Preservation generally favors places that have few alterations and a high degree of integrity, especially when talking about historic fabric and materials. For traditional historic buildings, this approach has worked pretty well.

But for Modernist places, many structures were built with mass-produced products and experimental materials that may not be easily replicated and, in some cases, are now failing. As some replacement materials are no longer in production, there are better-performing options available today.

If we replace using entirely new products that resemble the look of the originals, is that preservation? This question calls into question the overall definition of integrity when talking about Modernist places.

Lever House in New York City is a good example. When built in 1951-52, the 24-story tower was distinctive for its blue-green heat-resistant glass and stainless steel curtain wall. By the 1980s and '90s, the glass façade was failing and deteriorated due to harsh weather conditions, with corrosion bowing and breaking spandrel glass panels.

By the time Lever House changed ownership in the late 1990s, an estimated one percent of the original glass remained, leaving a façade characterized by mismatched replacement greenish glass. Ultimately, a thoughtful renovation of Lever House removed individual elements of the façade and all glass and replaced them with new materials that are nearly identical to the original.

Challenge #13: Constantly Getting “Carded” Problem >