The building is composed of four pavilions, one at each corner, about square and three stories tall. These surround a central rotunda. Lower sections or "ranges" were placed outside the pavilions. Pervasive complaints of dampness and the poor health of the building's occupants led to the replacement of the wood floors in the 1890s. Balconies were added in 1896–1902 to increase space after a new Smithsonian Building failed to be authorized by the United States Congress. A tunnel was constructed in 1901 to the Smithsonian Institution Building next door.