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Structural timber sorted to C18 or C24
Structural timber must comply with a number of standards and be sorted under CE marking, in this case the most common strength classes in the Netherlands, C18 and C24. This is mandatory so that the timber can be safely used in construction. Timber can be sorted in two ways: visually and mechanically.
Visual sorting
In visual sorting, the wood is inspected by certified assessors on aspects such as grain pattern, number of knots, width of the annual rings, and cracks. This visual sorting is highly reliable because the sorters are trained to determine which aspects are permissible to what extent, allowing them to assign a C18 or C24 label to the wood. Based on the width of the annual rings, for example, a good estimate of the density can be made, which is inherent to the bending strength and volumetric mass of the wood.
Mechanical sorting
In addition to visual sorting, mechanical sorting is becoming increasingly common nowadays, primarily because technologies are becoming better, cheaper, and more efficient. During mechanical sorting, a brief visual inspection for defects is also performed, after which each part is individually measured mechanically to determine the strength class.
Difference between C18 and C24
The difference between C18 and C24 lies in the technical specifications of the wood. The table below lists the technical data from which the differences can be clearly seen:
Name | C18 | C24 | Unit |
Flexural strength | 18 | 24 | N/mm² |
Volumetric mass | 380 | 420 | kg/m³ |
Tensile strength | 10 | 14.5 | N/mm² |
Compressive strength | 18 | 21 | N/mm² |
Which strength class is required?
The strength class required for timber for a specific application is defined in the standard NEN 6760. This standard describes which strength class is suitable for various structural applications. For more detailed information regarding strength classes and applications:
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Do you have questions or need advice?
Are you unsure about the correct strength class for your project, or would you like advice on the application of structural timber? Please feel free to contact us. We are happy to help you find the right solution.
