In 1814 the british attacked and burned down DC federal buildings; they deliberately avoided torching the Patent Office.
The Blodgett's Hotel also housed the U.S. Patent Office. Although the British had destroyed all public buildings, the Blodgett's Hotel and U.S. Patent Office were spared. It was in this building that Congress met between September and December 1815 (when construction of the Old Brick Capitol was complete).
https://en.wikipedia.org/wiki/Burning_of_Washington