GILES WOODFORDE visits the site of the new £112.8m Royal Shakespeare Theatre auditorium emerging in Stratford

It looks as if a bomb has hit it, or there has been a very major fire. Look upwards at the façade of the Royal Shakespeare Theatre in Stratford, and you can see straight through the top-floor windows to the open sky above. The day I visited, a black cloud hovered overhead, and the RST looked for all the world like a very gloomy set design for Elsinore Castle in Hamlet.

But it's all quite deliberate. A £112.8m reconstruction scheme is under way, which will see an entirely new auditorium built between the old stage and foyer blocks, together with a new foyer serving both the RST and the Swan Theatre behind (see cutaway picture). A new tower will provide views over the town, while the higgledy-piggledy clutter of extensions on the River Avon side of the theatre have already been swept away.

The road to this point has been long and tortuous. At one time it was proposed that the whole theatre, designed by Elisabeth Scott and opened in 1932, should be replaced. There were howls of protest from conservationists, theatregoers and Stratford residents alike. While the auditorium was loved by few, the art deco foyer, with its fountain and angular Swedish marble staircase, was cherished by many.

"It was the realisation that a new auditorium could be fitted in between the flytower and the foyer area that unlocked the problem," explained project director Peter Wilson.

The RSC was determined to have a thrust stage auditorium, with the audience on three sides, much closer to the actors - a concept that is being tried out at the Courtyard, a temporary theatre built to keep the RSC in business while the rebuilding takes place.

"The Courtyard shows that a thrust stage auditorium does work on this scale," Peter said as he led me round the building site. "It's a tremendous gift to a project team to have a full-scale replica to learn from. The new stage here in the RST will be a little narrower than the stage in the Courtyard, and we've managed to tighten up the shape a bit, so the furthest seat will be about half a metre closer to the stage than it is in the Courtyard. It sounds like a small amount, but it makes the whole room a bit tighter, and more compact. In the old theatre, the furthest seat in the balcony was 27m from the sweet spot in the centre of the proscenium arch. It's a bit difficult to do exact comparisons because of the different stage format, but from the middle of the thrust stage to the furthest seat will be 14-and-a-half metres in the new theatre - about half the distance in other words. It will also be possible to fly huge pieces of scenery up into the new auditorium roof, which you can't in the Courtyard."

Next Sunday, there's a chance to see for yourself. There will be opportunities to visit areas of the site, ask questions, learn more about the construction process, and meet members of the Project team.

"We've chosen this moment because it's before the new steel superstructure goes up, and the site becomes inaccessible," Peter explained. "People will be able to see the shape of the new auditorium as it's beginning to appear - you'll see the shape of the thrust stage, and the basement as it's being excavated."

Ah yes, the basement. Peter and I have now reached the basement excavations, and notwithstanding the heavy shower that has recently fallen, the area looks distinctly damp.

"After the Shakespeare Memorial Theatre was burnt out in 1926 - its shell now houses the Swan Theatre - they decided to build Scott's replacement on the site of a disused canal basin," Peter told me. "So the basin had to be filled in, and foundations dug down into it. We encountered masses of concrete, which was the 1930s' approach to solving the water problem: instead of pumping it away, they dug as big a hole as they could manage, and filled it with concrete. Where we are joining the new basement on to the old orchestra pit, the big technical challenge is waterproofing the join between the old and the new. At the moment, it's causing a lot of concern and debate about how best to do it."

We returned to the original foyer, which won't be open on Sunday, and which will be carefully sealed up and preserved while the new auditorium rises alongside. In due course it will become an art deco bar. Peter paused reverentially at a small hole in the wall, the size of a single brick.

"It was an ashtray. In the smoke running up the wall, you can see the word ashes', which was cut out in 1930s lettering. We are trying really hard to keep some of the old flavour of the building, and not strip it all back to a clean, brand new feeling. We want to retain what the theatre calls its ghosts."

Visits on Site Sunday, July 6, are every half hour from 1pm to 3.30pm (the site will close at 4pm), and spaces should be booked in advance by contacting the box office on 0844 800 1114. The site is accessible to those with mobility problems and wheelchairs.