Why steel is the original offsite construction product
The government is currently pushing for increased use of offsite manufacturing in construction – but the steel sector has long been using factory processes to deliver efficiency gains, says Sarah McCann-Bartlett.
The government and the Construction Leadership Council have earmarked offsite manufacturing as a route to increase industry productivity and reduce costs. Steel framing is the original offsite product and has long been delivering advantages to clients.
Today, fabrication of individual steel pieces takes place under controlled, highly regulated and safe factory conditions, where the use of digital design and leading-edge fabrication systems deliver precision-engineered components with minimum waste.
Steel components can be further pre-assembled or fabricated into modules, either in the factory or at the site. Structures are often prototyped or “trial built” offsite to ensure a perfect fit when the modules undergo final assembly on site.
Constructional steelwork firms also work closely with other specialists in the supply chain, notably building services, to allow other elements of the build to take place off site.
For example, steel contractors working on motorway gantries receive designs from Highways England that have the M&E incorporated into the BIM model. The steelwork firm fabricates the gantry in its factory, and then in the same manufacturing facility the M&E contractor incorporates the electrical and communications cabling and junction boxes on the gantry bodies.
The steelwork contractor transports these gantries to site where each one is typically installed in just 30 minutes. Signage and lights are fitted once the gantries are erected.
“Fabrication of individual steel pieces takes place under controlled, highly regulated and safe factory conditions, where the use of digital design and leading-edge fabrication systems deliver precision-engineered components.”
On the north core of the Leadenhall Building in London, steel specialist Severfield prefabricated ‘table’ units incorporating building services components and precast floors. The steelwork contractor fabricated the units, which were then moved to another factory and fitted with the M&E components and precast floors before being brought to site.
Three “tables” were installed per level, and the passenger and goods lifts structures were hung off the units on either side.
The same firm prefabricated 1,200 steel cassettes for the London Bridge Station redevelopment, each one a bespoke unit due to the changing rooftop geometry.
These 9m deep by 3m wide cassettes were assembled at Severfield’s Bolton factory, then the project’s M&E contractor installed the services and the cladding contractor formed each cassette’s canopy roof. Each 2.5 tonne unit was lifted into place by tower crane.
The benefits delivered by steel’s offsite processes are aligned with the government’s ambitions for the wider construction sector. In a post-Brexit economy, they also mitigate key risks.
A faster onsite programme means government construction targets can be met more easily, as the work is less affected by adverse weather, while a shorter onsite programme is more cost effective. Fewer people are required on site which helps to mitigate issues around skills shortages.
Onsite safety is improved as the need to work at height is reduced. The controlled offsite environment ensures consistency and reliable quality.
Additionally, the adoption of automation – and now robotics – plus digital design for manufacture and assembly, including full Level 2 BIM uptake by steel fabricators, has created new skills in the sector.
The stable long-term nature of jobs in a steel fabrication factory assists in training a specialist workforce, while manufacturing employment brings stability and growth to communities that might not benefit directly from investment in construction or infrastructure projects.
Sarah McCann-Bartlett is director general of the British Constructional Steelwork Association