Wood preservatives and pressure-treated wood: considerations for historic-preservation projects

Abstract

Wood, an abundant resource throughout most of the world, has been used as a building material for thousands of years. Many historic buildings have been built primarily of wood, and masonry and stone buildings generally have wood elements, both structural and architectural. As a biological material, wood is both remarkably complex and yet quite durable if well constructed and maintained. This Practice Point provides guidance on options for extending the service life of wood used in historic structures. It is assumed that the reader is familiar with basic wood nomenclature and anatomy, so those topics are not addressed here. Preserving historic wood fabric is critical to historicpreservation projects. Biodeterioration due to fungi and insect attack can be minimized through the design of repairs, construction practices, moisture management, maintenance, and, if necessary, the use of wood preservatives. Moisture is a primary factor in the onset of biodeterioration; if exposure to high levels of moisture cannot be prevented through moisture management and maintenance, the application of remedial wood preservatives or the use of pressure-treated wood may be warranted. The U.S. Secretary of the Interior’s Standards for the Treatment of Historic Properties emphasize the importance of retaining the historic character of a property, including distinctive materials, features, and spatial relationships. Existing conditions and the factors that caused the deterioration should be carefully evaluated to determine the appropriate level of intervention needed to extend the service life of the wood elements. There are two general paths to extending the life of wood in historic structures: non-chemical means (through moisture management and maintenance) and chemical means (through the use of wood preservatives). Wood preservatives are generally grouped into two categories: preservatives used for in-situ, remedial treatment of existing elements and preservatives used for the pressure treatment of new wood used for the replacement of deteriorated elements.

Citation

Anthony, Ronald W.; Lebow, Stan T. 2015. Wood preservatives and pressure-treated wood: considerations for historic-preservation projects. APT Bulletin. 46(4): 1-9.