The various grades of lumber are determined by the strength of the wood, appearance of the wood and the number of defects. These grades are determined by the U.S. Department of Commerce and the American Lumber Standards Committee. With that in mind, here is your guide to the various grades of lumber, listed from the highest grade to the lowest.
Select Structural Lumber
This is the highest grade of lumber, used for its strength and durability. You’ll find the least number of defects in this grade of lumber. Knots are permitted in certain sizes, as long as they are sound, firm, tight, and well spaced.
No. 1 & BTR Lumber
With this grade of lumber, few defects are allowed. Just like the Select Structural grade, knots are only permitted if they are tight and well spaced.
No. 2 Lumber
No. 2 lumber is the most common grade for framing. Lumber of this grade contains few defects, but knots are allowed of any quality as long as they are well spaced and do not exceed the size regulations.
Construction Grade Lumber
Construction grade lumber is used for light framing. Knots must be sound, firm, encased, and tight. There are limits on most of the defects, with the exception of some occurring only on the surface.
No. 3 Lumber
No. 3 lumber allows for more defects—as long as they don’t go all the way through the wood. Knots are allowed of any quality, as long as they are well spaced.
Stud Grade Lumber
Lumber of this grade has strength and stiffness values that make it suitable for use as a vertical member of a wall. In other words, a stud. There are varying levels of quality within this grade regarding appearance.
Standard Grade Lumber
Standard grade lumber is used for light framing projects. Knots in this grade of wood are not restricted regarding quality.
Utility Grade Lumber
Utility grade lumber is the lowest grade of lumber. It is used only for light framing projects. There are few restrictions on defects, when compared to the other grades.