For historic buildings and structures, engineers and architects often rely on current standards and design values to determine adequacy of the wood members to remain in service, but current standards are generally based on lower quality material than was used in many historic buildings. Historic structures built before the establishment of building codes or design values for wood products (or structures which lack grade stamps on individual wood members) present a quandary when determining what design values are appropriate. Frequently an assumed species and grade are assigned, only to show that the wood members are structurally deficient, despite the fact that the structure has stood for decades or centuries without failure. The results of assuming a species and/or grade are often an overly conservative estimate of the design values and unnecessary replacement, repair and retrofit decisions along with associated unnecessary project costs and destruction of historic fabric.
This grading protocol is a review of historical wood testing and standards development, wood condition assessment basics, and a query-based wood grading program. The goal of this protocol is to change the typical decision-making process by giving engineers and architects the means to better understand the grading of wood members in relation to building code requirements.
This report made possible through Grant MT-2210-05-NC-05 from the National Center for Preservation Technology and Training (NCPTT).