Stratford-upon-Avon oozes history with the Royal Shakespeare Theatre firmly at its heart. So stripping out the inside of the 1930s art deco gem to install a more inclusive auditorium was always going to be a delicate and intricate operation.
The obsolete auditorium is sandwiched between a beautiful art deco foyer and the 1872 Swan Theatre, which are both listed. Its deconstruction, which started this October, has had to be carefully thought through by designer Buro Happold and contractor Mace to ensure no harm comes to either of the listed sections of the building.
The roof to the auditorium is made up of huge 2m deep steel trusses. This truss removal is one of the most difficult aspects of the deconstruction of the Grade II listed building. This activity requires two large mobile cranes – one to support men cutting the trusses from their suspended bearing and the other to lift the trusses from their positions.
If the trusses were to slip, they could land on the balcony below which is attached back to the listed art deco foyer. As Wylie says, "A 10t truss dropped 10m onto that balcony would certainly cause some problems."
"We initially proposed one method," says Wylie. "We were going to cut them and let them drop in controlled conditions. However they were not fixed at the bearing locations – one cut and the truss would have collapsed and would have landed on the balcony below which is attached to the foyer." So the trusses were supported by one crane while both ends were cut and then the trusses were lifted clean away.
"The main movement has been thermal," says Wylie.
Wylie's life was made somewhat easier by the existence of existing drawings, kindly donated by Philip Hurst, who was the grandson of the original engineer LB Hurst.
"There have still been surprises," says Wylie. "The trusses were not what we expected. All the trusses were riveted at a time when bolts were more common."
"When working on a project like this, it's important to understand what you don't know," says Wylie. Any assumptions had to be checked.
The depth and weathering profile of the Mercia Mudstone that the new basement piles would be founded upon had to be checked. A borehole approximately 20m deep was driven within the auditorium while the theatre was changing sets between shows in November last year. The whole process was carried out with continuous shift working over a 48 hour period, which had very little float.
"Any overrun and the RSC would have had to cancel the opening night of the show, which was sold out," says Wylie.
At the heart of this project is the audience experience. The stage will be brought forward and the seating arranged around the stage to create a more inclusive atmosphere.
"With Shakespeare you need to clearly hear and see people's faces. The new theatre will provide a more intimate experience. Before people could be 30m away from the stage. Now the furthest seat is 15m away. Even though there is a reduction in numbers, there will be an increase in quality," says Wylie.
The upper tiers of the theatre are not cantilevered. Instead they are supported on a number of discrete columns, none of which are standard steel sections. "We would determine a shape of column that worked and a position. Then we would feed that through to the theatrical consultants. They could enter this into a 3D model and quickly determine if sight lines were compromised," explains Wylie.
There will be huge 3.5m deep trusses over the top of the stage, spanning onto concrete cores.
As well as being designed for the static loads of the lights and the scenery, they have to be designed for the dynamic loads exerted for example if moving scenery stopped suddenly during a power cut.
"Everything revolves around the stage and how the engineering supports that," says Wylie.
"We need to fly 80t of scenery at 5m/s. The structure needs to be stiff enough so that the lights do not move when the scenery
The building is right on the banks of the river Avon, and as the footprint of the new building is bigger than the original, precautions had to be taken to ensure that it did not increase flood risk downstream.
"There's a high water table. We were under a foot of water in July," says Wylie.
To alleviate the problem, a bowl has been sculpted out of the river bank to provide storage for water during floods. It can also be used as an external amphitheatre during drier times.
The high water table also has implications on the waterproofing for the basement. As part of the works, the basement is to be extended. The existing basement, under the stage, is used to drop scenery into and is 7m deep. As the stage is being brought forward, the basement needs to be brought forward too. This will mean digging down and creating a watertight seal to the existing basement at a depth of 8.5m below ground level.
"From existing drawings we can tell that we have sheet piles, plastered bitumen and concrete to break through and connect into," says Wylie.
"We will then have to use temporary waterproofing to create conditions where we can construct high quality permanent waterproofing."
Cross laminated timber boards, which Wylie says are the timber equivalent of concrete precast planks have been used for new floor plates.
As well as being more sustainable, they also help ensure that the existing structure isn't overloaded as they are a lightweight construction.
"It eliminates vast amounts of concrete", says Wylie.
The £112.8M project should be completed and ready for its opening night in 2010.