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by Alan Joch

High-tech toolbox

Historic preservation is on the rise both for the intrinsic value of maintaining architectural treasures and for economic reasons. The Historic Preservation Act of 1966 provides investment tax credits of 20 percent for owners of historic commercial and public buildings that are refurbished using guidelines established by the National Park Service. Thirty-seven states now give an additional tax credit of 10 percent, and many are considering extending credits to historic homes, says Roy Eugene Graham, FAIA, director of the graduate program in urban conservation at The Catholic University of America, in Washington, D.C.

In addition to knowing the intricacies of preservation standards, architects need to understand the construction methods and makeup of historic buildings inside and out, often without the benefit of original design drawings. No matter how advanced technology becomes, the first step in assessing a building’s health remains visual inspection. “We use a host of handy gadgets, but the most important one is our eyes,” says Eric Hammarberg, associate and interim director of preservation at LZA Technology, a New York engineering consultant.

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To probe more completely, architects then may use rectified photography to help assess a building’s condition. Rectified photos are manipulated during the printing process for perspective, so that horizontal and vertical edges aren’t marred by parallax distortions (most CAD software does this automatically). “If you’ve done a good job of adjusting for parallax, you can use that image to trace an elevation or a detail,” says David G. Woodcock, FAIA, director of the Historic Resources Imaging Laboratory in the College of Architecture at Texas A&M University, in College Station.

To peer inside historic structures, architects also use thermal imaging systems, which depict temperature variations through color gradations, thus showing where leaks in a facade, window, or other structural element may lead to unseen internal deterioration. “Cooler areas indicate where water [has penetrated],” says Derek Trelstad, senior project director at LZA.

Other tools include X-ray devices that determine the structural components of wall sections without having to drill into them. When surface cracks appear, motion monitors track the almost imperceptible sagging in historic structures over time. The monitors use small wire segments that span cracks and register minute movements as cracks expand and shrink due to temperature fluctuations or settling. Engineers may monitor hundreds of different cracks on a building and track data for a year or more. “The data highlight where we should focus our efforts,” says Hammarberg.