Thickness standards
February 18, 2013 | 6:00 pm CST

Q: We buy green lumber for our manufacturing operation and dry it ourselves. I have been told, as part of my training as a lumber buyer, that I need to specify my 4/4 hardwood (mainly oak) lumber 1-1/8 inches thick. Can you explain this number to me please? Some suppliers are averaging less than this value, and it seems to run OK in the plant. Using a thinner piece of lumber should certainly help save our forests.

A: The standard for 4/4 lumber according to the National Hardwood Lumber Association is that green or air-dried lumber must be 1.00 inch thick in the areas on the piece that are used for grading. Similar numbers are available for 5/4 and thicker lumber. This is the only thickness standard for hardwoods. (For softwoods, there are specific standards for thickness that relate to the thickness at the time of grading of the lumber.) After drying, the standard thickness is 1-5/16 inches in the grading area.

It is not a standard or requirement to cut 1-1/8 inch thicker than the nominal thickness, but it is traditionally done that way within the hardwood industry. I have spent a lot of time measuring lumber thicknesses in many hardwood sawmills. Today, the average thickness in good mills is closer to 1-1/16 and not 1-1/8 inch. So, do you have to worry?

What a purchaser, like yourself, is usually most concerned about is the thickness of the thinner pieces; they cannot be too thin for your operation. In the past, it would be common when a mill averages 1-1/8 inch in thickness, that 10 to 15 percent of the lumber would be under 1-1/16 inch thickness, and 2 percent or more under 1-1/32 inch thick. Today, with computer controls in the sawmill, lumber thickness variation is greatly reduced. In a good mill, an average of 1-1/16 inch thickness can result in only 1 to 2 percent of the lumber under 1-1/32 inch. In other words, in a good mill, although the average lumber thickness is less, there will be very little lumber much thinner than the average.

In your case, and for most producers, I believe that you are more concerned about the thickness of the thinner pieces of lumber and not the average thickness. You need to convince your boss that when you buy lumber from a modern, computer-controlled mill, your lumber will not be too thin even if the average thickness is down a little bit. For a sawmill, each 1/32-inch reduction in average thickness is over 2 percent more yield. Purchasing thinner, but not too thin, lumber can indeed save wood and potentially keep prices from rising too fast.

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About the author
Gene Wengert

Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 45 years. He is extension specialist emeritus at the University of Wisconsin-Madison.