C24 Timber

Understanding C24 Timber

C24 timber is a premium grade of structural softwood, surpassing the more common C16 grade in terms of density, strength, and stiffness. The "C" denotes coniferous (softwood), while "24" represents the characteristic bending strength in Newtons per square millimetre. Because it is sourced from slower-growing climates, the wood features tighter grain patterns and fewer physical defects, making it the preferred choice for spans where structural integrity is paramount.

The range includes a variety of depths and widths to accommodate different loading requirements. The 4x2 to 10x2 sections are frequently utilised for floor joists and roof rafters, where the increased depth of the 10-inch timber allows for longer clear spans without the need for intermediate support. For applications requiring additional lateral stability or increased bearing surfaces, the thicker 3-inch profile—ranging from 4x3 to 9x3—provides enhanced performance for wall plates and heavy-duty framing.

All C24 timber in this selection is kiln-dried (KD) to reduce moisture content, which significantly improves dimensional stability and reduces the likelihood of twisting or bowing after installation. To ensure compliance with UK building standards, each piece is typically marked with a grading stamp, providing traceability and assurance of its mechanical properties for structural calculations.

Material Range

• 2-Inch Structural Joists: High-performance C24 graded sections available in depths ranging from 4x2 to 10x2, suitable for primary floor and roof structures.
• 3-Inch Heavy-Duty Sections: Thicker structural timber designed for increased load distribution and stability, featuring sizes from 4x3 up to 9x3.
  
  

Performance Benefits

• Superior Strength: C24 grading offers higher load-bearing capacities and better elasticity than standard C16 timber.
• Dimensional Stability: Kiln-drying ensures the timber maintains its shape and reduces shrinkage once installed within a building envelope.
• Consistency: Slower-grown fibre results in fewer knots and defects, ensuring uniform performance across every length.
• Compliance: Fully graded to meet the structural requirements of UK Building Regulations for domestic and commercial projects.
  
  

Typical Applications

• Floor Joists: Creating robust horizontal platforms for upper floors in residential and commercial builds.
• Roof Rafters: Forming the primary structural skeleton for pitched roof systems, supporting both insulation and tiling loads.
• Timber Frame Construction: Constructing load-bearing internal and external wall panels.
• Mezzanine Floors: Providing the structural framework for elevated storage or office areas in industrial units.
  
  

Specification & Standards

• BS EN 14081-1: Timber structures. Strength graded structural timber with rectangular cross section.
• BS EN 338: Structural timber. Strength classes.
• BS 5268-2: Structural use of timber. Code of practice for permissible stress design, materials and workmanship.
  
  

Related Materials and Construction Uses

C24 timber is designed to function as the core component of a structural carcass. It is frequently used in conjunction with joist hangers, framing anchors, and high-tensile bolts to create secure mechanical connections. To protect the integrity of the timber in external walls or suspended ground floors, it is often installed alongside damp-proof courses (DPC) and breathable membranes to prevent moisture transfer.

In flooring applications, these joists are typically finished with structural-grade chipboard or plywood deckings. When used in roof or floor zones, the voids created by the C24 sections are ideal for the installation of acoustic or thermal insulation, as well as the routing of essential building services.