Wood Grades Used for Structural Design

In structural design for wood members, wood grade has a significant part to play. Wood specifications are set forth by the National Design Specifications (NDS), and the capacities are derived from this code to design wood structural members for bending, compression, shear, and bearing. Grades of lumber are not to be confused with kiln dried. Some wood grades consist of No. 1, No. 2, No. 3, Select Structural, No. & Better, etc. The NDS specs out lumber based on its species and grade. Each species can have their own set of grades as well. In addition to the standard wood grades that NDS specified in their codes, lumber can also be Machine Stress Rated (MSR). MSR lumber is laboratory tested to increase the overall capacities of standard wood members. Higher capacities in wood members are commonly used when high environmental loads are required in a specific area such as high snow loads and high wind pressures. Below is a great article from Structural Magazine that further explains the significant of wood grades used for structural design.

https://www.structuremag.org/?p=23897

Wood Grading