In the photograph, the side grain is shown to provide understanding of what constitutes a knot defect when the truss member is cut perpendicular to this face. Each dark line of grain indicates an annual growth ring.
In the sections marked A, the face of a sawn member would not show any knots but may show a figured or disrupted grain on the face. In this area, no defect exists.
In section B, a knot would be visible, however, the knot would be considered a “live knot” or “solid knot.” This area the face of the lumber would be considered defect free.
However, in section C, a visible knot with a dark circle around the knot would exist. These knots are called “dead knots” or “loose knots” and would require a reduction in tooth count in the knot area because the knot may not be capable of transferring load to the adjoining wood fiber.
The way to remember this is:
- In the photo, the center of the tree would be to the right with later growth rings to the left.
- Limbs of the tree growing with the tree are generally tight or live knots. They do not count as a defect in the plated area.
- Limbs of the tree where the tree grows around the limb are loose or dead knots. They do count as defects in the plated area!
Knowing your knots will help you understand potential defects and thereby protect the quality of your final products.