For years, the timber trade has held a common belief: C24 is 'better' than C16. But is that the full picture? For many common UK projects, from decking frames and floor joists to partition walls and garden room structures, C16 timber not only meets but often exceeds performance requirements.

The real story is that C16 offers a smarter choice. It's a high-quality, structural-grade timber grown and graded right here in Britain. This means you get stable pricing, reliable quality and service, and a significantly lower carbon footprint, all without compromising on the strength and durability your project needs. It’s time to rethink the C16 vs C24 debate.

What Do Timber Grades Really Mean?

Understanding the timber grading system is the first step to making a smarter choice. In the UK, structural timber is visually, and / or sometimes machine graded to assess its strength, with 'C' standing for Conifer. The number that follows, like 16 or 24, indicates its bending strength in Newtons per square millimetre (N/mm²).

• C16 Timber: Has a bending strength of 16 N/mm².
• C24 Timber: Has a bending strength of 24 N/mm².

Both grades comfortably meet UK building regulations for structural applications. While C24 is technically stronger on paper, the difference is often not a critical factor for most domestic and light commercial projects. The truth is, C16 is more than strong enough for the vast majority of jobs. To be classified as C24, the timber must have fewer knots and imperfections, which is why it's often sourced from slower-growing trees in colder climates. However, the strength of C16 is more than adequate for most intended uses.

 

 

Real-World Performance of C16 Timber

Theoretical strength values are one thing, but performance on site is what truly matters. C16 timber consistently proves its worth across a wide range of common applications.

Is C16 Suitable for Outdoor Use?

Yes, absolutely. When correctly pressure-treated, C16 is an excellent choice for outdoor structures. It's ideal for building robust decking subframes, sheds, garden buildings, and exterior joists. The key is ensuring the timber has been treated to the appropriate Use Class for its intended environment.

Can You Use C16 for Floor Joists?

C16 is commonly used for floor and roof joists in UK house building. While C24 can achieve slightly wider spans or carry heavier loads with the same cross-section, a qualified structural engineer will often specify C16 timber at closer centres or with a slightly larger size to achieve the same performance at a lower cost. For most standard residential floors, C16 is the go-to material.

In many scenarios, choosing C24 where C16 would suffice is a case of over-specifying. Stronger isn't always "better" if the additional strength provides no practical benefit for the specific application. Don't pay for performance you don't need.

 

 

Value That Lasts: Stable Prices & Cost Efficiency

Budgeting is a critical part of any building project, and timber costs can have a significant impact. This is where C16 provides a clear advantage.

Because C24 timber is primarily imported from regions like Scandinavia and the Baltics, its price is subject to currency fluctuations, international shipping costs, and supply chain disruptions. This volatility can make accurate project costing a challenge.

In contrast, C16 is grown, sawn, and graded in the UK. This local supply chain provides far more predictable pricing, helping you keep your project on budget. By choosing C16, you avoid wasting money on over-specified materials and benefit from cost stability. In terms of lifespan, a properly treated piece of C16 timber will last just as long as a treated piece of C24 when used in the same application, making it a sound long-term investment.

British-Grown, Sustainable, and Local

When you choose C16 timber, you're making a choice that benefits more than just your project. Most C16-graded timber in Britain is sourced from fast-growing, sustainably managed forests containing Sitka spruce.

This delivers several key advantages:

• Supports British Industries: You are supporting the UK's forestry sector and the thousands of jobs it provides in rural communities.
• Lower Carbon Footprint: Sourcing timber locally drastically reduces "wood miles." This cuts down on transport emissions compared to importing C24 from overseas, making C16 a more environmentally friendly option.
• Reliable Quality Standards: British-grown timber is treated to rigorous UK standards. Whether it is kiln-dried to reduce moisture content or "tanalised" (pressure-treated) with preservatives, you can trust it to be protected against rot and insect attack.

 

 

Built for the British Climate

The UK's damp and variable weather is a key test for any outdoor building material. With the right treatment, C16 timber is more than up to the challenge.

A common question is, can C16 timber get wet? Yes. Once it has been pressure-treated, it is protected against moisture ingress and fungal decay. For applications like decking joists that will be in contact with the ground or remain consistently wet, we recommend using timber treated to Use Class 4 (UC4). Properly treated and incised C16 timber can have a desired service life of 15 years or more.

The type of treatment is crucial. Look for key indicators like kiln-drying, pressure treatment, and the UC3 or UC4 rating to ensure the timber is fit for purpose. For decking frames, treated C16 is an excellent material that withstands the cycles of rain, frost, and damp that define the British climate. To further extend its life, you can apply a sealant, paint, or stain to the cut ends of the timber during installation.

Choosing Between C16 and C24: A Practical Guide

So, how do you decide?

Choose C16 for:

• Most internal stud walls and partitions.
• Floor and roof joists in standard residential projects.
• Decking subframes and garden structures (when pressure-treated).
• Long term projects where cost-effectiveness and price stability are priorities.

Consider C24 only when:

• A structural engineer has specified it for a high-load application.
• You need to achieve the widest possible spans with the smallest timber cross-section.
• The project demands timber with minimal knots for aesthetic reasons.

When sourcing materials, always ensure you are buying from a reputable supplier. Ask questions to ensure the timber is correctly graded, treated, and fit for your intended purpose. A good merchant will help you avoid buying more timber than you need. At MKM, our in-branch experts are always available to offer practical advice to both trade professionals and DIYers, ensuring you get the right material for the job.

 

 

Strong Enough, Smart Enough, British Enough

C16 timber is the smart choice for the modern builder. It delivers the strength, durability, and performance needed for the vast majority of UK construction projects at a more cost-effective and stable price point.

By choosing British-grown C16, you’re not just making a savvy financial decision; you're also supporting local jobs and reducing your project's environmental impact. Build smart, build efficiently, and build with homegrown timber. Browse our collecion of James Jones C16 timber online today, with free local delivery!