This third scheme for the house makes use of an almost identical plan to that for the second scheme (Adam volumes 42/7-13), but the facades make use of Adam's castle style.

This scheme was executed with some minor alterations. The first-floor balconettes on the central and end bay windows of the north front were not executed, and nor were the carved details above these three windows.

The surviving house has tripartite ground-floor windows in the end bays of the north and south fronts. These are not shown in Adam's drawings. It is not known if these were changes made in execution (they are characteristic of Adam), or whether they were alterations made at a later date. It is worthy of note that King describes a contemporary tea caddy in the form of a model of Caldwell House, and this does not include the tripartite windows, suggesting that their creation was a later intervention.

The pepper-pot bartizans on Caldwell House, along with a pair in the carriage ring at Culzean Castle, are the only survivals of their type on an Adam building.