In the 1760s Robert Adam was commissioned to design a central block between two wings which had been built 40 years earlier to designs by his father, William Adam. These three finished drawings showing Robert Adam's scheme for the addition of a central block, and they are datable to the late 1760s as the fabric of the house was completed and ready for interior decoration in 1770.

The scheme was executed largely in accordance with Adam's drawings. The exceptions to this can be seen in Adam's plan (Adam volume 43/46), in which an alternative staircase was built, and the hall was given apsidal ends in execution. Further to this, Adam's elevation of the principal (north) front (Adam volume 43/42) shows that he had intended to remodel his father's pre-existing wings, giving them castle-style ornamental details to match his new central block. Although the central block was executed in accordance with the drawing, the remodelling of the wings was never undertaken.