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
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