Nondestructive Evaluation: Wood

Preservationists look to methods of nondestructive evaluation (NDE) to answer questions about the condition, strength, and construction details of wood in historic buildings in the interest of saving historic fabric and reducing or eliminating damage to significant historic features or materials caused by investigative probes. Many times, a basic wood inspection can answer questions posed when a structure is being considered for renovation or adaptive reuse (see “Practice Points Number 3: Basics of Wood Inspection,” which addresses visual inspection, probing, and moisture diagnostics). However, when information generated through a basic inspection is insufficient to make informed decisions, advanced investigative techniques should be considered. Since answers to questions about condition, strength, and construction are often concealed in a historic structure, NDE methods are a means to assess hidden conditions and obtain vital information for decision makers. Although considerable research on the NDE of wood has been conducted, there are only limited numbers of NDE methods for assessing timber that are available for field use. These include: • moisture-content measurements • remote visual inspection • resistance drilling • infrared thermography • visual grading • stress-wave measurements • digital radioscopy NDE methods are tools to be used in conjunction with other assessment methods and experience to obtain information about wood that can be used to make decisions concerning appropriate treatments. Table 1 provides a summary of the various NDE methods discussed and the information that can be obtained through their use. This Practice Point introduces the most commonly available NDE methods for in-situ assessment of wood members and construction. They should not be used without understanding the capabilities and limitations of each method. Some methods require more training Practice Points NUMBER 10