Fallingwater Preservation: Restoring an Icon of American Architecture

When Edgar Kaufmann, Sr., a second-generation Pittsburgh department store magnate, fell in love with Bear Run, he likely couldn’t have imagined his weekend house would rival its beauty or become an icon of American architecture – but Frank Lloyd Wright did.

Fallingwater’s Main House and Guest House were commissioned, designed, and built between 1934 and 1939. Wright’s design features reinforced concrete terraces that extend outward like layered stone, paired with long ribbon windows that blur the boundary between interior and landscape. Most striking is the house’s placement directly over the waterfall. “The family thought they were getting a house that looked at the waterfalls and instead they got a house over top of the falls,” says Justin Gunther, Vice President of the Western Pennsylvania Conservancy (WPC) and Director of Fallingwater. Wright intended the family not just to view nature, but to live immersed within it.

Whether Wright’s vision outweighed his knowledge of the limitations of building materials or the design demanded they perform in ways previously untested, the result was the same – constant moisture intrusion and structural problems (as the necessity of a 2002 post-tensioning project proved). 

To keep the doors open and public tours operational, the WPC that owns and cares for the property recognized the need to address the water problems and update building materials that had reached the end of their life. “The whole project started because we were getting prepared for UNESCO World Heritage inscription. One of the primary commitments you make when you become inscribed is ongoing stewardship,” says Gunther.

To gain an understanding of the need, an in-depth study of the building’s failures commenced. As part of this investigation phase, the team at Architectural Preservation Studio, DPC (APS), led by President Pamela Jerome, recommended supplementing the manual CAD drawings and overlapping photo montages created to document the house in the 1990s. 

In May 2016, over the course of four days while guided tours were ongoing, Douglas Emilio of APS produced 3D scans of the exterior using a Faro Focus laser scanner. He returned to Fallingwater in March 2017 for four additional days to capture the interior, providing in total more than 400 scans of the property. “We sent out the scans to a firm in Paris that converts them to AutoCAD,” says Jerome. (That firm, Art Graphique & Patrimoine, was also responsible for the AutoCAD conversion of Andrew Talon’s mapping of the Cathedral of Notre Dame.) The level of information captured and high-definition models that resulted will aid Fallingwater’s preservation efforts well into the future.

Another important part of the full-scale conditions assessment was a test that revealed how far water was migrating through the walls of the Main House. “A team from Wiss, Janey, Elstner Associates, Inc. proved through water testing on the east side of the main chimney mass, at the top of the roof, that water traveled down to the west side of that chimney mass then moved further under two roofing membranes, across the room, and wound up two stories down inside Edgar Kaufmann, Sr.’s bedroom,” notes Jerome.

Following the exhaustive review of problems, APS and WPC put together a multi-phased project, inviting general contractors to bid on the work. “Ten bidders were invited. Only one submitted and it was for $10 million,” recalls Jerome. (The project budget was initially set at $5.4 million.) The team went back to the drawing board and split the project into seven contracts. “We were the GC for the first year, but then Fallingwater hired a preservation project manager in 2023 to act as Clerk of the Works,” recalls Jerome with relief.

In 2020, the COVID-19 pandemic threatened to sink the project. “We had started fundraising using the [2019] World Heritage inscription as a catalyst. And then the pandemic happened and we had to shift all our fundraising to operational support just to survive,” says Gunther. “It wasn’t really until the end of 2021 and beginning of 2022, when we were able to restart the fundraising for the project. Of course, by that time, materials had escalated in price. We had to rebid everything and reset our fundraising goals.” The three-year, nearly $7.5 million World Heritage Preserved project would be Fallingwater’s most comprehensive conservation effort in 25 years.

“It is not the deluge of water in a storm that hurts any building: it is [the] ooze and drip of dirty water in thawing and freezing, increased by slight showers,” said Wright in a Museum of Modern Art 1938 catalog on the house – the museum’s first solo exhibition dedicated to a single building. His remark foreshadowed issues that would trouble the house in the decades to come. Having worked on its preservation for more than 25 years, Jerome saw firsthand the ongoing moisture problem. “When we finished a major restoration project in 2004, we had cured 59 of 60 leaks. By the time we started to do the drawings for the current one, more than half of them had reappeared. Ninety percent of them were related to the stone walls,” she says. 

Built from locally quarried Pottsville sandstone, the masonry was installed in a staggered manner, echoing the uneven stone ledges that project along Bear Run. Protruding stones provide an opportune place for water and melted snow to collect. “One of the challenges we’ve always had here is the traditional stone masonry,” notes Gunther. “Because of the expansion and contraction of the building through changes of the seasons, you get hairline cracks in the mortar joints. Water was always finding its way in.” Compounding the problem was the absence of through-wall flashing. 

Masonry Solutions International, Inc. (MSI) used fiberoptic borescopes and surface-penetrating radar to determine the extent of moisture infiltration. The team found large voids inside the walls, which they remedied with a custom compatible injected fill (CIF) that was inserted into portholes mostly drilled in from the exterior masonry. This solution would eliminate leaks, improve wall stability (by limiting movement), and expand and contract at the same rate as the stone, as well as add heft, acting as a counterweight to the house’s cantilever structure. Once completed, the stone walls were repointed. With the walls now solid, water no longer had a route to travel.

To perfect this technique, masonry work was first performed on the Guest House before moving on to the Main House. When finished, crews had injected almost 12 tons of CIF (approximately 1,740 gallons) into the hollow walls. The solution was put to the test in April 2024 when the area received record rainfall, proving the masonry improvements were successful.

The PMMA flashing formed a natural drip edge, preventing water from backing up into the interior. Epoxy served as a vapor barrier over top of which polyiso insulation and cover board were laid. The final step was a torch-applied modified bitumen roof membrane and pea gravel in a color that replicates the aesthetics of the original 1930s roof assembly. A mock-up of the roofing system was first installed on the Guest House’s “monitor,” a raised roof with clerestory windows over the building’s bathroom, before being installed throughout the rest of the project. “All the products have to be compatible. The way you figure these things out is you do mock-ups and then you let them sit there for a year,” Jerome says.

On Fallingwater’s terraces, flagstones were numbered and removed before old waterproofing was demolished and replaced with a liquid flashing and cold-applied membrane system. Then the stones were reinstalled by Fallingwater’s maintenance team in the precise location from where they came.

Wright’s design for Fallingwater pushed reinforced concrete to its limits, and the concrete mix itself introduced additional complications. Within its first 20 years, the Kaufmanns were performing concrete repairs. “The problem with the concrete is twofold,” says Jerome. “Wright used rounded river pebbles, causing a lack of bond with the cement paste. We also have ASR (Alkali-Silica Reaction) that causes constant cracking. Therefore, a lot of areas were recast as a result because it’s essentially dead concrete; there’s nothing sound to patch to.”

Even the 1930s installation methods proved problematic. Like the rolled edges of the roofs, the rounded caps of parapets were added after the walls cured, creating a cold joint that resulted in cracking over time. As part of the World Heritage Preserved project, Matteo Ferran Structural Engineers assessed the condition of parapets and determined how much demolition was required. Specialists from Graciano Corp. performed concrete reconstruction wherever necessary, replicating the original finish with a hand-applied parge coat after pouring concrete into plywood molds.

The canopied walkway connecting the Main House to the Guest House also required repair where deterioration had exposed the steel-reinforcing bars. New concrete was applied, along with a RureGold fiber-reinforced cement matrix to bolster the canopy structure.