This is for all of you still learning – like me, and all of you that just need a little reminder.

Lumber is grouped into different categories such as: dimension lumber, boards, and timbers based on the following cross-sectional dimensions.

Boards: 1 to 1.5 inches thick, 2 inches and wider

Dimension Lumber: 2 to 4 inches thick, 2 inches and wider

Timbers: 5 inches and thicker, 5 inches and wider

Board lumber is graded by evaluating the better face of the board. Natural and manufacturing defects are considered, but strength is not a critical factor (unlike the grading of dimension lumber).

The highest classification of board lumber is called select grade. Select grade is further divided into three categories: B & Better, C Select, and D Select. B is the best but all of the select grades are used in demanding finishing applications.

The next classification is called common grade. Common grade boards generally contain more knots than the select grade. Common grade is divided numerically from 1 to 5 with 1 being the best in appearance. No. 3 and No. 4 common grades are most frequently used for such applications as sheathing or sub-flooring.


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