Water infiltration long plagued Fallingwater, the Frank Lloyd Wright–designed house set over a waterfall in Mill Run, Pennsylvania. But when the site launched World Heritage Preserved, a three-year preservation initiative named for Fallingwater’s inscription to the UNESCO World Heritage List, closing for construction wasn’t a sound option economically.

“Construction would be disruptive to tours, but we had to balance the house’s needs with the visitor experience, plus the financial well-being of our employees,” says Justin Gunther, director of Fallingwater and vice president of the Western Pennsylvania Conservancy, which owns and operates the 1936-37 house built for businessman Edgar J. Kaufmann and his family.

Fallingwater’s preservation team got creative. They scheduled much of the work during winter months, when the house partially closes to the public. To pull this off, crews surrounded it in scaffolding wrapped with insulation board and plastic sheeting. Electric generators powered heating systems in the enclosure to create warm, dry conditions for contractors and their materials.

Inside, masons, roofers, steel conservators, and other specialists worked side by side. Crews replaced waterproofing systems on the flat roofs and terraces. They repointed stone masonry and injected internal wall cavities with grout to prevent future water infiltration. They repaired and, where needed, reconstructed deteriorated concrete. And they remediated rust on the original steel window and door frames as needed and gave them a fresh coat of paint.