Of his London town house, Ptolemy Dean wrote (Sir John Soane and London, 2006, p.196) that No. 19 Curzon Street 'is a very rare and important example of a surviving Soane townhouse addition.... The house was of a fairly typical eighteenth century pattern with a bow window to the rear room overlooking southwards to the garden. Soane's scheme ... was to replace this with a new west-facing room, with a water-closet discretely inserted within the house in place of outside privies. The new room was not left as a rectangle but bowed outwards, with a large window to the west. On the original house, brick piers were removed on three storeys to allow for the insertion of a large sash or casement window with thin glazing bars to admit the maximum quantity of light.'
In the Soane Museum's green box files there is additional information including a detailed report by Ptolemy Dean in relation to proposals for demolishing part of the building including Soane's addition in 1998. However, Buildings of England: London 6: Westminster (S.Bradley and N.Pevsner, 2003, p.520) mentions the 'special interest of Soane's rear addition of c. 1807' which confirms that it was not demolished after all.
Sir John Soane's collection includes some 30,000 architectural, design and topographical drawings which is a very important resource for scholars worldwide. His was the first architect’s collection to attempt to preserve the best in design for the architectural profession in the future, and it did so by assembling as exemplars surviving drawings by great Renaissance masters and by the leading architects in Britain in the 17th and 18th centuries and his near contemporaries such as Sir William Chambers, Robert Adam and George Dance the Younger. These drawings sit side by side with 9,000 drawings in Soane’s own hand or those of the pupils in his office, covering his early work as a student, his time in Italy and the drawings produced in the course of his architectural practice from 1780 until the 1830s.
Browse (via the vertical menu to the left) and search results for Drawings include a mixture of Concise catalogue records – drawn from an outline list of the collection – and fuller records where drawings have been catalogued in more detail (an ongoing process).