Lumber is the wood used especially for structural purposes. It is the beams and planks of wood used in wood processing; typically derived from SPR-spruce, pine, fir.
There’s a wide variety of Lumber so it is graded according to appearance and quality, which helps to choose it right as per the particular requirements. Type of wood and defects also play a role.
Lumber defects are caused by issues with stacking, cutting, and drying wood. The defects should be kept minimal to maintain structural integrity.
Few common defects include:
- Bow- A curve on the plank extending on both ends.
- Check- Noticed around the wood ring as a crack, usually affects only the corners of the board.
- Crook and cup- Crook is a warp on the board, along edges and cup is a hollow face of board.
- Knot– It is naturally occurring. A broken off tree branch causes these circular imperfections. Loose knots may leave a hole.
- Shake and split- A grain between wood’s growth rings that separates them, results in a shake. Crack going all the way through board is a split.
- Twist and wane- Twists are multiple bends on a board and wane is an untrimmed edge on a board or a missing wood.
The U.S. Department of Commerce and the American Lumber Standards Committee, decides the grades of the Lumber, which are as follows-
A] Select structural Lumber
This kind of Lumber has the least amount of defects, Knots that are well spaced, tight, and firm are permitted.
B] No.1 and BTR Lumber
It comes with a few defects; knots like Select structural Lumber are permitted.
C] No.2 Lumber
All knots are permitted as long as they aren’t seen as hindrance. It contains a few defects and is most common grade for framing
D] Construction grade Lumber
Firm, tight knots are allowed. Surface defects are found. Used in light framing.
E] No.3 Lumber
Any amount of knots are allowed and defects that don’t go all the way through the wood are permitted
F] Stud and standard grade Lumber
Knots are not restricted and stud is used as a vertical member of a wall. Standard grade is used for light framing
G] Utility grade Lumber
Used only for light framing. There are very low restrictions on defects.
Spec wood SPF low grade and high grade are also decided on the basis of various specifications like thickness, and all the defects mentioned above.