On London’s ‘Silicon Roundabout’ Brookfield Multiplex is delivering the White Collar Factory – Derwent’s vision of a low-cost, energy-efficient office.
Client: Derwent London
Contract value: £98m
Main contractor: Multiplex
Structural engineer: AKT II
Structural engineer: Arup
Start date: August 2014
Completion date: August 2016
‘Silicon Roundabout’ on the City of London’s northern edge brands itself as the hip, happening hub of the UK’s tech start-up industry.
The Old Street gyratory, to give the traffic island its more formal name, is lauded as the world’s third largest technology start-up cluster after San Francisco and New York City, with businesses such as Google, Tweetdeck and LastFM all present in the area.
It is also where Derwent London is plotting a new, low-cost, energy-efficient approach to office space, which the developer believes will reflect the changing demands of workspace environments.
The White Collar Factory, which sits on the south-west corner of the roundabout, is a commercial office development being constructed by Brookfield Multiplex.
The 16-storey tower will be the feature building on a ‘campus’ known as Old Street Yard, with a construction cost of £98m.
All 237,000 sq ft of the tower will be commercial office space, while five low-rise buildings will provide a mix of offices, restaurants and residential, taking the total development up to 293,000 sq ft.
The name of the site, its minimalist design and ambitious environmental targets are all intended to appeal to businesses that want to base themselves in the local ‘flat white economy’ – the moniker given to a collection of media, internet and creative businesses driving growth in east London.
Confident market speculation
It is a speculative development, such is Derwent’s confidence in the approach.
“We have deliberately designed a building which was flexible and attractive to creative tenants”
Matt Massey, Derwent
“We see office space going this way, with more flexible workspace occupied by high-tech tenants typical of Silicon Roundabout,” says Derwent senior project manager Matt Massey.
“We have deliberately designed a building which was flexible and attractive to creative tenants.”
The building’s location on the noisy Old Street roundabout might give prospective tenants cause for concern.
But Mr Massey is quick to reassure: “The design team took into account the levels of noise and pollution and even on lower floors it is negligible.”
The construction cost is below the BCO (British Council of Offices) average of £180 per sq ft, and Derwent expects the building’s energy running costs will be 15 per cent lower than a typical new-build office. The target rent is £55 per sq ft.
The location of the development on the Old Street roundabout has presented Mr Sinclair’s construction team with plenty of logistical issues.
“It is an island site, surrounded by roads, and there is a one-way system at the back of the site that stopped us carrying out road closures,” he explains.
“The nearest holding zones for trucks are a mile away in Hackney. There is limited storage on site, so the trucks are called in as we need them.
“The M&E plant had to be brought in early and stored in the basement after it had been constructed, because otherwise we would have had access issues bringing it to site.”
The whole site is what Derwent calls a ‘lifecycle product’, as Mr Massey explains.
“The low-rise buildings have ‘incubator office space’ and as these companies evolve and become bigger and need more room, they can take space elsewhere in the development.”
The design of the tower aims to create large, flexible, open-plan work space with exposed services and structure.
It is inspired by mid-20th century French architect Jean Prouvé, who introduced manufacturing technology into architectural design, and has a bare, stripped-back, industrial feel – but with 21st century technology.
In another nod to Prouvé – who was originally a metal worker – the building’s exterior uses glazing interspersed with anodised aluminium punched with round ‘portholes’.
Internally, the clear floor-to-ceiling height is 3.5 m, which includes a 200 mm-high raised access floor for electrical services and ICT, including a fibre optic ‘spine’.
The structural floorplate is set out on a 9 m x 9 m grid, with cladding modules at 1.5 m intervals – a layout that aims to make it easy for tenants to subdivide according to their requirements.
It is a concrete structure, much of which is exposed. A ‘board mark’ finish – achieved from carefully selected timber shuttering – is being used for feature walls in reception, the ground floor external walls and the walls of the lift lobbies.
Smart environmental techniques
As well as being a design feature, the concrete structure also includes the development’s chief environmental innovation.
“Chilled or heated water pumped through the pipes will keep the internal ambient temperature at 24 degrees centigrade in the cooling mode or over 20 degrees centigrade in the heating mode”
Matthew Sinclair, Brookfield Multiplex
Brookfield Multiplex project leader Matthew Sinclair explains: “The reinforced concrete slabs include a cooling system, in the form of a network of embedded pipes.
“Chilled or heated water pumped through the pipes will keep the internal ambient temperature at 24 deg C in the cooling mode or over 20 deg C in the heating mode.
“This eliminates the need for air conditioning and reduces the volume of plant required.”
Prior to construction, Brookfield Multiplex built a full working prototype on site of a typical floorplate section, with in-slab cooling, to prove the concept would work.
“Based on the typical energy use of the office building, the temperature will rise to the 24 deg C, which is considered a comfortable working temperature,” Mr Sinclair says.
What M&E plant there is will be in the basement and on the roof. There is also a green and brown roof, plus a running track around the perimeter of the tower roof.
Below the low-rise buildings is a double-level basement, used for plant, cycle storage and showers, while under the courtyard sits a double-height basement that can be used as an auditorium or cafe.
Traffic light cooling
Besides the concrete cooling system, careful thought has gone into the rest of the environmental design.
The double-glazed glass has U-values of 1.2 W/sq mK and adapts to solar conditions, preventing excessive heat transfer.
“The windows are openable and there will be a traffic light system on each floor to guide occupants on when to have the windows open and when to close them depending on the outside temperature: green for open, red for closed,” Mr Sinclair says.
The concrete includes cement replacement to boost its green credentials and achieve the different shades of grey desired by the architect.
“To achieve that without using pigments, we have used pulverised fuel ash (darker) and ground granulated blastfurnace slag (lighter),” Mr Sinclair explains.
“There is 200 kg per cu m of PFA and it is 30 per cent GGBS. This was achieved through 12 months of concrete sampling with suppliers to come up with the optimum colours.
“There is currently a shortage of PFA on the market due to reduction in coal-fired power plants, so we had to secure the supply through placing advance orders.
“During the design phase, we also carried out extensive tests on striking times because of concern over the curing time of concrete with cement replacement in cold weather.
“Normally, you would expect a strike time of inside a day; in this case, we had to leave it for 48 hours.”
The timber on the project is FSC-certified and 95 per cent of the steel is recycled. Embodied carbon is also being monitored.
“We will use the Environment Agency embodied carbon tool and a bespoke tool created by BRE, and we benchmark against the industry average,” Mr Sinclair notes.
Renewable features include 300 sq m of photovoltaics and 100 sq m of solar thermal.
Brookfield Multiplex is targeting BREEAM Excellent 2014 for the scheme. “Contractually it is BREEAM Excellent 2011, but having looked at the 2014 requirements, we think we are on the way there based on the design work done already,” Mr Sinclair says.
The project workforce’s peaking this summer at around 350 as the superstructure takes shape.
Brookfield Multiplex’s team on the White Collar Factory has a high female contingent, with 40 per cent of its personnel being women.
With final completion scheduled for summer 2016, the team will soon be putting the finishing touches to what Derwent hopes will house the next generation of London’s flat-white brigade.
The most interesting construction challenge for Mr Sinclair’s team concerns the basement and foundations, particularly on the north side of the site where the base of the main concrete core sits.
“For the main core construction, we came up with a sheet-piled cofferdam solution,” Mr Sinclair explains.
“Due to the proximity of the national rail tunnel and the London Underground tunnels (which run between Old Street and Moorgate stations), we decided sheet piles were the best solution.
“This enabled the bulk excavation of the main core to commence early while piling was still being carried out on the site.
“Around the main core, 15 plunge columns were cast into the piles, which allowed the ground-floor slab to be cast on top of the piling mat.
“Once the ground floor was completed and locked into the capping beams on top of the piles, bulk excavation was carried out under the ground floor to allow the two levels of basement to be constructed, while we continued working on the superstructure above.”
The piles range in depth from 30 m to 35 m and 1.2 m to 2.4 m in diameter. In total, 95 piles are being used with a total length of 2.9 km.