Isaac Royall, Jr. (1719–1781) came into its possession of the property in 1739 following the death of his father. He greatly enlarged it between 1747 and 1750. He more than doubled the depth of the main building, greatly extended the brick end walls correspondingly, and at either end of the house constructed great twin chimneys connected by parapets. Other features he added include the false ashlar siding on the new western facade and great Doric pilasters inserted at the corners. The interior was redone in Georgian wooden paneling, trim, and archways of a quality possibly unsurpassed by any surviving house of the period. Several of the major rooms that survive are original. He expanded a colonial farmhouse into a three story Georgian mansion considered one of the grandest houses of its era in North America. The construction process was largely borrowed from Caribbean construction practices.