The central portion of the east range of Osterley was removed in c1763-64, but Adam did not design the famous open double portico, surmounted by a pediment until the following decade. The sculptural arrangement within the tympanum of the pediment was executed in accordance with Adam volume 52/81, with the exception of the central medallion, which contains a blank armorial shield. This all survives in situ.

Adam's two designs for griffons (Adam volumes 18/97-98) have long been associated with Osterley. The griffon is a standard motif within the Adam brothers' arsenal of decorative motifs, and these particular griffon designs may have been intended for numerous other projects. Indeed, one of the griffons is sitting, and the other reclining, suggesting that they are details for different designs. However, if they are for Osterley, it is here suggested that they are not intended as details for the ornamentation of the drawing room commode - as suggested by Tomlin - as they both show the beginning of a tail of rinceaux, which the griffon on the commode does not have. They griffons in the pediment at Osterley, however, do possess tails of rinceaux, and are, therefore, considerably closer in design to these drawings.