It’s not just the usual features that make Arup Associates’ new building for Sky so sustainable – the huge timber frame cuts carbon use dramatically
When a building is assigned a catchy Americanised moniker, like Sky’s new ‘Believe In Better’ building in West London, it’s hard for us Brits not to grit our teeth and grumble. The likes of MacDonald’s and Nike might use aspirational slogans to try to sell us burgers and trainers, but surely not architects and engineers with their buildings?
The good news for the broadcaster is that the 3,850m2 new training and office facility, designed by Arup Associates, more than lives up to the positive branding. It is the UK’s first multi-storey timber commercial office block, manufactured offsite using a simple kit-of-parts approach that enabled massive savings in embodied carbon. Located on Sky’s huge campus in Osterley, which is home to more than 4,500 employees, the building was delivered in a scant 12 months from concept to ribbon cutting.
The building is a BIM exemplar, while airtight construction and energy efficient servicing, including mixed mode ventilation, air source heat pumps and advanced rainwater harvesting, have helped push it beyond carbon neutral status.
Mike Beaven, director and environmental engineer at Arup, says: ‘A key story with this building is its sophistication. It hasn’t been dumbed down to meet the rapid construction schedule; it does a lot with very few materials and systems. For example, we managed to eliminate all the metal ductwork, fan coils and other services at ceiling-level, while achieving very low energy use and a high fresh air component. It’s a low energy building, both operationally and in terms of embodied carbon: a symphony of components that work together in unison.’
The project began when Jeremy Darroch, CEO of Sky, asked Arup director Declan O’Carroll to design a new flexible temporary building for the site. The architect had designed the energy efficient Harlequin 1 Sky HQ on the campus, with its ambitious naturally-ventilated TV recording studios.
Darroch said he wanted the new building completed within a year, before the corporation’s 25th anniversary. But just four weeks after starting to develop the brief he changed tack and asked Arup for a permanent building, delivered within the same timeframe.
O’Carroll comments: ‘Sky is a very demanding client and can be incredibly challenging, but at the same time it is very supportive of doing innovative things, as long as you provide evidence of why they are worthwhile. The constraints of the programme led us to the pioneering use of an off-site manufactured timber frame and a very early procurement route.’
The Believe In Better building is multi-use and spread across three storeys. On the ground floor are educational facilities for the 50,000-60,000 school children that visit the campus each year as part of the corporation’s community outreach programme. The three floors above accommodate training facilities, used by 90% of Sky’s internal staff training across all disciplines, plus office and breakout space, and a restaurant.
Rectangular in plan, the building stands on the south side of a new plaza. Thematically, it was conceived as a glass-fronted ‘stage set’ where staff and visitors, ‘the actors’, can be seen from the plaza, the ‘auditorium’, wandering up and down a cascading social stair that stretches across the facade. ‘The stair is a unifying gesture, that links the three storeys and makes the building easy to navigate for users, many of whom will never have visited before,’ says O’Carroll.
The primary glulam timber frame is fully exposed and set out on a regular 6m by 8m grid, designed to enable super-flexible and adaptable interior uses. Floor plates adjacent to the main atrium provide break-out spaces that can be used as offices, or for training or informal meetings, while cellular technical training and teaching rooms placed along the south-facing rear elevation, can be expanded into double, triple or quadruple-size spaces, using special folding screens.
Glulam beams and columns, simply bolted together, form the timber structure, along with cross laminated timber (CLT) floor planks, and 2.5m wide, two storey high, prefabricated cladding cassettes that plug into the frame. The cassettes were delivered to site complete with preformed window openings, insulation, membranes, and internal plasterboard and, once installed, provide Passivhaus-level U-values.
Heavy reliance on timber accelerated the build programme, and eradicated the need for wet trades on site and their associated concrete setting times, reinforcement and formwork installation etc. Timber is also much lighter than precast concrete.
‘The idea was that building in very repetitive lorry-sized sections would be fast to deliver and erect,’ says Timothy Snelson, associate director and structural engineer at Arup. ‘A concentrated CLT core helps stabilise the structure and enabled the open plan layout.’
Thanks to carbon sequestration, the use of glulam and CLT, manufactured by Austrian supplier Binderholz, enabled a rock bottom embodied carbon measurement of -325kgCO2e/m2 for the superstructure. This compares to an estimated +150 for composite steel, +99 for concrete and -44 for a composite steel frame and CLT structure.
Timber massively helped offset embodied carbon in other building elements, such as the facade, foundations, services and finishes, leading to an overall score well below that of other sustainable buildings, says Snelson: ‘A decent sustainable building can deliver under about 350kgCO2e/m2, and anything below that is getting into green building territory. We ended up below -130kgCO2e/m2 – a complete step change for the industry.’
Cutting operational emissions was also key to overall energy performance. The building’s main picture window facade faces north, to minimise solar gain, and features a series of deep structural aluminium fins to increase solar shading. On the other facades, vertical strip windows with deep internal reveals restrict heat transfer and solar glare.
A mixed-mode ventilation system makes use of fan-assisted air supply plenums in the floor voids and intake louvres in the facades to draw warm buoyant air from perimeter spaces into the atrium and extract it at high level. An adiabatic cooling system sprays water over incoming air to provide energy-efficient cooling without using conventional chillers. At peak temperatures, this can be supplemented by DX coolers when the ventilation system switches from natural to artificial mode with heat recovery, and building occupants are asked to close windows.
‘The atrium stair encourages buoyancy, drawing air up towards the returns at roof level, and eradicating the need for return ductwork on each floor,’ says Beaven. ‘At the same time the building scavenges heat from pretty much everything: there’s no boiler and air source heat pumps continuously recover energy for heating and cooling.’
Partial user control of natural ventilation formed part of a WELL Building strategy for the facility – an Arup specialism for holistic sustainable design – intended to boost occupants’ physical and mental wellbeing by improving access to natural air and daylight, and improving levels of fitness and health.
Ann Marie Aguilar, associate director for wellbeing and sustainability at Arup, comments: ‘Sky’s corporate values are a major part of the vision behind the project. It emphasised a focus on sustainability, social engagement and creating a space where the employee and the occupant are strong elements in the overall programme.’
Renewable energy is supplied by a PV array on the roof, an on-site wind turbine, and a biomass combined heat and power system will be connected in the near future. Water use will be 63% less than in a conventional commercial office, owing to super-efficient washroom fittings and a pioneering FlowStow rainwater recovery system, designed by Arup, that channels unfiltered rainwater directly from a rooftop reservoir into toilet cisterns adapted to store rainwater.
‘Toilets on all floors flush using raw rainwater,’ says Beaven.’ The system is gravity-based and requires zero energy and zero pumping. If there is no rain for several weeks it can be supplemented with mains water.’
That such a complex integrated environmental system was achieved in a scant three month design period is hard to comprehend. Even so, this technical rigour should not detract from what is a very human piece of architecture, says O’Carroll: ‘The aim was to create a series of beautiful, dramatically different volumetric spaces. We built model after model to get the proportions right because we knew that the timber structure was the architecture, it was completely naked and exposed. As a result, the timber almost descales the building, giving it a sense of materiality, you see the warm texture of wood almost everywhere you look.’
It’s a positive message even the most cynical Brit can believe in.