In the United States, standards for grading hardwood are set by the National Hardwood Lumber Assn. The standards are voluminous, replete with exceptions, special rules for certain species, and many details. Here we will only try to illustrate the principles behind the grading, with a few indications of how the home woodworker can use them. For further details, see resources, below.
Unlike softwood, most hardwood is used in applications where appearance is crucial, such as furniture. Hardwood being a natural product, no two boards are alike, and almost all contain defects like knots that would be unacceptable in a piece of fine furniture. In most cases, however, only one side of the board will show. The grading of hardwood reflects that; it is based on the number and size of the “clear face cuttings”–rectangular pieces free of defects on the graded side–that could be cut from the board being graded. The other side of a clear face cutting may contain defects, as long as they don't affect the strength of the cutting. The fewer and bigger the clear face cuttings, the higher the board's grade. Grading a board doesn't involve actually sawing the clear face cuttings from it; they are purely conceptual.
The three top grades are
The remaining grades–2A, 2B, 3A and 3B–rarely reach the retail market; manufacturers make flooring, pallets and similar products from them.
Although the National Hardwood Lumber Assn. defines grades called “Firsts” and “Seconds,” in practice the best boards are almost always sold as a combined grade, FAS (which stands for “firsts and seconds”). From 20 to 40 percent of the boards in a lot graded FAS must be Firsts; the actual percentage required depends on the species. Boards must be at least 6 inches wide and from 8 to 16 feet long; in a lot no more than 30% of the boards can be shorter than 11 feet, and only half of those can be 8 or 9 feet long.
FAS grading is based on the poorest side of the board. The clear face cuttings must be no smaller than 4 inches by 5 feet, or 3 inches by 7 feet. As many as 4 cuttings are allowed, depending on the board's area. For a 4 square foot board to qualify as a Firsts, for example, only 1 cutting can be made, but 3 cuttings are allowed in a board with an area of 15 square feet or more. For larger boards, a choice of two numbers of cuttings is offered, but the larger number must take in a greater percentage of the board's area. For example, if the grading of a particular 12 sq. foot board as Seconds is based on getting 3 clear face cuttings out of it, those cuttings must include 83 ¹⁄₃% of the board; but if 4 cuttings are planned, they must take in 91 ²⁄₃% of the board's total surface.
Unlike the other hardwood grades, Selects are graded on the basis of the best side. Minimum width is 4 inches and lengths run 6 to 16 feet. In a lot, 30% of the boards may be 6 to 11 feet long, but only one-sixth of those may be 6 or 7 feet long. Except for those restrictions, Selects over 4 square feet are graded by the same criteria as Seconds. Since Selects are cheaper than FAS, the home woodworker should seriously consider them for any use in which only one side of the board will be seen.
A No. 1 Common board need only be at least 3 inches wide; the minimum clear face cuttings size drops to 4 inches by 2 feet, or 3 inches by 3 feet. In a lot, 10% of the boards may be 4 to 7 feet long, and half of those may be 4 or 5 feet long. Even in the larger boards, where as many as 5 cuttings are permitted, the clear face cuttings will take in at least 66 ²⁄₃% of the board.
The best way of grasping the puzzle-like nature of grading hardwood is to consider a real example. Here is one from the Wood Handbook, by the Forest Products Laboratory of the U.S. Department of Agriculture (Washington, 1974).
In this case, the grader gets a board 12 feet long and 12 inches wide. One side is clear. The grader turns to the poorer side, pictured below.
One end is cracked, bark shows along both edges, and there are several knots. The standard for No. 1 common boards between 11 and 13 square feet says a maximum of 4 clear pieces may be cut, which, if 3 inches wide, must be at least 3 feet long, and if 4 inches wide at least 2 feet–and the cuttings must take in 66 ²⁄₃% of the area of the board. Can the grader show this is a #1 common?
Yes, she can.
The authoritative Rules for the Measurement and Inspection of Hardwood and Cypress is available from the NHLA (https://www.nhla.com).
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Last revised: 19 January 2019.