The conversion of Yarborough house into a new Infirmary was eventually agreed on in June 1810, which is the earliest date of any designs for the Infirmary, using Yarborough House as a location.

There had been a pressing need for a new Infirmary for years, without the opportunity or land to commission one. The old Wren Infirmary had neither space nor convenience in its favour; the numbers of in-patients had dramatically increased in a short space of time. The old Infirmary was also situated above the Great Hall and the only access was via 90 steps (making it difficult for patients to gain exercise or air). A further defect was that the old Infirmary was close to the hospital kitchens and was at a substantial risk of fire (which only increased difficulties caused by the 90 steps). Both Dr Moseley (the Hospital physician) and the hospital surgeon, Mr Keate, advised Soane on the necessary requirements of the new Infirmary (large enough for 80 berths with hot and cold baths), as can be seen implemented in most of the more in-depth plans (SM 67/5/18 and SM 67/5/9).

Soane’s designs for a new Infirmary took two basic forms. The first (SM 67/5/19, SM 67/5/18, SM 67/5/24, SM volume 77/49, SM volume 77/48, SM volume 77/46, SM volume 77/47, SM volume 77/52, SM volume 77/58, SM volume 77/54, SM volume 77/55, SM volume 77/57, SM 67/5/20, SM 67/5/21, SM volume 77/51, SM volume 77/53, SM 67/5/22, SM 67/5/23, SM volume 77/50, SM 67/5/25 and SM 67/5/26) consist of a detached range running from east to west, short cross wings (corresponding to the block plans, SM volume 78/28 and SM volume 78/11). The second design (the built version), shows again a range running from east to west but with south-projecting wings (SM 67/5/9 onwards). The south-eastern portion of Yarborough house was converted as part of this second design, specifically the drawing room.

According to W.H. Godfrey (Survey of London: volume 2: Chelsea, part 1, 1909, p.4) the main part of old Yarborough house ‘probably dated back to 1690 when the site was first leased from the Crown’. At first it was a house for the Hospital treasurer and was later extended by Robert Walpole (probably under Vanbrugh’s influence).

Construction of the Infirmary started in 1810 and continued until 1816 at a total cost of £25,322.19.11. Once Soane had agreed to use the old building for his Infirmary conversion, Godfrey (op. cit. p.5) notes that ‘wherever feasible Soane incorporated the old brickwork in the walls of the Infirmary. The basement, indeed, was largely unaltered, and in this portion some 17th-century brickwork may still be traced.’ Soane used yellow stock brick to tie in with the old brickwork and thus many of the buildings surrounding the Infirmary that Soane later built also had to be of yellow stock brick. The Royal coat of arms was displayed in Coade stone, above the cornice of the north front of the Infirmary but otherwise the final design had minimal ornament. The construction of the Infirmary on the site of Yarborough House would eventually necessitate the demolition and rebuilding of various surrounding service buildings, as they crowded the Infirmary and adversely affected the quality and circulation of air. Soane’s first Chelsea Hospital building was partially destroyed by a bomb in 1941 and subsequently pulled down without any attempt at restoration.

The SM Archive holds two elevations relating to SM 67/4/4, SM 67/4/3, SM 67/5/4 and SM 67/5/5 and one section similar to SM volume 76/7 (Priv.Corr.IX.J.1-3).