Contents:

• What Is CLS Timber
• CLS Timber Sizes And Dimensions
• Choosing The Right CLS Timber Size
• Key Takeaways
• FAQ's

CLS timber is widely used for internal building work, particularly where accuracy and consistency matter. Builders rely on CLS wood for stud walls, partitions, framing, and boxing in services because it comes in predictable sizes that make setting out faster and more precise. When measurements line up properly, boards sit straighter, fixings land where they should, and finishes look cleaner.

CLS stands for Canadian Lumber Standard. It refers to a system of standardised timber sizes and strength grades that helps builders plan layouts, spacing, and fixings with confidence. Unlike rough sawn timber, CLS is kiln dried and planed, which gives it smoother faces, eased edges, and consistent dimensions from length to length.

This guide explains CLS timber sizes, the CLS timber meaning, how CLS dimensions compare with other standard timber sizes, and how to choose the right size for different interior projects.

CLS timber is manufactured to behave predictably once it’s fixed in place. Kiln drying reduces internal moisture, which limits movement after installation. Planning creates uniform faces and eased edges, making it easier to mark out, cut, and fix accurately. These details matter in studwork, where small variations quickly add up across a wall or partition.

CLS timber is strength graded, usually to C16 for general internal framing, with C24 used where higher loads or wider spacings are needed. The grade tells you how much weight the timber can safely carry and how it will perform under stress, which helps when setting stud centres or planning door openings.

Where CLS differs from other timber types is consistency. Rough sawn timber can vary in width and thickness, which slows work and complicates alignment. Pressure-treated timber suits damp or external conditions, but the finish is often rougher. CLS timber offers clean, consistent sections that speed up installation and deliver a neater result for interior carpentry.

CLS timber sizes follow a standardised range, which helps builders plan layouts and set stud spacing accurately. Manufacturers machine CLS wood to consistent sections along the length, so measurements stay predictable during installation. CLS dimensions end up slightly smaller than the nominal size because the timber is planed all around. This reduction matters when setting stud centres, lining openings, or ordering boards to match standard timber sizes. Always plan using finished CLS timber sizes rather than the nominal description to avoid tight fits or uneven spacing.

Standard CLS timber sizes

Suppliers stock CLS timber in a small range of commonly used sections suited to stud walls and general framing. These CLS timber sizes are widely available across UK merchants, although exact stock can vary by supplier:

• 38 x 63 mm

• 38 x 89 mm

• 38 x 140 mm

• 50 x 75 mm

• 50 x 100 mm

Trades people rely on these because availability stays consistent, and replacement timber remains easy to source during a job.

Nominal vs finished CLS dimensions

Nominal size describes the timber section before machining. Finished CLS dimensions describe the size you measure on site. CLS wood is planed all round and supplied with eased edges, which reduces the final width and thickness compared with the nominal size. This difference explains why CLS timber sizes measure smaller than expected when checked with a tape measure. When setting out stud centres, fixing plasterboard, or fitting insulation, always work from the finished CLS measures to keep everything aligned with standard timber sizes.

Selecting the right CLS timber size comes down to how the timber will sit, what it needs to carry, and how clean the finish needs to be. CLS timber sizes are supplied in standard lengths, so pieces often need cutting to suit the space. Getting the size right from the start will help you save time, reduce waste, and avoid alignment issues later.

• Stud walls and partitions

Pick CLS dimensions that suit stud centres and board widths. Consistent CLS timber sizes keep walls straight and make fixing easier. This approach works well when building a stud wall.

• Framing and boxing-in

Use CLS wood that gives enough depth for fixings without crowding the space. This balance matters when framing around services or adding pipe covers.

• General interior carpentry

Standard CLS timber sizes help joints line up cleanly across corners and longer runs, especially where accuracy shows.

• Load and spacing

Heavier loads or wider spans call for larger dimensions or higher grades. Check spacing before fixing to avoid flex or movement.

• Cutting to fit

CLS timber often needs trimming for a proper fit. Use suitable tools for cutting timber, such as circular saws, to keep cuts square and accurate.

• CLS timber sizes follow a standardised range used for internal framing and studwork.

• CLS wood is kiln dried and planed all round for smooth faces and consistent sections.

• Finished CLS dimensions measure slightly smaller than nominal sizes.

• CLS timber is strength graded, typically C16 or C24 depending on load requirements.