East side story: proving the potential of volumetric construction

A project in Walthamstow is proving just how far volumetric modular construction can go, with 75 per cent of two new towers being built offsite

In its latest report, the House of Lords’ Built Environment Committee criticised a lack of progress in the UK’s adoption of modern methods of construction (MMC), arguing that the sector lacks coherent government support and measurable objectives.

High-profile failures in the past two years suggest pitfalls in the MMC business model, but with the right approach from the public and private sectors, there is no reason why modular solutions can’t play their part in solving the UK’s housing crisis.

In Walthamstow, for example, specialist modular contractor Tide Construction is using a volumetric approach to build phase one of The Mall, comprising 495 build-to-rent flats, for client Long Harbour, which acquired the site from real estate investment trust Capital & Regional (C&R) in December 2020. Selborne One and Selborne Two – a pair of now-dormant C&R subsidiaries – obtained planning permission in January 2021 for a two-phased redevelopment of the site. Phase one’s construction of two residential towers will be followed by the expansion of the existing 17&Central shopping centre in phase two, for which C&R hasn’t yet chosen a contractor. Together, both phases will occupy a 2,700 square metre footprint.

Tower A rises 34 storeys and 116 metres while its neighbouring Tower B is 27 storeys at 92 metres. They will contain a combined 1,375 modules once completed: a mix of bedrooms, bathrooms, kitchens and living rooms manufactured in Bedford by Tide’s offsite subsidiary Vision Modular Systems (VMS). Some 75 per cent of the project will be constructed offsite, but not only by VMS. The communal staircases, for example, are being made by Peterborough-based Stair Master.

Tide is no stranger to the volumetric scene. It claims to have constructed seven of the 10 tallest modular buildings in the world, its highest being College Road in Croydon (163 metres, completed last year). However, the Walthamstow scheme is the first modular project commissioned by Long Harbour, which awarded Tide a £165m contract
in July 2022.

“If you came here two years ago, this site was just a yard with old retail units, some bins and not much else,” says Tide project director Richard Kennedy. Embassy Demolition Contractors worked for Tide in an enabling works package, which included foundation and piling works plus the separation of services between the live shopping centre and the phase one site.

Tower B sits above a Tube line, so Tide needed design-stage engagement and approval from Transport for London before piling subcontractor Murphy Ground Engineering was free to drive a total of 240 piles into the ground to an average depth of 28 metres. Murphy used a continuous flight-auger piling technique, says Karl Roulstone, the firm’s preconstruction lead. With piling work completed, Tide built the cores for both blocks above basement level.

Onsite activities included batching and pouring of the reinforced concrete (RC) centralised core shaft and frame for each building, carried out by groundworks and RC contractor OBR Construction under a £9m subcontract. The frame functions as a transfer structure to redirect the vertical loads. It goes up to the third storey on each building and the core rises above it.

Before implementing the RC frame, OBR also conducted groundworks such as underground drainage, underground services, waterproofing and foundations. The slipformed core for each building was implemented at a typical tempo of a floor a day, or 34 days of pouring for Tower A and 27 for Tower B. “On a typical day, we had 10 concrete wagons arrive on site when we were pouring the core,” says Kennedy. Each wagon contained 7.5 cubic metres, meaning 75 cubic metres of concrete was poured per day.

Fast timetable

Tide is delivering modules at a steady pace and to a fast timetable, with all flats set to be installed within a 21-week window that opened in September 2023. The contractor calculates that a traditional construction approach would have taken 98 weeks. “On each floor in both buildings there are 25 modules,” says Tide and VMS chief executive Christy Hayes. “Each week we install 65 modules. That’s the equivalent of two-and-a-half floors per week.”

Kennedy says all volumetric units are watertight before leaving the factory, including rainscreen cladding for the external walls. “The modules come with the internal wall already installed,” he adds. Once on site, the units are craned into place and stacked vertically on top of the frame and around the RC core in each tower. Tide then completes the final connections, commissioning and external, non-combustible facade system, including all fire-barrier compartmentation.

Steel connectors link the modules vertically and laterally at specific points to one another and to the RC core for structural stability and minimal differential movement. Tide construction director Darren Twomey says: “We cast plates when we were building the concrete core that tie each module horizontally onto the core when it’s lifted into place.”

Site logistics could have posed a headache, as The Mall is sandwiched between a rail line to the south over a busy main road, and the shopping centre directly to the north. In addition, Walthamstow Central station is just 160 metres to the east. But the volumetric method scores big for logistical efficiency. Each module is transported almost 50 miles by road from the VMS factory in Bedford to the roadside next to the two under-construction towers. “All we need to install modules is a parking bay,” says Kennedy.

On its visit, Construction News witnesses the process in action. A module (in this instance a fully fitted kitchen) arrives on a flatbed truck, is picked up by one of two tower cranes provided by Laing O’Rourke subsidiary Select Plant Hire. The 12-metre-high cranes are installed atop the central structural core on each building, and modules are lowered into place in 10-15 minutes.

Twomey says Tide created a detailed cranage strategy for the project that includes a VMS-designed lifting frame that prevents the cranes from obstruction as they place the modules. “Each volumetric unit has designated lifting points that allow the unit to be safely lifted [from the roadside] and installed with precision tolerances,” he notes.

The modular units weigh an average of 20 tonnes and arrive onsite with 80 per cent of their interior fittings already in place. The cranes will remain onsite until all the modules are installed, and they will be removed after the VMS-manufactured crown steelwork is installed on the roof of each tower.

The 3-metre-high modules come in various widths and lengths (up to 4.7 metres and 10.3 metres respectively). Their installation takes place with minimal human involvement, says Hayes, and this helps to reduce site safety risks compared with traditional methods. “You can imagine, if this was a traditional build, the number of deliveries and tradespeople involved.” He adds that traditional methods of construction for the two towers would require 450 to 500 site workers, whereas the onsite workforce is currently at peak activity with 110 staff.

Among the workers on site are staff from Century Facades, who are installing cladding rails and glazed terracotta cladding on Tower A, working on the facade from double-stacked mast climber platforms. The terracotta material is made in Germany by NBK. Aluminium-framed windows from Reynaers are installed offsite by Century.

Backbone mechanical, electrical and plumbing (MEP) works are provided by specialists from Red Group. There are fewer onsite MEP requirements than with a conventional build, as the modules arrive with lighting, pipework, sockets and even electric appliances pre-installed in the factory. “Once installed, the MEP within the volumetric units is connected and commissioned to the central MEP within the building,” Twomey explains. He adds that the overall production, delivery and installation process means the project is on course for handover to the client in March 2025, three months ahead of schedule – rare for a construction job.

Asked why more firms can’t implement rapid-tempo projects, Hayes comments that the “vertically integrated” nature of Tide helps to ensure a smooth construction process. “We’re developers, contractors and offsite manufacturers,” he says. “I think maybe where [other] models fail is where the main contractor and modular supplier are different companies and may not understand totally how the whole building comes together.”

So how far can offsite construction go? “You’ll always have to do certain things on site: the foundations, roofing, lifts, and a certain amount of backbone MEP,” says Hayes. “But I think we can get to a position [in future schemes] where we can peak at around 95 per cent offsite manufacturing.”