Structural lumber is lumber that is larger that 2X4 inches and is used in framing houses, or else in the more structural aspect of building. Structural lumber is stress graded and used most often for joists, studs, and general framing.
Structural lumber is graded on the face side, and the higher grades will have a less knotty stock. Straight graining in structural lumber is found in the higher grades.
Grade Stamps on Structural Lumber
With structural lumber, checking the grade stamp will tell you the quality specifics of the lumber. There are two moisture grades, “S-Dry,” which means less that 19 percent water weight of the lumber. “S-Grn” stands for more than 19 percent water weight in structural lumber. This would be known as green wood, which can warp or shrink.
Select Structural, or SEL STR, comes in numbers 1, 2 and 3. Select structural lumber is nearly knot free and is more expensive. The more knots that appear on the board, in grading structural lumber, determine the grade, 1 being highest, 3 being lowest.