Europe’s tallest modular building yet, the 50-storey College Road residential scheme in Croydon, is Tide Construction’s second tower in the fast-growing borough, with over 1,700 units on a narrow, densely urban site. Stephen Cousins finds out how they did it.
Advances in Modern Methods of Construction (MMC) have fuelled a global trend for volumetric modular high-rise residential development, and nowhere is this more obvious than in the borough of Croydon in south London, where two of the world’s tallest modular buildings have been erected.
Marking the gateway to a new cultural quarter next to East Croydon railway station and reaching a height of 135 metres, Ten Degrees became the world’s tallest modular residential building when it was completed in 2021. The two interconnected 38- and 44-storey towers took contractor/developer Tide Construction and its volumetric manufacturer sister company Vision Volumetric just 26 months to deliver.
Fast forward to the end of 2023 and the same team was responsible for closing out an even taller 163 metre modular skyscraper on an adjacent plot, making it the tallest modular building (of any type) in Europe. College Road comprises one 50-storey tower with 817 co-living homes and amenity spaces, built for operator Outpost Management, connected to a 35-storey tower of 120 affordable homes.
Not just an offsite giant, College Road is also a pioneering co-living development, featuring an array of shared amenity spaces including a bespoke gym, private dining rooms, professional chefs’ kitchens, a library, a cinema, a spa, and a ‘sky garden’ – even a poker room and a podcast studio.
Taking volumetric modular to such unprecedented heights posed numerous design, fabrication and construction challenges for Tide and Vision Volumetric, architect HTA Design, and the wider consultant team. A limit on tower crane loading next to the busy railway required a rethink of module design; the high-altitude interaction of concrete cores and steel modules raised the spectre of differential settlement. Furthermore, the constrained urban site with a single access ramp demanded a meticulous plan for module delivery, storage and installation.
According to Ronan Farrell, head of design at Tide Construction, the procurement method used – and the vertically integrated delivery team – was a key factor in the project’s success; and also ticked boxes for the local council and the client. “We benefit from being the developer, the main contractor, and the offsite manufacturer,” he says. “That vertical integration gives us a huge amount of control over the procurement process and the delivery of the scheme, which in turn gives the local authority and our client quite a lot of comfort in terms of programme and cost.”
Historic references
The recent spate of high-rise development in Croydon is a contemporary echo of its construction boom in the 1950s and 60s, when a myriad of office blocks went up in the town as part of aspirational plans to create a new post-war society.
The architecture of College Road references that mid-century heritage and optimism; in particular, the faceted white terracotta cladding picks up on architect Richard Seifert’s iconic NLA building, also known as the ‘50p building,’ located nearby to the east.
The facade evolves subtly with height thanks to a varying configuration of ceramic tiles at the base, middle, and top of the tower. A street level colonnade doubles up as an artwork, London artist Adam Nathaniel Furman having covered it with some 14,000 ceramic tiles with glazes ranging from deep indigo blue to white at the top. Arranged in black ribbons that increase in width as they rise up the building, the windows fully encircle the tower near the top, to add emphasis to a prominent, faceted “crown.”
Among the many strategic factors supporting the case for the development, the building’s location on the outskirts of London within 100 metres of a train station with fast connections to Victoria, London Bridge, Gatwick Airport was a particular draw.
“When developing in central London, rents and build costs and certain red tape can make things onerous, so sites like this one in Croydon become much more attractive to a developer like us,” says Farrell. “The team was also familiar with the council’s processes and working methods, increasing our confidence that we could take forward another site, albeit under a different tenure, split between co-living accommodation and affordable housing.”
Advocates of co-living say it is a useful bulwark against widespread loneliness and isolation in big cities, and College Road is the first co-living asset class approved by the Greater London Authority (GLA) under the London Plan.
The policy requires developments to meet new design standards including space provision for communal kitchens, dining, laundry rooms, living rooms, internal and external space and cycle storage.
Outpost Management manages the co-living element of the scheme through its Enclave:Croydon unit, offering short term contracts to anyone from young professionals, to students to people moving between jobs or who want to check out an area before deciding to move there.
“Co-living is completely different from a normal rental situation where you’re often sharing a house or flat with several people,” says Rory Bergin, partner, sustainable futures at HTA Design, “College Road provides more private space – rooms are on average 22-24 m2, whereas in a typical Victorian house you’d be lucky to get 16 m2, with access to numerous communal spaces at a competitive rent.”
Narrow brownfield
The designers’ response to the site – a narrow piece of brownfield land accessible by a ramp being used as a car park below the surrounding street level – was to reduce the footprint to a minimum, creating two slender towers with a double-height colonnade wrapped around the base on the three public faces.
A new public realm and pedestrian route was created by cutting back the lower three floors of a typical floor plate, adding space for street greenery and encouraging access to ground level community spaces and a cafe.
The thin, tapering plot was a tricky proposition when developing the scheme’s massing, HTA chose to position the main frontage towards the railway and the narrowest elevation towards busy George Street to limit its visibility.
The extensive north-facing aspect limited scope for direct sunlight, so exaggerated folds were introduced in the facade to create triangulated oriel windows which introduce east and west sunlight into apartments.
Structurally, College Road is a hybrid, the basement, two circulation cores and the first four levels (housing key communal and amenity spaces), are built traditionally, in reinforced concrete. The top of the fourth floor acts as a transfer slab to support stacks of volumetric modules of different sizes and shapes above.
The volumetric design varies from floor to floor to ensure the most efficient use of steel as the load changes across the building’s height. Each module was delivered to site fully fitted-out and furnished.
“There are a variety of module types from one side of the building to the other,” says Bergin, “Most modules are different in plan, but because they stack vertically each module type is repeated across all floors.”
According to Tide’s Farrell, the structural system is very similar to that used on Ten Degrees, but there were certain “refinements to improve efficiencies.”
The sheer height of the building had implications for the alignment of the structure. Differential settlement can be an issue in taller buildings because concrete, in particular the cores, shrink at a greater rate than the steel structure.
A predetermined erection sequence was designed, based on detailed calculations carried out by Tide and the structural engineers, to ensure proper alignment during settlement. Furthermore, custom connectors were developed for the modules to slot into steel connection points cast into the concrete to allow vertical flexibility between the modules and the core.
Tandem lifts
The construction sequence saw modules manufactured in Tide’s factory in Bedford and delivered to site in batches while the concrete works were ongoing. The project was fortunate to have access to a large storage yard owned by the council just 150 metres away, so modules and materials could be dropped off overnight, avoiding daytime deliveries by road and the associated noise and access issues.
Two tower cranes positioned at the tops of the cores installed modules at a fast rate of 43 per week, equivalent to about one and a half floors.
Proximity to the railway line required crane lifting capacity to be ‘de-rated’ for safety, reducing the total weight they could carry. The largest module, fitted with bathrooms and kitchens, weighed
up to around 30 tonnes, including the lifting frame.
“When we were designing and modularising our building, we foresaw this de-rating as a potential issue and designed to accommodate it from the outset,” says Farrell.
As the stack of modules rose, the terracotta cladding system, made by Germany’s NBK Architectural Terracotta, was attached from mast climbing work platforms. There were two mast climbers per elevation, one to install the waterproofing and set up facade connections on the modules, the other following behind to fit the cladding.
The volumetric construction process, with parallel work streams on site and in the factory, had major benefits for the programme. The scheme was ultimately delivered in 28 months, two months ahead of the contract programme. Tide has estimated that even a 30 month timeframe would have resulted in a significant 40% time saving, compared to the equivalent traditional build.
As Bergin points out, speed of delivery can be a key deciding factor when clients are sizing up a residential scheme: “The sooner you complete, the sooner you can start bringing in rental income; if you finish a year or more quicker than a traditional building, that’s a year you can spend recouping some of the costs of the project,” he says.
Rapid construction wasn’t the only benefit, creating modules in a controlled factory environment where, Farrell notes, “each module was QA’ed five times, plus a final time by a QA manager” before it left the gate improves construction quality, “extending the longevity of the building.”
An approximate 60% reduction in labour onsite compared to a traditional build reduced workers’ exposure to high-risk activities, while the 300 factory staff all live locally, experiencing benefits for work/life balance. “The workforce is much more settled than on a traditional site, where people tend to be travelling longer distances to and from work each day. That’s a huge benefit; our staff retention is incredibly high,” says Farrell.
Advocates of MMC, including 3D volumetric, panellised systems and more, argue that it can play a key role in addressing the UK’s housing shortage, helping meet ambitious targets set by the Government. And while the offsite sector has taken a battering of late, with several large companies facing collapse and closure, the impressive state of high-rise construction in Croydon provides an encouraging example of what can be achieved when things work well.
To that end, Tide, Vision and HTA Design are collaborating on the design of another upcoming twin-tower volumetric scheme in the town, One Lansdowne Road, which gained planning permission at the end of last year.