quality:corruption, quality:correction
Construction

As reported by Frank Lloyd Wright's apprentices at Taliesin, Kaufmann was in Milwaukee on September 22, nine months after their initial meeting, and called Wright at home early Sunday morning to surprise him with the news that he would be visiting him that day. Wright had told Kaufmann in earlier communications that he had been making progress on the plans but in actuality, he had not done anything. After breakfast, amid a group of very nervous apprentices, Wright calmly drew the plans in the two hours in which it took Kaufmann to drive to Taliesin. Witnesses Edgar Tafel and Robert Mosher, Taliesin apprentices at the time, later stated that when Wright was designing the plans he spoke of how the spaces would be used, directly linking form to function.

Wright designed the home above the waterfall: Kaufmann had expected it to be below the falls to afford a view of the cascades. It has been said that he was initially very upset with this change.

The Kaufmanns planned to entertain large groups so the house needed to be larger than the original plot allowed. They also requested separate bedrooms as well as a bedroom for their adult son and an additional guest room. A cantilevered structure was used to address these requests. The structural design for Fallingwater was undertaken by Wright in association with staff engineers Mendel Glickman and William Wesley Peters, who had been responsible for the columns in Wright's revolutionary design for the Johnson Wax Headquarters.

Preliminary plans were issued to Kaufmann for approval on October 15, 1935, after which Wright made an additional visit to the site to generate a cost estimate for the job. In December 1935, an old rock quarry was reopened to the west of the site to provide the stones needed for the house's walls. Wright visited only periodically during construction, assigning his apprentice Robert Mosher as his permanent on-site representative. The final drawings were issued by Wright in March 1936 with work beginning on the bridge and main house in April.

The construction was plagued by conflicts between Wright, Kaufmann, and the contractor. Uncomfortable with what he saw as Wright's insufficient experience using reinforced concrete, Kaufmann had the architect's daring cantilever design reviewed by a firm of consulting engineers. Upon receiving their report, Wright took offense, immediately requesting that Kaufmann return his drawings and indicating that he was withdrawing from the project. Kaufmann relented to Wright's gambit and the engineer's report was subsequently buried within a stone wall of the house.

For the cantilevered floors, Wright and his team used upside-down T-shaped beams integrated into a monolithic concrete slab which formed both the ceiling of the space below and provided resistance against compression. The contractor, Walter Hall, also an engineer, produced independent computations and argued for increasing the reinforcing steel in the first floor's slab—Wright refused the suggestion. There was speculation over the years that the contractor quietly doubled the amount of reinforcement versus Kaufmann's consulting engineers doubling the amount of steel specified by Wright. During the process of restoration begun in 1995, it was confirmed that additional concrete reinforcement had been added.

In addition, the contractor did not build in a slight upward incline in the formwork for the cantilever to compensate for its settling and deflection. Once the formwork was removed, the cantilever developed a noticeable sag. Upon learning of the unapproved steel addition, Wright recalled Mosher. With Kaufmann's approval, the consulting engineers had a supporting wall installed under the main supporting beam for the west terrace. When Wright discovered it on a site visit, he had Mosher discreetly remove the top course of stones. When Kaufmann later confessed to what had been done, Wright showed him what Mosher had done and pointed out that the cantilever had held up for the past month under test loads without the wall's support.

The main house was completed in 1938 and the guest house was completed the following year.