Two photos side by side show a restored fa├žade and one that has not been restored. The restored one is white marble, and the unrestored one is weathered and rusted.
Engineers need to understand the differences between preservation, rehabilitation, restoration, and reconstruction. (Photograph courtesy of istock.com/Gerd Harder)

By Robert L. Reid

Preservation engineers should become familiar with The Secretary of the Interior’s Standards for the Treatment of Historic Properties. These standards, which are considered advisory, not regulatory, apply not only to historic buildings but also to a wide variety of historic resource types — including sites, structures, objects, and districts — that are eligible to be listed in the National Register of Historic Places. The standards address four approaches to historic properties: preservation, rehabilitation, restoration, and reconstruction.

Preservation requires retention of the greatest amount of historic fabric along with the building’s historic form. Rehabilitation acknowledges the need to alter or add to a historic building to meet continuing or new uses while retaining the building’s historic character. Restoration allows for the depiction of a building at a particular time in its history by preserving materials, features, finishes, and spaces from its period of significance and removing those from other periods.

Reconstruction establishes a limited framework for re-creating a vanished or nonsurviving building with new materials, primarily for interpretive purposes.

The National Park Service also operates the Historic Preservation Training Center, based in Frederick, Maryland, with branches at more than a dozen parks across the United States, as well as the National Center for Preservation Technology and Training on the campus of Northwestern State University in Natchitoches, Louisiana.

Open to people from the public or private sector who are interested in historic preservation, these facilities offer workshops and programs on researching historical resources and recording existing conditions, defining deterioration problems and quantifying their potential impact, the conservation of major building materials, stewardship of historical resources after preservation, the use of science and technology to advance the field of historic preservation, and other topics.

The Association for Preservation Technology International holds an annual, international conference — this year’s is in Seattle, Oct. 9-14 — as well as local chapter meetings and other events. APT also maintains the Building Technology Heritage Library and offers a Recognized Professional designation to members who demonstrate knowledge, training, and experience working on historic structures.

Robert L. Reid is the senior editor and features manager of Civil Engineering.

This sidebar first appeared in the July/August 2023 print issue of Civil Engineering as “A Preservation Primer.” To read more in-depth coverage about conservation engineering, see “Hands-on experience is key to historic preservation engineering.”