Fallingwater, built between 1936 and 1937, and one of the most famous houses in the world, had structural problems from the beginning. An engineering investigation in 1937, reported “the actual stresses in the structure do not fall within the limits of those prescribed by accepted engineering practice. From this standpoint, therefore, the structure does not have a satisfactory factor of safety, or what might be termed reserve strength.” In 1963, Fallingwater was donated to the The Western Pennsylvania Conservancy and in 1995 the Conservancy engaged the services of Robert Silman Associates, P.C. Consulting Engineers, of New York, NY. By exhaustive structural computer analyses, and close examination of Wright’s original drawings, RSA concluded that there was an imperative need for significant strengthening repairs to the house. Silman Associates determined that the most practical solution for strengthening the overstressed cantilever members would be a post-tensioning system. In the interim, steel shoring was installed to stabilize the structure. Silman Associates engaged Schupack Suarez Engineers, experts in post-tensioning design and then a division of The Di Salvo Engineering Group, to design a solution. The completed strengthening system could not alter the original appearance of the house as conceived by Wright. The hidden posttensioning system is a success and has fully strengthened the support members and halted the cracking and deflections in the structure.