From many additions made by its various owners, Flat Rock has developed into a handsome residence that reflects its owners' increasing prosperity. Around 1796, James Hooper built a single-pile two-story weather-boarded frame structure with a side-passage plan. In 1819, the Chambers family added a one-bay one-story addition on the right, and c. 1856 Robert S. Bagley added a second story to the 1819 addition and two one-story wings. At that time, the rough stone foundations were stuccoed and scored to resemble ashlar. The end chimneys of the dwelling are granite to the eaves and brick above. As part of the c. 1856 additions, they were capped with polygonal brick stacks, three stacks on the west end and four on the east. Although not many have survived, a number of these stacks appeared on mid-nineteenth-century Lunenburg houses with otherwise plain designs.