What term is used to refer to structural members greater than or equal to 5 inches in nominal thickness?

The term used to refer to structural members that are greater than or equal to 5 inches in nominal thickness is timber. In building construction, sizes of lumber are categorized to define their applications and structural capabilities, with "timber" specifically referring to the larger dimensions used in load-bearing scenarios. This distinction is crucial in fire service and construction because the larger size of timber generally indicates greater strength and stability under load.

Dimensional lumber, on the other hand, typically refers to smaller cross-sectional sizes and is used for various framing purposes. The term "board" usually describes lumber that is less than 2 inches in thickness and is often used for non-structural applications. Framework pertains to the overall structure made up of various components, including both timber and dimensional lumber, but does not specifically denote the thickness of the members. Understanding these definitions helps in assessing building materials and their fire behavior, which is critical in fire service operations.