When W. Brown Morton penned the Secretary of the Interior’s Standards for Historic Preservation in 1976, he addressed the craft aspects of project planning and execution. He could hardly have envisioned that ground-penetrating radar, infrared thermography, and camera-wielding drones — not wood joinery or pointing brickwork — would become the dominant technologies in historic preservation efforts. Conservationists have new materials that can seal masonry and concrete against water penetration, coatings that will bridge active cracks without themselves cracking, and substances that protect iron materials from corrosion.
Perhaps the most exciting uses of these new technologies are in structural engineering. In Italy, the strengthening of unreinforced masonry heritage buildings to resist earthquakes has become legendary, showcased by the rebuilding effort at the Basilica of St. Francis of Assisi. All over the world, structural engineers have new computer-based analytic techniques at their disposal. Older buildings can be mathematically modeled in three dimensions to determine their strengths and weaknesses, as well as to predict the effectiveness of a repair program.
In the United States, structural engineers often find themselves at odds with the Secretary’s standards, which strongly advocate that all interventions be reversible. This is often impossible, as the actions required to save or stabilize a building are so invasive that they can never be reversed.
At Wingspread in Racine, Wisconsin, Frank Lloyd Wright’s largest house, the walls of the octagonal Great Hall were being pushed out as the hip roof flattened. We designed 13 layers of carbon fiber fabric soaked in epoxy to be applied directly to the wood sheathing. This created a one-half-inch thin shell, much like an upside-down boat. The roof tiles were then reinstalled, and the building was fully stabilized.
At Wright’s Guggenheim Museum, the original sprayed concrete exterior walls were badly cracked. The preservation plan required that the existing exterior finish be left visible. Bands of carbon fiber/epoxy reinforcing had to be applied to the inside surface of the walls, a second-best location structurally. Over the past five years, the thermally driven cracks have not reappeared.
Perhaps the most dramatic use of structural technology was the repair of Fallingwater. After 65 years of continuous deflection, the living-room floor girders were found to be dangerously underreinforced. We called for steel cables to be affixed to each side of each concrete girder in a carefully draped geometry. When these were pulled tight, the stresses in the concrete and the reinforcing steel were significantly reversed.
Mies van der Rohe’s 1950 creation of the ideal welded steel-frame glass box, the Farnsworth House in Illinois, is elevated on eight steel columns because the Fox River, only 100 feet from the front door, floods regularly. As flooding has become more aggressive, its present owner, the National Trust for Historic Preservation, commissioned a study that devised a way to raise the house on hydraulic jacks just prior to an impending flood and then lower it back to its original position post-flood. A number of detractors, including Chicago preservation architect John Vinci, voiced opposition to this well-established hydraulic technology, which uses off-the-shelf components, as inappropriate for this revered landmark. But I join the National Trust in strongly endorsing the hydraulic solution as the most effective in responding to all the preservation issues on the site.
Today’s arsenal of technological skills, diagnostics, and products is redefining the art of preservation craftsmanship. Preservation professionals must embrace these new techniques — they are the future.
