C16 & C24 Timber

In the UK, regularised timber is most commonly classified into two grades: C16 or C24.

The "C" signifies the wood type, specifically Conifer.

The number (24/16) indicates the bend strength - which is based on factors such as imperfections and knots. While C24 is the stronger grade, C16 remains exceptionally strong and is used in numerous wall and roofing applications.

We offer a variety of structural and graded timber - from small 3x2 sizes to larger 8x2 timber. We also offer CLS Timber that is typically graded to C16. Our C16 and C24 timber is available in a range of lengths from 2.4m - 4.8m, most commonly 2.4m, 3m, 3.6m, 4.2m and 4.8m.

Regularised timber refers to timber that has been processed to achieve consistent dimensions and smooth surfaces. This processing typically involves trimming and planing the wood to standardized sizes and shapes, ensuring uniformity in thickness, width, and length. This often results in the timber being a few mm smaller in width and thickness than their "official" size, but is so minimal that it is likely to have no impact on the large majority of projects.

Timber that is kiln dried is placed in kilns where a consistent heat removes excess moisture from freshly cut boards, reducing weight, enhances strength and straightness, and improves its work-ability. Rather than using an air-drying process that can take several months to a year, kiln drying is a faster and more reliable method.

C24 timber represents the pinnacle of structural grading, offering significantly enhanced performance over standard C16 grades. With characteristic strength values of 24 N/mm² in bending and 7.2 N/mm² in tension parallel to grain, C24 timber provides the robust foundation your project requires.

Our C24 structural timber range includes premium quality products from leading British manufacturers including James Jones & Sons, BSW Timber, and Norbord. These industry leaders maintain rigorous quality standards, ensuring every piece meets the demanding requirements of BS 5268 and Eurocode 5 specifications.

Key benefits that set C24 timber apart:

• Enhanced load-bearing capacity - Up to 40% stronger than C16 equivalents
• Superior dimensional stability - Kiln-dried to precise moisture content
• Graded reliability - Machine stress graded to BS 4978 standards
• Versatile applications - Perfect for joists, rafters, and structural framing

Whether you're constructing floor joists spanning greater distances, creating robust roof structures, or building load-bearing walls, C24 timber provides the engineering properties essential for demanding applications. The superior strength characteristics make it particularly valuable in modern construction where longer spans and reduced section sizes are increasingly common.

For loft conversions, C24 timber offers the strength needed to support additional loads whilst maintaining compliance with building regulations. The enhanced stiffness properties ensure minimal deflection, crucial for preventing cracking in ceilings and maintaining structural integrity over time.

At DIY Building Supplies, we understand that specifying structural timber involves more than simply choosing a grade. Our technical team combines decades of practical experience with detailed knowledge of current regulations to help you select the optimal solution for your specific application.

We provide comprehensive support including span tables, load calculations, and fixing specifications to ensure your project meets both performance requirements and building control approval.