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What is CLS timber?

If you ever looked at a timber yards stock, either online or in-person, you will have no doubt seen the term CLS or CLS Timber. But what exactly is CLS timber?

What is CLS timber?

Surprisingly CLS actually stands for Canadian Lumber Standard but it is widely used here in the UK. It is graded with respect to its strength and as such is used for timber frame construction and carcassing.

Wood Stamped with c16

Wood Stamped with c16

Why Canadian Lumber Standard

So if you are buying CLS timber does that mean it is all being imported from Canada? Fortunately no, it doesn’t. The standard itself originated in Canada before becoming more and more well known and used worldwide.

Most of the CLS you will find here in the UK will be sourced from Scandinavia or sometimes central and eastern Europe.

What Makes CLS Different

It is the strength grading that really sets it apart. This just gives peace of mind when using the wood, you know it is strong enough to do the job at hand.

It is made from either pine, fir or spruce. The wood will be kiln-dried, treated and planed. The edges are also rounded, which makes it a lot easier to handle.

So all in all the main difference is the grading, and then the fact it is planed on all four sides and rounded.

What does c16 or c24 mean?

So CLS is commonly further labelled as c16 or sometimes c24. What does this extra markup mean?

Well, this is the actual strength rating of the wood. It is rated according to British Standard EN 14081-1:2016. The wood is given different ratings all the way up to d70 with this being hardwoods.

Softwoods, which CLS timber is made from, will usually be marked as C16, some are C24 and this should be stronger wood. This is why C24 is a little more expensive than C16.

Can I use CLS outside?

Yes, there is nothing to stop you from using CLS timber outdoors. However, it needs to be treated or else it will just rot away.

So either use a weatherproof sealer, treatment or paint before leaving the wood outside, exposed to the elements.

Should I Buy CLS Timber

Yes, I would recommend it. Due to the fact the timber is planed and rounded it is quite a nice wood to work with. The chances of getting nasty splinters are reduced when compared to using rough sawn timber.

It is also consistent and there is an element of you know what you are getting every time you buy CLS timber.

The nice straight edges also make it easier to line up and also plasterboard. That’s one reason why it is nearly always used when creating a stud wall.

I would however say don’t spend the extra money on C24 lumber. As a DIYer, there really isn’t any reason to, and to be perfectly honest I am sceptical that it really is any different to C16 anyway!


Ian morris

Tuesday 1st of February 2022

Excellently worded for the diyer like me and solved a few of the questions about cls timber thanks for putting it on the site and I'll have a look at your website