Delivering Consistent Quality
Individual pieces of lumber exhibit a wide range in quality and appearance with
respect to knots, slope of grain, shakes and other natural characteristics. Therefore,
they vary considerably in strength, utility and value.
Canada has grading rules that maintain a standard among mills manufacturing similar woods
to assure customers of uniform quality. Grades standardize the quality of lumber at
different levels and are based on moisture content, size and manufacture at the time of
grading, shipment and unloading by the buyer. Mills in British Columbia have each piece
of lumber graded and grade stamped by independent, accredited lumber graders.
The National Lumber Grades Authority (NLGA)
is responsible for writing, interpreting and maintaining Canadian lumber grading rules
and standards. The Canadian Lumber Standards Accreditation Board (CLSAB) monitors the
quality of Canada's lumber grading and identification system.
Canadian dimension lumber, timbers and boards are manufactured according to the Standard
Grading Rules for Canadian Lumber published by the National Lumber Grades Authority. Graders
use these rules to assign a grade to lumber, timbers and boards.
Back to top
Treated Wood Products
Wood can be treated with preservatives that improve service life under severe conditions
without altering its basic characteristics. It can also be pressure-impregnated with
fire-retardant chemicals that improve its performance in a fire.
Back to top
Kiln Drying
The moisture content of freshly sawn timber is higher than it is under normal service
conditions so it is generally dried before being shipped to users. Many British Columbia
wood species can be seasoned easily and uniformly through kiln drying. This increases the
wood's structural performance, reduces swelling and shrinkage, and enhances its appearance
and workability. Virtually all lumber is kiln dried to a moisture content of 19 per cent
or less.
Back to top
Machine Stress Rating
Machine stress-rated and machine-evaluated lumber is readily available for end uses where
high strength is critical, such as truss rafters, laminating stock, I-beams and web joints.
Machine grading measures a characteristic such as stiffness or density that correlates with
the structural properties of interest, such as bending strength. The result is a more precise
understanding of the strength of each piece of lumber than is possible with visually graded
lumber, which allows designers to use full-design strength and avoid overbuilding.
Back to top
Sources
Canadian Wood Council, www.cwc.ca
FPInnovations – Forintek Division, www.fpinnovations.ca