Lumber grading evaluates wood’s appearance or strength, with grades indicating acceptable purposes or non-defective wood percentage. Hardwoods and softwoods are graded differently, with hardwoods classified by clear surface percentage and softwoods by structural integrity or appearance. Grading standards are set by organizations, and different grades are used for different projects. Softwood size is classified based on mechanical criteria, while appearance-graded softwood is graded as A, B, C, or D.
Lumber grading is a system for evaluating the appearance or strength of a piece of wood. The grade indicates the purpose for which the lumber is considered acceptable or the percentage of non-defective or light wood available from a specific size board. Defects commonly include knots, stains, and splits that compromise the board’s appearance or structural integrity. Hardwoods such as oak and maple are graded differently than softwoods, and individuals who perform lumber grading on hardwoods do not require any official certification. Softwoods, such as pine and spruce, are often used in building construction and must be evaluated by certified graders.
In the United States, hardwood lumber grading standards are set by the National Hardwood Lumber Association while the US Department of Commerce issues the US Softwood Lumber Standards. The grade of the lumber will usually appear on the lumber itself. Softwood is generally more marked than hardwood.
Depending on the amount of defect-free wood required, different types of hardwood lumber are commonly used for different projects. Long pieces of decorative molding require longer pieces of light wood, while shorter pieces are needed for cabinetry and furniture. Likewise, defects in appearance are less important if the wood is to be varnished.
Hardwood is classified by the percentage of clear or defect-free surface that can be obtained from the more defective side of a board. For example, the highest quality hardwood plank must have a minimum length of 8 feet (2.43 m) and a minimum width of 6 inches (15.24 cm), and it must be possible to cut the plank into four pieces of light wood that they range from 3 x 7 inches (7.62 x 17.78 cm) to 4 x 5 inches (10.16 x 12.7 cm). If both sides of the board meet this requirement, it is classified as first and second (FAS).
FAS-1 face (FA1) or select graded lumber is often used in place of FAS lumber. Grade FA1 lumber has one side that meets the FAS criteria, but the side with the lowest percentage of light wood only meets the number 1 common grade. Select the lumber meets the area requirements for the common number 1, but for the remainder satisfies the FAS criteria.
Common hardwood grade numbers 1, 2A, 2B, 3A, and 3B require less total area and a lower percentage of light wood than FAS lumber. The percentage of light wood required decreases as the grade decreases, and starting with the common 2B grade, light wood can include “healthy” defects, including intact stains and knots. Common number 1 is also called construction grade and is the grade most often used to build furniture, while number 2A is considered acceptable for furniture and 2B for paint.
Grading of softwood lumber can be based on structural integrity alone or on a combination of structural integrity and appearance. Graded or sized softwood is primarily used in building construction and is rated only on the basis of mechanical properties, such as flexural strength. Woodworkers and craftsmen most often use unstressed or appearance-graded softwood, both of which are graded based on a combination of strength and appearance. Unlike hardwood grading, softwood grading is based on the least defective or best side of the board.
Unstressed or common graded softwood is graded for strength and appearance, although strength is the primary consideration and appearance carries less weight as the grade decreases. The highest grade is number 1 and has the fewest flaws. Grade 3 and below is only used if appearance is not important.
Softwood that is graded primarily for appearance is called graded lumber and is graded as graded A, B, C, or D as the number of defects in the board increases. Even the D-grade selection, however, should contain only minor flaws. When offered for sale, grades A and B are sometimes combined and marked “B&BTR”, which stands for B and better.
Strength and various other mechanical criteria are used to classify softwood size. Appearance is not taken into consideration. This lumber will only be used for construction and will not be visible when construction is complete.
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