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Furniture Essentials
Types of Wood
The Basics of Hardwood Lumber Grades
The National Hardwood Lumber Association (NHLA) grades are based on the percentage
of clear-defect free wood on a board. A defect is a irregularity occurring in or on wood that
reduces its strength, durability, or usefulness. Some common defects are:
1.
Knots - embedded limb or branch of the tree. It reduces the strength but might im-
prove the appearance.
2.
Splits/Checks - a seperation of the wood along the grain and across the grain.
3.
Wane - the presence of bark or absence of wood along the edge of the board.
The measurement of this percentage are referred to as clear-cuttings.
The NHLA grades are determined on an imperial measurement system using inches and feet.
A board foot is the unit of measurement. The best grade is the FAS (First and Seconds). This
piece of wood cannot be less than 6 in. wide by 8ft. Long and yield at least 83 1/3 percent clear
B.F: one foot long, one foot wide, one inch thick
To determine the board feet in a board:
Multiply the width in inches by the length in feet and divide by 12. If the lumber is
thicker than one inch, multiply by the thickness.