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Standards and Grading

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.

In Canada, grading rules exist to maintain a standard among mills manufacturing similar woods so that you are assured 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.

The National Lumber Grades Authority (NLGA) is responsible for writing, interpreting and maintaining Canadian lumber grading rules and standards.

Canadian dimension lumber, timbers and boards are manufactured according to the Standard Grading Rules for Canadian Lumber published by the National Lumber Grades Authority. This NLGA rules are what is used by graders to assign a grade to lumber, timbers and boards.

Grading of dimension lumber

Dimension lumber ranges in thickness from 38 to 89mm (2 inches to 4 inches) and is used for framing applications such as joists, planks, rafters, studs, and small posts or beams. There are three general levels of surface smoothness to which lumber is manufactured: rough, surfaced, or worked. Rough lumber is lumber that has been sawn, trimmed, and edged. The saw blades used for mass manufacturing are coarse toothed for speed of production and, as a result, rough lumber is usually characterized by striations or saw lines.

Surfaced lumber is lumber which has been surfaced after sawing by passing through a planing machine for the purpose of adding smoothness and uniformity of size on one side (S1S), two sides (S2S), four sides (S4S), or a combination of sides and edges. Worked lumber is surfaced lumber that has been further shaped by a jointer or moulder to be matched (tongue and groove), shiplapped, or patterned into a moulding shape.

Grading timber

The two categories of timber are Beams and Stringers (depth more than 51mm greater than width) and Posts and Timbers (of no more than 51mm greater than width), all with a minimum thickness of 140mm. Both categories of timbers, Beams and Stringers, and Posts and Timbers, contain three stress grades: Select Structural, No.1 and No.2 and two non-stress grades (Standard and Utility).

The stress grades are assigned design values for use as structural members. Non-stress grades have not been assigned design values. No.1 or No.2 are the most common grades specified for structural purposes. No.1 may contain varying amounts of Select Structural, depending on the manufacture. Unlike Canadian dimension lumber, there is a difference between design values for No.1 and No.2 grades for timbers. Select Structural is specified when the highest quality appearance and strength are desired.

The Standard and Utility grades have not been assigned design values. Timber of these grades are permitted for use in specific applications of building codes where high strength is not important, as in the case of deck uses, blocking or short bracing.

Timbers are generally not grade marked, since they are surfaced rough and may be used in exposed locations. Timbers are manufactured in accordance with CAS 0141 Softwood Lumber. If needed, a mill certificate may be obtained to certify the grade.

For more information on grading in Canada, go to www.cwc.ca