Underground parking and limited building information have kept ISG and scaffolding contractor GKR on their toes as they tackle a 19-storey refurbishment.
Project: Westminster City Hall refurbishment
Client: Westminster City Council
Contract value: £70m
Main contractor: ISG
Scaffolding subcontractor: GKR Scaffolding
Start date: July 2017
Completion date: November 2018
For half a century, Westminster City Hall has loomed over the central London street connecting the Houses of Parliament to Victoria station.
Serving as the headquarters of Westminster City Council, the building was completed in 1966 and falls some way short of modern efficiency and building performance standards.
These shortcomings are among the driving factors behind a £70m refurbishment being led by main contractor ISG.
One of the main targets of the job is to upgrade the building to a BREEAM Excellent rating, as well as an EPC rating of B. ISG is also installing a double-decker lift system – said to be the first such addition to an existing building in the UK – to reduce waiting times in the lobby by 40 per cent.
Delivering all of this work to a 19-storey building on one of London’s busiest and currently most congested roads – due in part to refurbishment works at nearby Victoria – presented some considerable working-at-height challenges.
Finding an anchor point
Although Westminster City Hall was built in the 60s, ISG and its subcontractors had very little building information to work with.
For scaffolding contractor GKR, this presented a significant problem because the external walls of the building are made up of a series of support and structural columns, with windows in-between.
Scaffolding has to be tied into anchor points as it goes further up a building, which can only be done with a structural column. Without any reliable building information to guide the team, GKR had to manually check the strength of the individual columns to find their anchor points.
“The whole idea is that once we got the cantilevers in and the scaffold is supported, we could take that weight off the ground”
Tony Laws, GKR
“The procedure, once the bolt is in, is that we have a pull tester which will try to pull it out of the column itself,” explains GKR head of health and safety Peter Cullen. “From that, we get a measurement in kilonewtons to see how much it could take.”
GKR contracts manager Tony Laws adds: “Once we established where the structure was, we got a pattern going and we could then drill. The tight patterns [we had to use] are like nothing you’ll see in scaffolding. It took about five or six attempts at design to get that approved.”
Tube and fittings were used for the gantry as well as to create the intricate patterns needed for the anchor points. As the building is an almost perfect square, system scaffolding was used on its exterior.
Working at Height: Special Report
Finding suitable anchor points was just one of the early hurdles GKR encountered on the project.
The area surrounding the city hall is home to an underground car park, the majority of which falls under the west wing of the building. Nearby residential properties meant the west wing also required a series of 10 x 2 m acoustic noise reduction sheeting that had to be erected by five operatives at a time.
This underground car park presented another problem for GKR, as it limited the amount of scaffolding weight the contractor could put on the ground. GKR’s solution was to use a series of cantilevers on levels three, seven, 11 and 15.
Installed every four floors, the cantilevers work by diverting the weight of the scaffold built above the point at which it is installed back into the building. As the scaffolding is wrapped around the whole building, the cantilevers had to be installed up against all four internal walls as well.
“The whole idea is that once we got the cantilevers in and the scaffold is supported, we could take that weight off the ground,” Mr Laws says. “When you build on that, it’s almost like you’re starting again from ground level.”
Westminster City Hall ISG GKR 150145
Mr Cullen adds: “As part of all the engineering, you don’t just look at the structure of the building; you’ve also got to look at the ground to ensure it can take the load. By doing this, the weight is now going down through the beams and its spreading the load out.”
Although the solution has allowed GKR to erect the scaffolding successfully, diverting the load back into the building has meant that both the building and the surrounding area can’t take on any more weight.
“If the client came along and said, ‘I’ve decided I want three more floors on this building’, we couldn’t do it. I’ve never had a job where we’ve had to do this”
Tony Laws, GKR
“Believe it or not, we’re now absolutely maxed out,” Mr Laws says. “This building cannot take any more weight than we’ve got. If the client came along and said, ‘I’ve decided I want three more floors on this building’, we couldn’t do it. I’ve never had a job where we’ve had to do this. It’s the ground around us – if we were doing a normal building twice the size, we wouldn’t have to do this.”
A template for Westminster
Westminster City Council is due to move back into the building in January 2019, and will occupy floors 11-19. Floors 1-10 will be sub-let, bringing in revenues for the council and adding to its efficiency strategy for the building refurbishment.
The council hopes all of the combined elements of the project will produce a template for what good refurbishment looks like, says ISG divisional director Mike Linehan.
“It may be used as a beacon for any other building they want to [refurbish] in the borough of Westminster,” he says. “During this whole project, we’re working alongside the council and trying to help achieve its social value targets. GKR has contributed to that. All the major planning decisions in the borough of Westminster take place in this building; we have to lead by example in terms of installation and approach – it all has to be done correctly.”
Despite the work-at-height and logistical challenges that have emerged, the project is on course to meet its December 2018 completion date and leave the council a fine example of effective planning.