| Rules for grading are established by the U.S. Department of Commerce and maintained by
the American Lumber Standards Committee. These standards are enforced by regional
organizations (e.q. Western Wood Products Association, Northeastern Lumber Manufacturers
Association, Southern Pine Inspection Bureau, West Coast Lumber Inspection Bureau, and
others). Three years of training are required to become a grader, and in Washington each
grader is required to pass the Western Lumber grading rules exam. A grader is very
important to the mill because he is responsible for separating lumber products into
appropriate strength categories. At the mill shown in the picture, seventy- two pieces of
lumber per minute are graded by three graders. |
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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
Dimension lumber is further subdivided into five categories based on size
classifications. These classes are structural joists and planks, studs, decking, light
framing, and structural light framing. After the dimension lumber has been separated, the
grader assigns a grade.
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Structural light framing lumber has nominal dimensions of 2" to 4" thickness
and 2" to 4" width, and typically divided into four separate grades:
select structural, No. 1, No. 2, and No.3. Select Structural is the best grade in terms of
strength characteristics and also the most expensive, No. 1 is the second best, and
so on.
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Light framing lumber has nominal dimensions of 2" to 4" thickness and 2"
to 4" width and is divided into three separate grades: construction, standard, and
utility. Construction is the best in this case.
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Stud lumber has nominal dimensions of 2" to 4" thick and 2" to
6" wide. There is only one grade of stud lumber.
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Decking is divided into two grades: select decking and commercial decking. Select
decking is best in this case.
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Structural joists and planks has nominal dimensions of 2" to 4" thickness and
5" or greater width, and are typically divided into four separate grades: select
structural, No. 1, No. 2, and No.3.
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Timbers are also subdivided into two groups by size classification: Beams and
Stringers and Posts and Timbers. Again, after the lumber has been separated, the grader
assigns a grade.
- Visual grades of posts and timbers (nominal dimensions of 5" and thicker and
width not more than 2" greater than thickness) are dense select structural, Dense No.
1, No. 1, and No. 2. Dense select structural is the best grade in terms of strength
characteristics and also the most expensive, No. 1 is the second best and so on.
- Visual grades of beams and stringers (nominal dimensions of 5" and thicker
and width more than 2" greater than thickness) are dense select structural, Dense No.
1, No. 1, and No. 2. Dense Select Structural is the best grade in terms of strength
characteristics and also the most expensive, No. 1 is the second best and so on.
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.
To view some grading in action please click on the picture below. Windows media player 3.0 is required.
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