Martin Redston is correct in his letter (NCE 28 March/4 April) to point out that the new building at 20-32 Baker Street should comply with Building Regulations requirement A3.
The approach taken to satisfy the requirement was to consider and detail each brickwork pier/column supporting the 'doughnuts' to be either a protected element or removable one at a time without causing collapse.
At the lower levels, the most heavily loaded piers arch vertically between the floors, while higher up, the floor slabs are designed to span over the removed support to the next floor beam.
The brickwork above the removed element can then arch through the window aprons /spandrels into adjacent piers.
Simon Lindop, project engineer, Whitby Bird & Partners, 60 Newman Street, London W1T 3DA