Prefab redux

Atkins | 02 Jun 2016 | Comments

From housing to schools to military bases, offsite construction methods are opening up a realm of new possibilities in building design.

Using offsite construction building methods and modes isn’t anything new. Prefabs have been a feature of construction projects for years.

But for designers, engineers and planners, the possibilities that offsite construction methods and materials can offer have begun to present genuine, lasting and cost-effective solutions to some seemingly intractable problems: housing shortages in areas of high population density; the need to update dilapidated school stock in these straitened times; and delivering robust buildings for engineering and military projects, often in hostile environments.

But what exactly do we mean by ‘prefab’ in 2016? In practice, the term covers a wider range of techniques than simple boxes.

The first is template, where the form of the building is predetermined and a client effectively buys off plan to a pre-designed solution. This is typified by the Sunesis range of designs, which Atkins has produced for the Keynes primary school range. Through this approach, schools were pre-designed, allowing school leaders to choose the configuration of classrooms based on a standard template. This was then delivered within a shortened timescale.

The second type is volumetric, where a building is made using pre-formed box volumes of space that are constructed off site and assembled on site.

The final system, kit of parts, has nuances but generally relies on creating rules for designers that define aspects such as structural dimensions, the number of components and certain limitations on how these can be assembled. “This is typified by solutions that Atkins has developed alongside major contractors such as Laing O'Rourke,” says John Edwards, associate architect at Atkins in the UK. “This approach potentially gives the greatest flexibility to clients and designers alike.”

Modular learning

Over the last few years, Edwards has led a number of projects where offsite construction has allowed engineers to deliver solutions faster, cheaper and with less environmental impact.

So far, much of his work has centred on schools, where there is a pressing need for cost-effective solutions to address a lack of space. “The desperate need for new school places has only partially been addressed,” he says, explaining that the shortfall cannot be met entirely with new, traditionally built schools. Refurbishing schools, as well as extending existing facilities, can deliver results quickly.

“Authorities are looking at a school campus from this point of view and considering extending certain buildings because they have a rise in the number of primary school pupils,” he adds.

Given the possible demographic shifts that can take place within certain areas, the benefits of a modular school constructed offsite are even more marked. “The clever thing would be if you could move that building, once it was no longer needed, back to the factory and re-service it for future use elsewhere,” says Edwards. “That’s when you start looking at things that don’t have foundations or have very minimal ones.”

And while a significant benefit of offsite construction focuses on standardisation – reducing cost and time – Edwards is at pains to emphasise other, less obvious angles. “Rather than being obsessed with this word ‘standardisation’, we should be looking at innovation and creativity,” he says.

“For instance, using new technology and data, we are beginning to use our understanding of light to inform how we design and create spaces for the end user. This also helps us to reduce reliance on complicated mechanical and electrical systems, and environmental impacts and running costs.”

Edwards’ pioneering projects have already delivered tangible benefits. New buildings show improvements in the use of recyclable material, reduced waste, optimised durability over the course of the building’s lifespan, and lower water and energy use – both during construction and while the building is in regular use.

One of the more striking examples of this approach can be seen at the new Lime Tree Primary School, south of Manchester, which was designed using the Select modular assembly system – a unique hybrid steel and precast concrete volumetric system pioneered by Laing O’Rourke. The solution cuts down the amount of on-site labour required as well as reducing cost and materials used.  

At Lime Tree, the 1,650m2 build, designed to accommodate 420 pupils, was delivered in just 19 weeks, and encapsulates how offsite construction techniques, coupled with traditional schemes, can help schools nationally meet increasing demographic demands.

The bespoke design for a ‘forest’ school gives Lime Tree a highly specialised environment that prioritises outdoor learning and direct engagement with nature. Off-site construction kept time on site to a minimum – allowing the whole project to be delivered over the course of a summer holiday – while the ability to design the school to specific needs makes it a genuinely distinctive learning environment.

Military missions

It’s not only school building that lends itself to offsite construction. This approach offers a solution for any setting where the use of heavy materials may present a problem or where project duration has to be curtailed. One such arena that is increasingly turning to offsite construction is the military.

From Afghanistan to the Horn of Africa, the need for sturdy military buildings has grown exponentially in the last decade. This is partly explained by the changing nature of military strategy; more and more operations are relatively ‘light footprint’ – with rapid reaction forces and a more agile approach increasingly favoured over a longer-term focus on the occupation of territory.

As Terry Suehr, director, project management excellence at Atkins in Virginia, US, explains, the main challenge in the military sphere has been to build high spec, durable structures in hostile environments, under immense time pressure.

Suehr led the project to design and build comprehensive architectural engineering services for 10 two-storey modular barracks at two separate project sites at Bagram Airfield, the US military base in Afghanistan.

The relocatable buildings (RLBs) – which are fondly referred to as ‘man in a can’ by the military – contained 36 containerised living units (CLU) each. Six RLBs are located at the Bagram Theater Internment Facility project site, and four at the nearby Ronco site.

Shipping containers were repurposed for use as housing facilities, with one living unit per container, all opening to the exterior. The barracks represented a successful attempt to find a middle ground between temporary tent-based accommodation and a permanent structure. Sturdy and easily assembled, the units were also designed to be relocatable, as and when the end of the mission arrived and a new need was identified.

“All of the exterior walkways and stairs were bolted in place so you could disassemble them and move the facilities if required,” says Suehr, who stresses the importance of designing a simple facility that enabled regular maintenance following the departure of skilled engineers. That was especially true at Camp Lemonnier, the project on which Suehr advised in Djibouti.

“You don’t have the skilled labour, so there are a lot of challenges with that,” she says, recalling the work required to build an air base for the Japanese military, which needed a more permanent structure from which to co-ordinate its anti-piracy mission.

“In Djibouti, like Afghanistan, it really affected the way we designed. We had to understand the skill levels of the labourers and change a lot of our designs accordingly. We could never use welding, for instance.”

The Atkins team worked with construction partners who knew the skill levels of the local labour force. “There was a tremendous amount of collaboration back and forth,” says Suehr. “We’d go through the specifications and the way we were going to design them, and our partners would give us feedback and say, ‘No, I don’t have labourers who know how to do that. I need you to design it this way instead’”.  

She adds: “Initially the operators of these facilities would have been Americans, but at some point, they were handing them over to the Afghans or other local forces, like the water treatment plants and storage facilities and waste water storage. We had to make all the equipment and systems very simple, very maintainable and able to withstand the harsh conditions. We couldn’t use the technologies common in the US.”

Through adapting designs off site, the Atkins team could create units that were constructed offsite and fit for purpose – portable, durable, cost effective, easily assembled and maintained.

Connected cities

Beyond the temporary fixes of war zones, offsite modular construction is also playing a significant part in the long-term development of cities. One project, New Islington in Manchester, even allows residents to help design their new homes, which are then assembled on site.

And far beyond the UK, advanced offsite construction schemes are already taking shape. Take the Chinese desert city of Karamay in the isolated province of Xinjinag Uygur, north west China, for example.

Its origins as an oil city can be seen in the grime on its oldest structures but in recent years, provincial authorities decided that Karamay needed to take the next, belated step in its own development: to become a vibrant, varied city that attracts new immigrants and offers a broader range of social, economic and cultural resources. Central to this has been the construction of the Karamay Cloud Computing Industry Park, the centrepiece of the new Karamay economy.

Karamay’s climate is harsh – bitterly cold in winter and scorching in summer – making long-term construction difficult. Finding the right skills and materials to build from the ground up was a major challenge, both logistically and financially.

In terms of engineering complexity, it is relatively easy to create a business park, but Karamay was different because the design had to be more modular to allow construction off site. The buildings were linked, like pods, and had to be relatively lightweight, so as to be built easily off site, transported and then bolted together.

This allowed engineers to create a network of linked offices. This is particularly useful in winter, as it allows people to move between them without having to go outside and face the ice, snow and wind.

From the desert plains of Afghanistan to a densely populated suburb of a large city in the UK, offsite construction techniques are helping more and more sustainable solutions to take shape. The only question now is, what’s next?