C16 or C24 - Which Grade Should You Choose?

Balconies view Terlings Park case study All timber decks, whether domestic or commercial, are designed to carry specific loads; these include both uniformly distributed and point loads. The grading rules for structural timber are set out within BS 4978, but how do you know which grade to use?

At Marley, all of our timber decking is supplied to a minimum of C16 and we also offer a further strength grade to C24. This is done in house by our fully-trained graders.  

The difference between these two options is based on the performance properties of the timber and the right choice will depend on the project in question.

In many cases, C16 is suitable and if the correct spans are used. This is usually the most cost-effective option that will meet the performance requirements. 

C24 is a more demanding grade, and there are a number of advantages of using it: in the same section as a board graded to C16 a wider joist centre can be used, and a smaller deck board section can be used on the same centres.

Most deck boards aren’t graded. Whilst failure is unlikely, key areas such as deflection - which consequently could cause a trip hazard, or even give the deck a ‘bouncy feel’ - should be carefully considered. 

By choosing graded boards, a cost saving can be made on the sub structure. Our expert team can help with technical guidance on spans and loading.