Offsite construction methods are supposed to offer significant gains on build quality – but is there evidence to prove it? Neil Gerrard investigates.
Offsite construction has long claimed an array of advantages over traditional build methods – speed of installation, fewer site workers and, perhaps most importantly of all, a higher quality finished product.
But not many clients see it this way. This was a problem raised by Laing O’Rourke’s technical director, Dr Sarah Williamson, when she gave evidence to the House of Lords Science and Technology Committee as it prepared its now-published report (see box) into offsite construction.
While Williamson praised an “enlightened” few private clients who were starting to see the benefits of offsite construction methods, she warned that gaining traction in other areas was proving difficult.
“The barriers [to offsite uptake] are to do with a perception issue,” she told peers. “Rather than seeing the benefits in terms of consistency of product, reliability of programme, reduced reliance on the traditional construction skills, what comes across is an increased upfront cost and perhaps in many areas a quality perception.
“People have in their minds the 1960s and 1970s builds post the Second World War which are not at all like the componentised offering of offsite construction that we see today.”
Proving that the quality of offsite construction is better than the results achieved through traditional methods is going to be crucial. So where is the evidence to prove it?
“There are quite a lot of published figures on poor quality when it comes to normal construction,” says Tim Carey, national product director at Willmott Dixon. “What doesn’t exist to the best of my knowledge, is anything linking that up with offsite. Gut feeling tells us that if you build stuff in controlled conditions with specially trained people then you are going to get better outcomes, but there is no measurable data I can find that proves that.”
Willmott Dixon, along with several other contractors plus construction research body CIRIA, is on a mission to prove offsite’s quality credentials in a new research study.
A spokesperson for CIRIA declined to reveal which other contractors are involved in the project but confirmed that its work will examine common project drivers in more detail, as well as identifying the benefits of offsite techniques against more traditional approaches by collecting data in a format that will enable comparison.
The outcomes of the research are expected to be published in 2019.
At the same time, industry body Buildoffsite is working with BSI to examine gaps in coverage for offsite build methods and whether there is the need for additional standards. The organisation hopes that in doing so, it can drive market demand. Any standards that are created are expected to be performance driven.
Anecdotally, construction professionals who have worked on offsite projects praise its quality performance.
“The theory of building inside a factory environment, which is warm, dry, windless, safe and under close supervision leads to the typical conclusion that we would end up with a better-quality outcome,” says Peter Flint, chief executive buildings + places EMIA at Aecom, which is planning a factory for 3,000 modular homes at Silvertown Quays in east London, though the scheme has stalled recently.
“The defect issue is massively reduced,” continues Flint. “I haven’t got any numbers to confirm that, but a very strong conviction and it is one of the biggest excitements for us.”
Cutting down on defects
Flint says the emergence of digital design tools have led to more “love” for offsite methods. “We design to 1:1 detail in the 3D environment and then we order from the supply chain from that 3D model so everything coming out of our workshops is built to the right tolerances and dimensions,” he explains.
That level of precision allows Aecom to cut down massively on defects as compared to traditional building, Flint asserts. “From a traditional project perspective, where hitting practical completion and getting defect free can be somewhat of a challenge, we are achieving most of that before it even leaves the factory,” he says.
Keith Blanshard, the former Yorkon boss who has worked in the offsite sector for 40 years and is now Buildoffsite’s executive director, is in no doubt that the quality of offsite work is superior.
“To watch a man on the line install insulation or tile a wall, it is just significantly better,” he says. “Putting aside for the moment the productivity gain, he is in a dry, clean environment and it generates a better quality finish. I come from a site background and you just know that on site you lose control of what is being covered up.”
But new skills will have to be learned, he points out. “I think there is a challenge for site management and project management on sites where they need to learn how to assemble a building,” he says. “How do you lift a 12-tonne module? You have got 15m of cable tray and pipes all tested, insulated and labelled up – that needs to go to the third floor, so how do you do that? Site managers need to pick these skills up, but they aren’t difficult to learn.”
A quality inspector’s view of offsite construction
Tony Mobbs, managing director of clerk of works consultancy Hickton, has seen the offsite industry evolve over 25 years of keeping tabs on standards in the sector.
While it is much better than it once was, continued inspection is vital, he argues.
“In the early days, there were as many defects in offsite construction as there were on traditional building sites,” he says. “Initially, going to a factory was like being on a construction site but it had a roof over it.
Tony Mobbs: Offsite manufacturers are now better
“We are now getting to a stage where the offsite manufacturers are better organised and more repetition is possible and this should lead to a better product. But I believe you have to have an inspection regime in place.
“On one visit to a particular factory, I found out that the intumescent seal to the junction of the walls and ceiling was not in place, therefore fire could get through at that point. The reason I was given was ‘oh, we had run out and the boss said we had to carry on’.”
Mobbs points out that car manufacturers’ plants he has visited, such as Toyota and Volvo, are fully automated and yet still have inspectors.
Nonetheless, he believes offsite construction can offer quality benefits if it is done correctly. “There are some good builders out there who can produce good quality buildings. But can onsite replicate that each time in the way that offsite is capable of doing? Offsite needs to be able to match the higher echelons of traditional construction and if it can, then are definitely gains to be made.”
The insurance sector’s view of offsite construction
Not everyone is convinced about the quality claims for offsite construction. Insurer Zurich, for one, has reservations.
Allison Whittington, head of housing at Zurich Municipal, says: “While we support the housebuilding sector’s ambition to embrace new and innovative methods of construction, we still harbour significant concerns around the adoption of Modern Methods of Construction (MMC), including offsite construction, where inappropriately used or not fully understood or supervised.
“Our concerns relate to the resilience of a finished development, including potential increased risk of larger-scale damage from flood, water damage and fire, as well as an increased risk to the wellbeing and possible displacement of the occupants. Likewise, combustible and lightweight materials such as wood, polystyrene and recycled materials have the potential to sustain a greater degree of damage than traditional materials, leading directly to an increase in repair costs and timescales.
Alison Whittington: concerns
“New standards and regulation are required to keep up with the fast-changing landscape of construction in the UK, but it is not good enough to simply suggest that regulation and design considerations should be able to mitigate these risks.”
However there is insurance backing for offsite technology. In a joint initiative, insurance firm BLP, Buildoffsite, the Royal Institution of Chartered Surveyors (RICS), and Lloyd’s Register have devised the Buildoffsite Property Assurance Scheme (BOPAS).
BOPAS provides assurance to the lending community that innovatively constructed properties will be durable enough to be saleable for a minimum of 60 years. The scheme involves a durability and maintenance assessment by BLP, as well as a process accreditation, and a web-enabled database comprising details of assessed building systems, registered sites and registered/warranted properties.
Earlier this year, BOPAS recorded a sharp spike in registrations of offsite manufactured construction products. Last year, the number of products accredited by the insurance body doubled to 20, with another 12 registered as of the end of May this year and a further 50 “in discussion”.
The Lords Science and Technology Committee report on offsite construction
The House of Lords Science and Technology Committee, in a report published this summer, argued that offsite manufacturing could help increase construction’s productivity, the quality and efficiency of buildings, while reducing labour demands and environmental impacts.
However, it warned that take-up has been varied and limited because the industry is working with outdated and unsustainable business models that are not conducive to offsite manufacture.
Offsite Manufacture for Construction: Building for Change sets out actions the committee thinks government should take, including “presumption in favour” of off-site manufacture and a greater move to procuring for whole-life value rather than lowest cost.
Willmott Dixon’s Tim Carey, who gave evidence to the committee, welcomes the report. But he warns that the mark of its success will be how the government and industry respond.
“A mere ‘presumption in favour’ is insufficient,” he adds. “We need government to define the parameters around the definition of presumption so that it very much is forced to become an opt-out that requires formal justification, as opposed to a soft opt-in.”