All Carcassing Timbers, whether domestic or commercial, are designed to carry specific loads; these include both uniformly distributed and point loads. The grade rules for the use of structural timber are set out within BS5268-2:2002.
The most common timber grades for softwood boards are C16 and C24.
Timber graded to C16 are generally recommended for most applications and if the correct spans are used this is usually the most cost effective option that will still meet the performance requirements.
Timber graded to C24 will have fewer knots and the knots in the board will be smaller than in a timber graded to C16. C24 graded Timbers are typically used where higher loads are required or wider spans are required.