When it comes to choosing timber for construction projects, not all wood is created equal. Among the myriad of options available to builders and DIY enthusiasts, C16 and C24 are two classifications of strength graded timber commonly encountered in the UK and Europe. These classifications are particularly important when selecting timber for structural applications, where durability and load-bearing capabilities are paramount.

In this comprehensive guide, we’ll explore what C16 and C24 pressure treated timber are, their differences, applications, and why it’s crucial to know which grade is suitable for your project.

What is Pressure Treated Timber?

Before we dive into the specifics of C16 and C24 timber, it’s essential to understand what pressure treated timber is. Timber is pressure treated by infusing it with preservatives under high pressure. This treatment process makes the wood more resistant to decay, rot, and insect attack, thereby extending its life. This type of timber is particularly ideal for outdoor or structural applications where humidity, damp, and pests could affect the wood’s integrity.

C16 and C24 Timber Grades Explained

The grading of timber, including C16 and C24, refers to the timber’s strength and quality. These grades are determined by various factors such as the wood's density, knots, grain structure, and moisture content. In general, the higher the grade, the stronger and more resilient the timber.

C16 Timber

C16 timber is the most widely used grade for structural timber, recognised for its good strength and performance attributes. It is also the minimum standard for many structural applications. C16 is cost-effective and is suitable for a variety of load-bearing applications where the loads are not overly demanding.

C24 Timber

On the other hand, C24 timber is a higher grade than C16 and, as such, is stronger and has a higher load-bearing capacity. It has fewer defects compared to C16 and is generally sourced from slower-growing trees, which increases its stability and strength. Given its superior characteristics, C24 timber is preferred for more critical structural applications and where higher loads are expected.

Key Differences Between C16 and C24 Timber

  • Strength and Load Capacity: The most significant difference between C16 and C24 graded timber lies in their strength and load-bearing capabilities. C24 timber can support heavier loads and is less likely to deform under weight, making it suitable for projects requiring high levels of structural integrity.
  • Quality and Appearance: C24 timber typically has fewer knots and defects, resulting in a cleaner appearance. This makes C24 a better choice where aesthetics are as important as strength.
  • Price: Due to its higher quality and strength, C24 timber is more expensive than C16. When budget is a concern, C16 can provide a cost-effective solution for less demanding applications.
  • Applications: While both grades can be used for structural purposes, C16 is commonly employed in floor and roof joists, decking frameworks, and landscaping. C24 is favoured for heavy-duty flooring, roof trusses, and high-load bearing environments.

Choosing Between C16 and C24 Timber

Selecting the correct timber grade for your project is crucial for ensuring safety, durability, and performance. Consider the following factors when choosing between C16 and C24 timber:

  • Structural Requirements: Assess the load requirements of your project. For heavy-duty applications, C24 is the better choice due to its higher strength.
  • Budget: If cost is a significant consideration, C16 offers a more budget-friendly option while still providing adequate strength for many applications.
  • Exposure to Elements: For outdoor projects exposed to harsh weather conditions, opting for pressure treated C24 timber can provide additional durability.
  • Aesthetic Preferences: For projects where appearance is important, the cleaner look of C24 timber may be preferable.


C16 and C24 grades of pressure treated timber are staples in construction and carpentry, each serving distinct needs based on their strength, quality, and cost. Understanding the differences between these timber grades enables builders, architects, and DIY enthusiasts to make informed decisions, ensuring that the chosen timber not only meets but exceeds the structural and aesthetic demands of any project. Whether you opt for the versatility and value of C16 or the superior strength and quality of C24, knowing what each grade offers is the key to a successful build.