The erection of the shells was programmed to take two years during which time Utzon needed to prepare designs for the interiors, in particular for the Major and Minor Halls, as well as for the huge glass walls that would close off the ends of the shells. In fact, due to the complex design and construction of the shells, erection took over three years, so Utzon had a year's grace in which to complete his programme.
Lewis' s role was to concentrate on the engineering design of Stage 3, while his on-site team of Ian McKenzie assisted by Peter Rice, Bob Kelman and John Nutt supervised the construction work on Stage 2. Arups moved into a site office at the bottom of the Tarpeian Steps in front of the Botanic Gardens, which had been vacated by Civil and Civic. Hornibrook set up their site office within the podium.
Before Hornibrook could start building the roof structure, some adjustments were required to the columns supporting the shells. These drove down through the podium to the foundations beneath. When the podium had been built, the columns were designed on the basis of the information available at the time, but when Zunz divided the roof into three separate structures and introduced the ribbed scheme, higher design loads were imposed. This meant that columns and floors that had already been constructed required strengthening and additional piers needed to be placed under existing columns.
It was a major task. Kelman wrote to Zunz in London: 'The magnitude of this work in rebuilding these columns is fantastic and could slow the whole progress of Stage 2 down, unless dealt with pretty drastically now.' It had taken two men with jack picks nearly two weeks to cut away just one yard of the high strength concrete. To speed things up, Hornibrook suggested using explosives and called in a specialist