Timber grading is a technical process of evaluating and classifying solid timber and other wood products. This is based on the physical characteristics and the mechanical strength of the material. This classification process verifies that wood products or timber elements can meet the industry standards, and they are appropriate for use in construction, furniture making, and other applications.
Timber grading is typically carried out using these two methods:
Visual grading is the eye inspection of the timber by trained graders. These technicians can evaluate the wood knots, grain patterns, and other defects. This method is simple and cost effective.
Machine grading of timber uses mechanical devices to assess the strength and stiffness of the material. This method can yield more objective results in comparison to visual grading.
Several established standards are used to ensure stability and reproducibility in timber grading:
When the timber is graded, its overall durability and mechanical performance can be assured in:
In Europe, according to the standards EN 338 and EN 14081, timber is subjected to various assessment methods. Based on the final results, a strength class is assigned for each structural wood element. This classification system assures all of the structural applications. For hardwoods, classification starts with letter 'D', and available hardwood classes include these: D24, D30, D40, D50, D60, and D70.
For softwoods, which are the major structural species used, classes labelled with letter 'C' are distinguished in the softwood grades: C14, C16, C18, C24, C27, or (rarely) higher. Mostly, the classes C24 and C27 are used.