CLS

CLS timber is most commonly used for internal stud walls, partition framing, timber framing, boxing-in, dry lining support and general interior construction. It is planed with rounded edges, making it easier to handle than rough sawn timber. Because CLS is usually kiln dried and strength graded, it is a practical choice for creating straight, reliable internal timber frames.

CLS stands for Canadian Lumber Standard. In the UK, it usually refers to planed softwood timber with rounded corners and consistent finished sizes. It is popular for studwork because it is smooth, easy to handle and available in regular structural sizes. Although the name comes from a grading standard, most customers use “CLS” to describe this style of internal framing timber.

Yes, CLS timber can be structural if it is strength graded, such as C16 or C24. This means it has been assessed for construction use and can be used for suitable load-bearing or framing applications. Always check the grade on the product before ordering. For structural work, building control, floors, roofs or load-bearing walls, follow the project specification or ask a qualified tradesperson.

CLS timber is planed with rounded edges and is mainly used for internal studwork and framing. Regularised timber is also machined to a consistent size, but it is often used for broader construction work such as joists, rafters and general structural timber. CLS usually has a smoother, easier-to-handle finish, making it especially popular for interior partition walls.

Untreated CLS timber is normally intended for dry internal use only. It should not be used outdoors unless it has been properly treated and specified for external conditions. If untreated CLS is exposed to rain or long-term moisture, it can warp, swell or decay. For outdoor jobs, choose treated timber that is suitable for the level of exposure.

The right CLS size depends on the height of the wall, spacing of the studs and whether the wall is load-bearing. Common CLS sizes are often used for internal partition walls, but requirements can vary by project. For simple non-load-bearing stud walls, standard CLS sections are often suitable. For structural walls, always check the drawings, span tables or building guidance before ordering.

Yes, CLS timber can be painted or stained, especially for internal projects where the timber may remain visible. Its planed surface needs less preparation than rough sawn timber, but it should still be clean, dry and lightly sanded before finishing. If you are painting, use a suitable primer first, especially around knots or areas where resin may bleed through.

CLS timber is usually sold by its nominal size, but the finished size is smaller because the timber has been planed and machined after sawing. For example, a piece may start as a larger sawn section and finish smaller once it has been dried, planed and rounded. Always check the finished dimensions if the exact size matters for your project.