The main section of this rambling house is a two-story, stuccoed brick building raised on a tall limestone foundation. A broad Ionic portico shelters the entry, but the most prominent features are stepped gable ends with prominent projecting copings. To the north, earlier portions now serving as rear wings are rather arbitrarily joined to the main block.
The last of the Washington family houses in Jefferson County, Beall Air stands apart from the others. Thomas Beall, whose family name is pronounced Bell (thus the name of the house is phonetically Bel Air), constructed the first portion. He left the property to his grandson, Lewis William Washington, who added the main block. Architecturally, Washington's addition seems late for the c. 1820 date traditionally ascribed, but this may be because of later modifications. Washington, the great-great-nephew of the first president, inherited a sword that Frederick the Great had given his famous ancestor, along with a pair of pistols that General Lafayette had presented. When John Brown raided Harpers Ferry in October 1859, he sent a detachment to kidnap Beall Air's owner and take the relics. Washington was held hostage at the engine house at Harpers Ferry, and when the stronghold was breached, he identified Brown to his rescuers. Because of this notoriety, James Taylor made it a point to visit and sketch Beall Air, but he described it as “anything but imposing.”