Exploratory drawings 61 as understanding of the project evolves. In fact, however clear and powerful a first idea may appear to be it ought to evolve. The longer one works on a project the more closely one becomes aware of the complexities of the interaction between the brief requirements and the realities of the existing building shell. The early conceptual diagram will inevitably change. In fact, it should be a matter of concern if no changes suggest themselves. They may prove to be unnecessary, but there is inevitably a danger of complacency or, as is more often the case, a stubborn commitment to sustaining a seductive first idea at the expense of practical priorities. Above The ground- and first-floor plans on the left of the page were made as overlays on the plan of an existing building, but the only evidence of this is in the circular representations of columns that determine the practical location for new walls. The sketches on the right speculate about the extrusion of the plan, showing options for the curved wall and heights of walls and balustrades. They are drawn from above to emphasize the relationship between plans and elevations. Left This sketchbook drawing records early speculation about how new elements might interact with the existing building. A scribbled note explains how the stair will be excavated from the existing concrete floor, and the drawing makes clear that the rough-hewn concrete treads will be supported on a delicate structure and that the `excavation' will remain exposed.