Decades of poor maintenance, the construction of a fourth story attic during the Coolidge administration, and the addition of a second-floor balcony over the south portico for Harry Truman took a great toll on the brick and sandstone structure built around a timber frame.
By 1948, the house was declared to be in imminent danger of collapse, forcing President Truman to commission a reconstruction and move across the street to Blair House from 1949 to 1951. The work, done by the firm of Philadelphia contractor John McShain, required the complete dismantling of the interior spaces, construction of a new load-bearing internal steel frame and the reconstruction of the original rooms within the new structure. Some modifications to the floor plan were made, the largest being the repositioning of the grand staircase to open into the Entrance Hall, rather than the Cross Hall. Central air conditioning was added, as well as two additional sub-basements providing space for workrooms, storage, and a bomb shelter.
The Trumans moved back into the White House on March 27, 1952. While the house's structure was kept intact by the Truman reconstruction, much of the new interior finishes were generic, and of little historic value. Much of the original plasterwork, some dating back to the 1814–1816 rebuilding, was too damaged to reinstall, as was the original robust Beaux Arts paneling in the East Room. President Truman had the original timber frame sawed into paneling; the walls of the Vermeil Room, Library, China Room, and Map Room on the ground floor of the main residence were paneled in wood from the timbers. (Wikipedia)
(White House Museum, via Retronaut)