In 1972 the Senate Committee on Rules and Administration asked the architect of the Capitol to survey the space occupied by senators and staff and report on their work environment. In the decade and a half since the Dirksen Building had opened, the number of persons working for the Senate had grown from 2,500 to 7,000.
This growth resulted in overcrowded conditions, leading some resourceful staff to fashion offices in toilet rooms and improvise meeting rooms in passageways. It was discovered that the average Senate employee occupied a meager 67 square feet of space, less than half of the minimum government standard of 150 square feet.
Under the direction of the Senate Office Building Commission, the Architect of the Capitol, George White, interviewed 16 prominent architects for the "Dirksen Extension," which was soon renamed the Philip A. Hart Senate Office Building after the much-admired senator from Michigan.
On August 8, 1974, the design for the Hart Building was approved. The first construction contract was awarded on May 20, 1975, with excavation beginning in December. Work proceeded in a total of six phases before the first occupant moved in during November 1982.