Delivering Consistent Quality
Sawmill, British Columbia
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, shipping and unloading by the buyer.
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.
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.
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.
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.