Historical resources, which may include buildings, sites, objects, districts or structures, are protected as part of the environment under the California Environmental Quality Act (CEQA). Local governments are required to determine whether a resource is in fact a resource and whether a proposed project would cause a "substantial adverse change" to the resource.
Substantial adverse change includes demolition, destruction, relocation, or alteration such that the significance of an historical resource would be impaired. While demolition and destruction are fairly obvious significant impacts, it is more difficult to assess when change, alteration, or relocation crosses the threshold of substantial adverse change. The CEQA Guidelines provide that a project that demolishes or alters those physical characteristics of an historical resource that convey its historical significance (i.e., its character-defining features) can be considered to materially impair the resource's significance.
We can both help clients determine if a building is an historic resource (typically through an HRE) and, if it is, help them determine whether the proposed project will fall under the acceptable guidelines for avoiding substantial adverse change.