From concept to practical completion only a year later, the Sky “Believe in Better” building was designed to use a number of different rapid construction techniques.
Off-site construction and minimised use of wet trades, allowed the team to meet the strict deadline to celebrate Sky’s 25th anniversary celebration.
Despite the rapid programme, the building has not suffered. Far from it. It is one of the first all timber commercial buildings in the UK and is a beautiful statement, with exposed structure and large open spaces.
On 1 October 2013, client Sky set the brief to build a temporary venue to provide a venue to house Sky’s schools programme and hi-tech training for staff and apprentices. However, during discussions the requirements turned from providing a temporary to a permanent building, to be delivered by its original deadline of its 25th anniversary only a year later.
Sky believe in better building
After a rapid rethink, the team started working on a concept for a permanent building with large open spaces and flexible working areas. It proposed a timber building, citing its fast construction and lightweight benefits.
“We proposed timber as a fast way of building a permanent building, because you get rid of wet trades, it’s lightweight and it’s generally machine made in the factory and assembled on site very quickly,” says Arup Associate Director Tim Snelson.
Contractor Mace was already on site on an adjacent building so a deal was negotiated to bring the firm on board. With the architects and engineers already in the same office, the Mace team moved across, and the accelerated programme started to gather momentum.
“Making the big strategic moves together at the beginning,” says Snelson. “What’s the MEP strategy? What’s the structural strategy? What’s the façade doing? It all moves along very quickly when you all sit together.”
We proposed timber as a fast way of building a permanent building, because you get rid of wet trades, it’s lightweight and it’s generally machine made in the factory and assembled on site very quickly
Sign off for the revised concept took around a month and the subsequent two months were taken up with design, planning and procurement. Six weeks in, and Mace started to interview the potential timber contractors which Arup had been consulting with. Having started in October, by 6 December, specialist timber contractor B&K Structures was on board. It set the deadlines for fabrication of the timber members to ensure that the slots in the factory were not missed.
The rapid design process did not end there. By Christmas, the timber frame was signed off for fabrication and the piling design was finished for a January 2014 site start. The earthworks, foundations and ground slab were all completed by early March for the start of the timber frame erection.
The building itself is built from cross laminated timber (CLT) walls and slabs, and glulam beams. It is set on a regular 6m by 8m grid, with a 6m cantilever on the western elevation which protrudes over an external path to give the building more of a presence over the road. The beams are all exposed and therefore all of the services, with the exception of some lighting and a fire system, are contained within a raised floor. To allow the cantilevering beams to extend the 6m out, the increased depth of the beams has been hidden within this raised floor zone meaning the soffit beneath remains consistent.
Inside the Sky believe in better building
Parallel, double 280mm by 720mm glulam beams sandwich the columns and support the CLT floor slab above, which spans the 6m between the beams. To improve dynamics and deflection which generally limit or drive the design of timber buildings, the team carried out an in depth dynamic analysis of the frame.
“We pushed the grids, so we had to do a more in depth dynamic analysis to make sure the footfall analysis performance would be adequate.”
Other CLT buildings built in the UK and Europe, often have concrete cores as part of the stability system for the building. But the Believe in Better building is entirely CLT. Snelson says that the big leap was going from cellular buildings like classrooms to doing open plan offices when choosing to go from concrete to timber.
“[In Europe] It’s partly to do with their fire regulations, as anything over three stories they want a concrete core,” he says. “But here, they stipulate a fire period, and building control is more willing to take your proposal on how you’re to meet those requirements.
So as long as you can demonstrate the required fire rating, they don’t say it must be concrete
The team therefore decided to prove that the building could withstand a fire for the required amount of time and avoid building the for more time costly concrete core. As a result, the whole frame including the core has the required rating of 60 minutes. In addition to this, the core is also protected by fire boarding as a double protection measure.
“It’s partly an architectural thing,” says Snelson. “If you’re not going to expose the timber, and you’re going to have a plasterboard finish, then you might as well use the fire board to do that.”
The design of the foundations was also optimised for speed of construction.
“The foundations are piled,” says Snelson. “We tried to go for one pile per column so that we could get away with not having to build pile caps. We then designed localised thickenings in the ground floor slab above the pile locations rather than separate pile caps and ground beams.”
Construction on site was rapid with the CLT slabs being laid at 600m² to 800m² per week. This had the added benefit over concrete by being able to be walked over straight away, further speeding up the process.
“It’s ready to walk on the second it’s dropped in. You just go along and screw it to the beams,” explains Snelson.
To facilitate the rapid construction and to ensure that the programme was met, Mace had a logistics centre on site. Alongside this, lean construction specialists had regular meetings with the trade contractors to discuss how they could maximise their efficiency on site.
Sky believe in better building at night
“They also ran the value engineering workshops where we were effectively trying to value engineer the programme, how long is this going to take to do this and do that, how could you accelerate this to meet that deadline?” says Snelson. “They didn’t just optimise the site activities; they also optimised the workflow of the design activities.”
The entire structure and envelope of the building was topped out in June 2014 and the fit out followed with equal speed and precision. The finished building was handed over the following October on time for the celebration event.
In terms of cost, Snelson says that cost of the shell and core of the building was skewed due to the rapid construction programme, but that it is comparable with other office buildings.
“The overall budget was around £25M, but of that the shell and core is only around £14M so the shell is around the standard cost,” he said.
- The Believe in Better Building was shortlisted for the 2015 British Construction Industry Awards.