The Capitol Extension
The original Capitol was designed when there were just 15 states. By 1850 the number had grown to 31. During the same period House membership increased from 106 to 237. Within a half-century, Congress had outgrown the Capitol.
To meet the needs of a growing nation, wings were added to the north and south ends of the Capitol. The project took 17 years, from 1851-1868. Each wing was three stories high, 140 feet wide, and 235 feet long, and was built of brick with a facing of Massachusetts marble. The wings contained spacious new chambers for the House of Representatives and the Senate, scores of new offices and committee rooms, and grand lobbies, corridors and staircases.
For the convenience of legislators (who often lived in crowded boarding houses) the wings also provided bathing rooms, barber shops, and restaurants. A central heating and ventilation system was run by steam-powered fans, and every room was lighted by gas.
The Capitol extension was designed by Philadelphia architect Thomas U. Walter.