Timber grading is the process of evaluating and categorizing timber based on its physical characteristics, strength, and suitability for specific applications. [1] [2] This classification ensures that timber meets industry standards and is appropriate for its intended use in construction, furniture making, and other applications. [3]
Timber grading (or wood grading) is primarily conducted through two methods:
Visual grading involves the manual inspection of timber by trained graders who assess characteristics such as knots, grain patterns, and defects. This method is widely used due to its simplicity and cost-effectiveness. [4]
Machine grading utilizes mechanical devices to assess the strength and stiffness of timber. This method provides more consistent and objective results compared to visual grading. [5]
Different regions in the globe have established standards to ensure uniformity in timber grading:
Properly graded timber ensures safety, durability, and performance in various applications, such as:
In Europe, strength grading classifies the structural performance of individual timber boards. In accordance with the standards outlined in standards BS EN 338 and EN 14081, timber is subjected to various assessment methods to determine its mechanical properties. Based on these results, a strength class is assigned, providing an at-a-glance indication of the timber’s load-bearing capability. This classification system helps ensure that the right type of timber is selected for specific structural applications. Timber strength classes are categorized based on the type of wood — hardwoods or softwoods. For hardwoods, the classification begins with the letter ‘D’, representing their origin from deciduous trees. The number following the ‘D’ indicates the strength level, with higher numbers denoting greater strength. Available hardwood strength classes include D24, D30, D40, D50, D60, and D70. Softwoods, which come from coniferous trees, are labeled with a ‘C’. The numbering system follows the same principle as hardwoods: the higher the number, the stronger the timber. Common softwood grades include C14, C16, C18, and C24, or (rarely) higher. [9]