Believe in Better Building, Osterley, London

Introduction

The Believe in Better Building, a new building for Sky on its Osterley campus, lives up to its name. It is the tallest commercial timber building in the UK and one of very few multi-storey timber offices in the world. Remarkably, it was designed and built in less than a year, starting on site only three months after Arup Associates’ design team was commissioned. It is an exemplar of sustainable design, achieving a BREEAM ‘Excellent’ rating, while the interior is an exemplar of World Green Council guidance on design for health and well-being of building occupants due to the quality of its environment. This is a unique and flexible workplace, constructed in half the usual time by the use of modern precision-engineered timber construction systems.

Sky’s brief specified a set of ‘super-flexible’ spaces which would accommodate the rapidly changing technology and working practices of the media industry. And these spaces had to go up at super speed – to be finished in time for Sky’s 25th anniversary in November 2014, then only a year away. To meet such a remarkably tight deadline, timber was the best choice; a structural frame of glulam timber beams and columns with cross-laminated timber (CLT) floor slabs could be prefabricated off-site and erected at speed while eliminating wet trades from the superstructure (CLT slabs can be installed at twice the rate of 
reinforced concrete slabs). By using large prefabricated panel timber cassettes to create the facades, a waterproof external envelope could be achieved early in the programme.

Timber offered other advantages: it is a sustainable, low-impact construction material with a surface finish which is warm, varied in colour and can be uniquely beautiful. The installation of a timber structure is generally less noisy than conventional wet construction, another important consideration when building at the centre of a working campus.

The building can accommodate up to 400 people and stands at the heart of Sky’s Osterley campus. Its three main floors are linked by a wide and open main staircase which rises through a triple-height atrium to a rooftop restaurant with an open terrace and great views. Externally the building makes a bold statement; the main staircase projects from the north façade in a series of dramatic inclines, fully glazed to reveal the activity inside.

The three floors were designed with no particular fixed use; instead, a series of internal room partitions slide and unfold to create a shifting landscape of creative thinking rooms, breakout spaces and informal meeting rooms.

A large open-plan space on the second floor can accommodate large meetings or gatherings and can be used just as easily for training or for large corporate events for up to 150 people. The ground floor is designed to house Sky’s Academy apprentice training and schools experience programmes. When not in use for this purpose, it can be transformed into offices or space for informal group meetings or creative activities. The floors are linked by the staircase; at first and second floors it widens and divides to create informal sitting and social spaces with views over the atrium and out to a newly created park-like plaza.

 

The design programme

The team started work on the project in October 2013; work on site began in January 2014 and the building was completed in October 2014, in time for Sky’s 25th anniversary in November 2014. Professional collaboration helped to achieve this. Arup Associates is a multi-disciplinary practice based on collaboration between architects and engineers; for this project the team of Mace, the contractor, moved into Arup Associates’ office for the three month design programme. Together they developed the design in parallel with procurement and construction strategies, before moving to site in January. From concept stage, key members of the supply chain, in particular B+K Structures, were part of the project team. Together they discussed how to optimise the speed of construction of both frame and envelope.

Arup Associates developed a BIM model of the building which was used for 3D BIM reviews with the contractor and designer during design and construction to coordinate the process. The model was also used as a ‘4D planning’ tool by main contractor Mace and was passed to B & K Structures so that they could begin to fabricate the glulam frame at the earliest opportunity.

The glulam frame was let on a reference design and performance specification (based on the principles of the new National Structural Timber Specification) to allow B+K Structures to optimise the final details for their fabrication and erection method. While Arup Associates worked on the final foundation designs, B+K Structures engaged structural engineer engenuiti to finalise the design and fabrication drawings, based on the Arup reference design. To avoid additional fit-out trades, B+K Structures installed the CLT risers and some fixed partitions at the same time as the frame was being erected.

 

The structure

The structural frame consists of glulam columns – generally 280 x 560mm - set between paired glulam beams, generally 260 x 920mm, bolted through with M24 bolts which were then plugged. The CLT floor slabs, generally 220mm thick, span between the beams and were fixed with Heco screws and brackets. Structural walls are limited to the stair cores, lifts and divisions between plant and public spaces. This is unusual, as CLT buildings usually rely on numerous load-bearing walls or stability cores with steel bracing or concrete walls. The exception is on the second floor where, to achieve a column-free space with unobstructed views for large meetings, a steel transfer truss is concealed in the wall of the plant room on the floor above.

Throughout the building interior, the glulam columns, beams and soffits of the CLT floor slabs are exposed, creating a warm and attractive surface.

A standard raised access floor system gives flexibility and accommodates the intense IT and MEP systems required by the media industry, together with air supply equipment. The raised floor provides a cavity between floor and slab which enhances acoustic separation between floors, so that no further acoustic treatment of the timber was required. As the main services are housed in the raised access floor cavity, there was no need for suspended ceilings and the timber soffits of the CLT slabs could be exposed.

The fire strategy was designed to avoid the need for sprinklers; the two cores are protected and have generous escape staircase widths.

The dramatic staircase which dominates the main, north façade is glazed with an innovative curtain wall system with external mullions which span up to 13 metres, creating a clean and minimal façade. Other parts of the external envelope were clad with prefabricated timber cassettes, pre-fitted with membranes and finished on site with anodised aluminium panels. They achieve Passivhaus U-values and levels of air-tightness.

 

Timber and sustainability

The glulam frame and CLT floor slabs, a unique structure of this size for a commercial building in the UK, achieves beyond zero embodied CO2 emissions (including carbon sequestered when the trees grow). All the structural elements are PEFC certified; the spruce glulam and spruce CLT were sourced from sustainably stewarded forests adjacent to the factories in Austria. The panel sizes were designed to be transported with maximum efficiency. All the timber components were manufactured with zero waste on site and any waste materials in production went to bio-mass CHP (combined heat and power), with the energy produced used to heat the factories.

The main staircase and its informal social spaces are lined with FSC® certified birch Plexwood, from managed forests in Sweden and Finland. Other joinery elements are made of FSC certified plywood. The handrails to the staircase and balustrades are of English oak.

The building has been a success; so much so that Sky has commissioned their next building, a health and fitness centre, to be built with similar timber construction techniques. A new office building, currently on site, has been altered to include timber breakout spaces and a timber roof, the largest in the UK.

Completion Date:

October 2014

Year Published:

October 2015

Building Type:

Commercial

Location:

Osterley, West London

Client:

BSkyB

Architect:

Arup Associates

Structural Engineer:

Arup Associates

Main Contractor:

Mace

Timber Contractor:

B+K Structures

Timber Supplier:

Rubner Holzbau (Glulam and cassettes), Binderholz (CLT)

Timber Engineer:

Engenuiti (stage E/F)

Timber Joinery:

Taylor Made Joinery

Timber Elements:

Structural frame and floor slabs, prefabricated cassettes, core walls and stairs, internal finishes

Timber Species:

Spruce, birch, oak

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