What is a lengthwise grain separation between or through the growth rings of lumber called?

The term for a lengthwise grain separation between or through the growth rings of lumber is known as "shake." This phenomenon occurs when the wood fibers begin to separate along the growth rings, usually due to drying or the natural growth process. It can affect the structural integrity of the wood and is often more pronounced in certain species of trees or in lumber that has not been properly dried.

Understanding shake is significant for contractors and builders as it helps in assessing the quality of the lumber. Recognizing shake in wood can influence decisions on material selection, as it tends to compromise the strength and utility of the lumber in construction projects. While other terms, such as check, crook, and split, describe different types of wood defects or deformations, they do not refer specifically to the growth-ring-related separations that characterize shake. Knowing how to identify shake in lumber is critical for ensuring the longevity and durability of structures constructed with wood materials.