Building & Carcassing Timber

How to choose Timberlink treated carcassing timber 

Graded C24 or C16 or Ungraded Rough Sawn

What is the difference between C24 and C16 timber? BS EN 338 classifies structural timbers on their strength and stiffness properties and density values based on bending resistance and load bearing capacity. Softwood structural timber, whether it comes from the UK or is imported from Europe, all starts life as a coniferous tree like spruce or pine. Hence the “C” for “coniferous”. The number is just shorthand for the defined bending strength of that strength class:  C24 for 24 N/mm₂ and C16 for 16 N/mm₂ - the higher numbered grade is the better quality.

Both carcassing grades are kiln dried (KD) whitewood, planed smooth and regularised to consistent size with rounded eased edges for easier handling and then pressure treated by Timberlink in our own high pressure treatment plants against fungal and insect attack. Both grades are used for both indoor and outdoor use, when treated to the appropriate Use Class.

C24 timber complies with EN14081-2 and being graded to a higher standard than C16, is usually specified to meet tighter Building Regulations requirements, especially to handle higher loads and wider spans. C24 is more expensive as it is imported, slower grown with both narrower growth rings and hence a tighter grain which leads to greater density, durability and strength. In general terms C24 timbers will have less strength-reducing features like knots. This allows them to achieve the higher performance required by strength class C24, and in this way they may appear to be visually more appealing than most C16 timbers. Timberlink carries a vast range of C24 Timber sizes/sections in depths of 47, 75 and 100mm (2", 3"and 4"), widths from 75 to 300mm (3" to 12") and lengths from 1.8m (6' approx) up to 7.315 m (24').

C16 timber differs from C24 in that it too complies with EN14081 but being usually home and faster grown has wider growth rings and is not as strong or dense as C24 and is only sold in lengths up to 4.8m (16') so cannot meet the same structural loads and spans as C24. Nonetheless C16 graded timber and C16 CLS are widely used in timber frame house construction and being smooth to handle C16 makes for a great general workhorse timber, being cheaper than C24. Timberlink carries 20 sizes/sections of C16 Timber in 47mm (2") that also appear in our more premium C24 range, so you can choose the right grade for your job.

Ungraded Rough Sawn differs from most C24 and C16 timber in that it is not planed - this has the advantage that it treats better than graded timber. Ungraded too is a great workhorse timber extensively used for fencing, roof battens, or where large sections & long length beams and joists are needed. Timberlink only stocks ungraded redwood for fence and gate posts, as the cell structure of Pine especially, enables greater uptake of chemical preservative than in incised timber, which leads to longer life with Use Class 4 treatment for in ground contact. Ungraded timber boards when treated just to Use Class 3 also have better chemical uptakes too than planed timber.