Drawing 13 appears to have been made in four phases. The plan was probably initially made as a presentation drawing. In August 1791, it was used as a working drawing, with letters and a key added to the plan to instruct workers on site who are building the west staircase and closets (as in drawings 8 and 9) and the walls surrounding the new drawing room. At this stage, Soane stresses that the building works should be finished quickly 'as the family will be soon at Wimp[o]le'. Further modifications to the drawing were added later in rough brown pen to show another set of building works, this time to the east secondary staircase and skylights. Lastly, feint pencil on the drawing shows new powder closets and dressing rooms added between the bedrooms at the north-west corner.

Soane's preliminary design for the east end of the first floor is shown on an early survey drawing of the house, drawing 4. As in drawing 4, drawing 13 has a new stairwell in the east courtyard. The window shedding light into the principal staircase is blocked by this new building, necessitating the insertion of a large lantern overhead. Another skylight is over the lobby at the top of the staircase, with paired columns framing the lobby's entrance.

With a large proportion of the first floor occupied by the upper part of the new drawing room, problems arise with first floor circulation and layout. Soane's alterations attempt to alleviate these problems, but the first floor is essentially divided in two. In the east, Soane attempts to provide some regularity to the design by including a central lobby with inverted rounded ends and a door at each corner. This lobby occupies the former cross gallery; the ends of the gallery are converted to dressing rooms. The west end of the house proves more difficult to arrange, as the drawing room replaced its central circulation space. A long east-west corridor is built in the south range to provide access to these west bedrooms. The north and south ranges have additional staircases leading to the attic storey.

The first floor was further altered in 1800, see drawing 28.

More designs for the first floor are in the National Trust's collection. See David Adshead's catalogue of drawings for Wimpole, Wimpole: architectural drawings and topographical views, 2007, cat. 124-137, pp. 77-80.