacturing process involving factory-based 3D printing.

As governments worldwide struggle to deliver quality homes in sufficient numbers using existing approaches, they are increasingly turning to advanced construction technologies, such as panellised or module off-site prefab and 3D printing.

Analysis by Heriot-Watt University in 2018 identified the need for 90,000 new homes for social rent in England each year up to 2031, yet in 2021/22 only around 7,500 were supplied. Last year, housing associations in England cut their planned spending on new affordable homes by 9 per cent.

In last year's US presidential election, housing affordability emerged as a key issue with a survey finding that 69 per cent of Americans were 'very concerned' about the cost of housing.

Proponents of 3DCP claim it can deliver significant cost savings thanks to speedier construction, reduced on-site labour and reduced waste.

The Accrington development aims to reduce waste by 60 per cent. Its mobile printer, supplied by France-based Constructions-3D, only adds materials where they are needed, layer by layer. The printer is positioned on the floor plate and prints the walls from inside the building.

The three social housing units in Dundalk were constructed using COBOD’s gantry-mounted BOD2 concrete printer, which piped out a specialised concrete formula to match a digital plan.

Printing the cavity walls, instead of using bricks and concrete blocks, took just 12 days and, says COBOD, enabled the project to be completed 35 per cent faster than if using conventional methods – in 132 days rather than 200.

Around half of the time savings came directly from 3D printing the load-bearing double cavity system; the rest from the precision of 3D construction, which allowed for the seamless integration of components, such as partition walls, floor systems and trusses.

COBOD International's founder Henrik Lund-Nielsen tells RIBAJ: 'In conventional construction, one or two centimetres of deviance is normal, but here we are talking mere millimetres of deviance between what it should be and how it is. It means you can save a lot of time.’

The 10cm-thick walls do not require any conventional reinforcement and were printed in compliance with both EN206, Eurocode 6 for unreinforced masonry construction and ISO/ASTM 52939:2023, the new international standard for additive manufacturing.

Aside from speed and precision, Lund-Nielsen points to the labour savings of 3D printing. However, he adds that cost benefits around reduced waste on site are only noticeable when scaling up to higher-rise schemes, where it’s possible to reduce the volume of concrete and reinforcement needed to meet structural requirements.

'On low-rise, where the structural forces are so limited, it's more difficult to find savings,' he says. 'You have to go five or six storeys.' To date, 3D printing projects in Europe have not been allowed to go this high.

House prices in the US have skyrocketed since the pandemic, and the combination of an ageing workforce and issues with hard-to-reach job sites has caused a significant labour shortage.

The University of Maine’s ASCC aims to tackle these two issues with a new composite manufacturing process involving what’s thought to be the world’s largest polymer 3D printer, designed so that fewer people can build more homes.

All the elements for a prototype 600 sq ft (56m²) single-family home, including the floor, roof and walls, were printed at ASCC’s factory using a unique extruded waste material made from locally sourced wood fibre and bio-resin, before being transported to site.

In an effort to scale up the process, the university has invested in a new ‘research factory of the future’, which this year will begin printing a development of nine homes for the homeless. It aims to make the process cost-competitive with regular stick-built construction.

According to ASCC executive director Habib Dagher, using sustainably sourced waste wood and bio-based resins to print the homes will significantly lower the cost of construction and provide benefits for the environment.

'We have a sustainable source of biomass, and these homes allow us to lock in carbon, creating carbon storage and sequestration units,' he tells RIBAJ.

The university’s gantry-mounted printer is able to print elements up to 18m long, 6.7m wide and 3.4m high, and the end effector can be switched to perform processes that include 3D printing, continuous fibre tape laying, ‘pick up and place’ operations and other machining and robotics.

The multi-use system was devised, says Dagher, to overcome the challenges associated with regular concrete printing, whereby 'you print the walls, but you still have to put the roof together, do the electrics and insulation and finish the home on the inside'. These involve 'a lot more labour processes on site, which drives up costs and slows things down'.

Additive manufacturing, as with other technologies conceived to increase automation, has serious implications for a range of skilled and unskilled workers employed in construction, from bricklayers and carpenters to architects and engineers.

Some have raised concerns about the technology’s suitability for building homes. James Rose, director of the Institute for Smart Structures at the University of Tennessee, says most commercial 3D-printed housing projects in the US are being delivered in concrete – 'a carbon and water-intensive material which, due to its weight, currently makes it difficult to print overhead enclosures'.

Other materials seem to offer more flexibility, says Rose. 'The architects Ron Rael in the US and Mario Cucinella in Italy are experimenting with site-sourced clay, which holds promise for carbon reduction, offers lower cost, and has proved to be adaptable to complex vaulted enclosures.'

Paul Shepherd, deputy director of the Digital, Manufacturing & Design Research Centre at the University of Bath, says additive manufacturing is great if you want to build something in a complicated shape that can be built up in layers, but asks: 'How many low-cost refugee houses need an architectural expression of a curved wall when you can quickly make them using flat elements?'

Shepherd was principal investigator on a Bath research project to robot-manufacture a ‘thin shell’ concrete vaulted floor slab with 60 per cent less embodied carbon than an equivalent flat slab. He claims the 'sweet spot' for 3D printing is in an off-site environment, rather than on site. 'You've got the control, you can ensure repetition and quality control, then ship pieces to site and bolt them together, rather than having to wait for things to set,' he says.

Lund-Nielsen counters that COBOD’s on-site approach offers benefits over precast because factory-made elements are typically over-engineered and contain too much reinforcement, for example including rebar used to lift panels from moulds onto trucks and then unloading them by crane. He says COBOD’s process only puts reinforcement into the columns, not the walls, and the volume of rebar is dictated by the height of the building.

'For ages, construction has made structures that are unsustainable, using too much reinforcement and too much concrete, which is because of the method of fabrication,' he says.

With global research efforts and real-life deployments of large-scale 3D printing accelerating, surely a conclusive answer on the technology’s long-term viability in construction can’t be far away.