In 1949, shortly after his inauguration, President Harry S. Truman closed the White House to visitors and launched a major renovation and reconstruction of the entire building. Throughout almost all of his ensuing term as President, Truman was forced to reside across Pennsylvania Avenue in Blair House while the White House was completely gutted and rebuilt.
Just why did Truman order such a thorough overhaul of the White House. As the White House museum website explains, the building was on the verge of disintegration:
the main body of the mansion was found to be structurally unsound. Floors no longer merely creaked; they swayed. The president's bathtub was sinking into the floor. A leg of Margaret's piano broke through the floor in what is today the Private Dining Room. Engineers did a thorough examination and found plaster in a corner of the East Room sagging as much as 18 inches. Wooden beams had been weakened by cutting and drilling for plumbing and wiring over 150 years, and the addition of the steel roof and full third floor in 1927 added weight the building could no longer handle. They declared the whole house to be in imminent danger of collapse.
Truman went to Congress and successfuly requested funding to rebuild the White House from the inside out, "leaving only the stout brick outer walls" and a rebuilt interior "largely on the same plan as the existing house—very much the way President James Madison had done in 1814."
Truman selflessly vacated the White House for almost all of his term while the renovation took place. He also pressed for the most modern of construction methods, with concrete and steel beams used in place of the original wooden beams and supports.
Today's White House is a testament to his forward-thinking vision.