What is CLS timber and what DIY projects is it good for?

Man measuring timber stud work inside house
(Image credit: Getty Images)

What is CLS timber? As you might guess from its name it is a type of timber, but the initials identify what type of timber. CLS stands for Canadian Lumber Standard and is commonly a softwood such as pine, fir, or spruce.

The name refers to a standard and process that the timber goes through to get a specific type of  finish. Unsurprisingly, the name comes from the fact that it was originally manufactured in Canada. But, nowadays you will find that most CLS timber sold in the UK will have come from Europe or Scandinavia.

Due to its strength when finished it is a popular choice to build a stud wall, partition walls or timber framed houses. Here we look at the characteristics, uses and cost of CLS timber.    

What is CLS timber and what are its characteristics? 

For a softwood to become CLS timber it needs to go through a specific process that will give it a certain set of characteristics. The common woods used are pine, fir, and spruce which are kiln-dried to remove moisture. This helps stop the wood from warping and cracking and gives it more strength and durability. The process helps kill off mould and bugs to help prolong the life of the timber.

The timber is planed and shaped to give it an even finish with four smooth surfaces and rounded edges to give you a timber that is easy to handle and ready to use.   

What is CLS timber typically used for? 

CLS timber is commonly used in construction and building projects to create stud work and framing.

It is a popular choice for creating stud walls, partition walls and general studwork as it is easy to work with. It doesn’t need any preparation, apart from being cut to length. This makes it a quick and easy construction option, allowing for openings such as doorways and windows and getting accurate cuts.

The characteristics of CLS timber –  strength and durability – make it a good choice for building timber framed houses. It is often used for carcassing including floor joists, roof joists and loft joists and can be used in flat roof construction. 

What are the benefits and advantages of CLS timber? 

One of the main benefits of CLS timber lies in its strength and superior durability over other timber, which is why it is especially popular in internal construction. The process gives a consistent finish, stops warping and the rounded edges make it easy to transport.

CLS timber is treated so that it is moisture resistant and is conveniently available in a host of different sizes and lengths. Before starting a project make sure to measure for building materials and calculate how much timber you are going to need. This will help reduce timber wastage and keep costs down. 

Just make sure to check how the timber has been stored. If it has been stored outside for a long time it may have gotten damp and warped. If the timber has been stored outside – but still in perfectly good condition – store it inside for a few days to help it acclimatise before using.

Should I use C16 or C24 CLS timber? What’s the difference? 

When looking for CLS timber you may well see C16 or C24 in the title or description. So what does it mean and does it matter which one I use? In general C24 rated timber is of higher quality, has a more uniform finish, is aesthetically more pleasing and is typically more expensive.

However, while C16 timber isn’t as strong as C24 timber it is perfectly suited to internal construction projects such as stud and partition walls where it will be covered by plasterboard or wooden board. It is a popular choice and a more cost effective option.  

How much does CLS timber cost? 

The cost of CLS timber depends on the size, length and rating. Typically C24 is slightly more expensive than C16 rated timber, but C16 rated timber is the common option for internal builds.

Common sizes are 2 x 3 inches (50mm x 75 mm) and 2 x 4 inches (50mm x 100mm). To add a little confusion to the issue the actual size for 2 x 3 inches (50mm x 75 mm) timber which has been finished is 38mm x 63mm and 2 x 4 inches (50mm x 100mm) is 38mm x 88mm. These are often the sizes you will see when looking for CLS timber. Common lengths are 2.4m and 4.8m.   

At the low end of the price range expect to pay around £3 - £4 for a 2.4m length of 38mm x 63mm C16 CLS timber like the Metsä Wood Smooth Planed Round edge Untreated Whitewood spruce CLS timber from B&Q.  Larger 38mm x 88mm timber will cost around £4 - £5 for a 2.4m length. But prices can vary from supplier to supplier, so shop around or contact a local supplier to see what price they can offer. 

Steve Jenkins

Steve is Homebuilding & Renovating's DIY content editor, and has been a writer and editor for two decades. He is an avid DIYer with over 20 years of experience in transforming and renovating homes. He specialises in painting and decorating, but has strong all-round building skills, having previously worked in the industry for 10 years.