New Numbers for Dimensional Lumber

"Twelve years and 70,000 pieces of lumber later, the In-Grade testing program yields new lumber design values"

By Paul Spring

In an ambitious, 12-year testing program known as In-Grade, North American lumber producers have been gauging their strength. Or more accurately the strength of their products. The result will be new, tested design values for southern, western, and Canadian dimensional lumber. These values determine the allowable structural limits of each species and size category, which in turn determine the numbers on span tables used by architects, engineers, designers, and builders. The testing brought together the Canadian Wood Council, the Southern Pine Inspection Bureau, the West Coast Lumber Inspection Bureau, and the Western Wood Products Association (WWPA), along with the help of the U.S. Forest Products Laboratory. All told, the various groups tested to destruction over 70,000 pieces of dimensional