C16 and C24 timber - What is the difference?

The answer to this question is quite simple, this is part of the grading standards in British Standard BS EN 338 and the ‘C’ refers to the material being from ‘coniferous species’ in most cases, this means the timber is likely to be spruce, pine or fir.

C24 graded timber can support a load over a span better than the same size section in C16, so is often specified where there is a higher strength requirement. That said, often it is possible to achieve the same performance in situ using C16 in either a larger section or simply by using more pieces to spread the load.

C16 can be produced in any country as it does not relate to it’s source. C16 in the UK comes from all over Europe, but the majority is produced in the UK and Ireland as this strength class suits the quality and growth-rate of trees from these countries. C24 tends to come from countries or areas where the growing seasons are shorter such as the Nordic and Baltic countries which creates a denser and stronger product, resulting in the timber grading to a higher strength class.

Both products can have either high-pressure or low-pressure (Vac-Vac) treatments and will both perform equally where the appropriate ‘Use-Class’ of treatment is used. To confirm, C16 and C24 are strength classes only and have nothing to do with any durability or preservative performance.