CLS vs C24 timber: what’s the difference?
It’s a common mix-up on materials lists. CLS and C24 describe different things, so a piece of timber can be both.
What CLS means
CLS stands for Canadian Lumber Standard. It’s planed timber with rounded edges, made to consistent sizes such as 38 × 63 mm and 38 × 89 mm. It’s mainly used for internal stud walls, where a smooth, straight, consistent stud makes boarding easier.
What C24 means
C16 and C24 are strength classes. C24 is stronger than C16, so it’s often specified for structural work such as joists and rafters, where your engineer or building control sets the grade.
Which do I need?
For non-structural internal partitions, CLS is the usual choice. For anything structural, follow the specification from your engineer, architect or building control, which will state the size and strength class.
This is a general guide, not a specification. Your builder, architect, building control or the manufacturer will confirm exactly what your project needs.
Get it priced
Need studwork or structural timber? Send your sizes and quantities for a delivered price.
Common questions
Is CLS timber treated?
Not usually. It’s generally intended for dry, internal use. For external or ground-contact work, use treated timber.
Can CLS be C24?
Yes. CLS is a size and finish, and it can be graded to different strength classes. Check the grade on the order if it matters for your job.