C16 vs C24 – What’s The Difference?

If you’ve ever been involved in a construction project that uses kiln-dried softwood, then the terms C16 and C24 are likely familiar to you. Nevertheless, not everyone is aware of their meaning or the distinction between them – so let us help clarify any confusion regarding the time-old ‘C16 vs. C24’ debate with this comprehensive guide.

Firstly, it’s essential to understand that these terms refer to the grade of strength found in carcassing timber. To determine this rating, the British Standards Institution has outlined BS 5268 guidelines which measure a board’s durability by examining its various characteristics such as the slope of grain, woodworm holes and knots – all of which lessen its strength. The ideal piece is straight-grained with no grain deviations present.

Defined by this system, the letter ‘C’ stands for conifer – the type of tree that this timber is made from – and the number indicates strength grade. The higher it climbs, the better its quality; therefore C24 timber surpasses its predecessor C16 in every way.

Out of 12 strength grades in BS 5638 standards, these two timber grades are among the most widely used which is why they dominate our discussion here.

But what advantages make C24 a superior timber grade to C16? And how do we distinguish between them?

What is Timber Grading?

Timber grading is the process of evaluating and classifying different types of wood based on various measurements, most notably their physical and mechanical properties.

This includes factors such as strength, stiffness, durability, and appearance.

Grading helps to ensure that timber is fit for its intended purpose and can meet the performance requirements of construction projects.

Timber is graded using various standards, such as BS 4978 in the UK and the National Grading Rule in the US, which outline specific criteria and methods for grading different types of wood.

What is Carcassing Timber?

Carcassing timber is a specially treated softwood timber that must pass through a kiln-drying process followed by an evaluation of its strength quality: C16 or C24.

After this, the relevant grading mark will be assigned to the timber for identification purposes.

Carcassing timber is routinely relied upon as structural timber in applications such as floor joists, roof battens, roof joists and studwork.

What is C16 Timber?

C16 graded timber is a type of softwood that is graded for use in construction. The “C” in C16 stands for “conifer,” while the “16” refers to the timber’s strength.

C16 timber has a minimum strength of 16 N/mm², which means it can handle a certain amount of weight or load. This type of timber is commonly used in building projects such as roofing, flooring, and wall framing.

C16 timber is typically made from softwood species such as spruce, pine, and fir. It is known for its good quality and durability, making it a popular choice for construction projects. C16 timber is also known for its affordability, making it a great option for those on a budget.

The most common application for C16 timber is for internal construction projects, including wall, floor and roof joist applications.

What is C24 Timber?

Where strength is key, look no further than C24-graded treated timber. With its reputable strength and robust composition, C24 timber is one of the highest-quality types of timber available on the market.

When pitted against the likes of C16-graded timber, C24 reigns supreme, featuring fewer defects, in both its characteristics and appearance.

C24 timber is a higher grade of softwood than C16 timber. Like C16, the “C” in C24 stands for “conifer,” but the “24” refers to the C24’s minimum strength of 24 N/mm², which means it can handle a heavier load than C16 timber. This type of timber is commonly used in building projects such as floor joists, roof rafters, and wall framing.

C24 timber is typically made from slow-grown softwood species such as spruce and pine, which are known for their tighter grain, strength and durability.

This slower growth rate makes C24 timber a popular choice for larger scale projects that require a higher level of strength and load-bearing capacity.

C24 timber is also known for its straightness, which makes it easier to work with and install.

C16 vs C24 – What Are The Differences?

C16 vs C24 Strength and Load-Bearing Capacity:

The main difference between C16 and C24 timber is their strength and load-bearing capacity. C24 timber has a higher minimum strength than C16 timber, meaning it can handle a heavier load. This makes C24 timber a better choice for projects that require a higher level of strength and durability.

C16 vs C24 Straightness:

C24 timber is typically straighter than C16 timber, which makes it easier to work with and install. This is because C24 timber is typically made from slow-grown softwood species, which have tighter grain and fewer natural defects.

C16 vs C24 Cost:

C16 timber is typically less expensive than C24 timber due to a lower strength and load-bearing capacity than C24 timber. This inferiority of strength limits the applications and projects in which it may be suitable.

Furthermore, C16 grade is a more cost-effective option as it permits a few defects. These can include grain aberrations and wanes that may hinder the strength of the wood, in addition to sap stains and uneven surfaces that have negative aesthetic implications.

Despite that, C16 timber is still highly durable and has the desired qualities of bending, compression and density needed for most construction projects.

Which Timber is the Best Choice for Your Project?

The choice between C16 and C24 timber depends on the specific needs of your project. If your project requires a higher level of strength and load-bearing capacity, then C24 timber is the better choice.

When working on less demanding and challenging applications, especially when money is tight, C16 timber may be the better choice.

It is important to note that both C16 and C24 timber is graded for structural use. Both grades have been rigorously  tested to meet certain standards.

 

Timber Grade by Size

When selecting timber for a project, it’s useful to know the typical grades available for each common size. While availability can vary by supplier, the list below shows the most widely stocked sizes and their standard grading in the UK:

• 2×2 timber (47mm x 47mm finished) – Usually supplied in C16, commonly used for studwork and light framing.

• 3×2 timber (47mm x 75mm finished) – Available in C16 and C24, popular for stud walls and general carcassing.

• 4×2 timber (47mm x 100mm finished) – Stocked in both C16 and C24, frequently used for floor and roof joists.

• 5×2 timber (47mm x 125mm finished) – Supplied in C16 and C24, offering added depth for stronger load-bearing applications.

• 6×2 timber (47mm x 150mm finished) – Commonly found in C24 for superior strength, ideal for large floor joists and rafters.

• 7×2 timber (47mm x 175mm finished) – Typically graded C24, chosen where long spans or heavier loads are required.

• 8×2 timber (47mm x 200mm finished) – Usually C24, relied upon for heavy-duty structural applications.

• 9×2 timber (47mm x 225mm finished) – Almost always C24, designed for maximum strength in large-scale structural projects.

• 10×2 timber (47mm x 250mm finished) – Supplied in C24, reserved for demanding builds that require high load-bearing capacity.

• 4×3 timber (75mm x 100mm finished) – Typically supplied in C24, offering extra thickness for heavy-duty framing.

• 6×3 timber (75mm x 150mm finished) – Generally C24, providing superior strength where both depth and thickness are needed.

• 7×3 timber (75mm x 175mm finished) – Usually C24, suited for structural applications needing extra rigidity.

• 8×3 timber (75mm x 200mm finished) – Almost always C24, providing additional support in demanding builds.

• 9×3 timber (75mm x 225mm finished) – Supplied in C24, favoured for very heavy loads and wide-span joists

Smaller dimensions (like 2×2 or 3×2) are more often used in C16 applications, whereas larger dimensions (6×2 and above) are generally stocked in C24 due to the greater strength required for spanning and supporting heavier loads.

C16 vs C24 Conclusion:

As established, C16 and C24 timber are two of the most widely used timber grades in the industry.

C16 timber is the most commonly used form of timber due to its affordability and versatility. This type of wood can be used in a variety of different applications. When you couple this with it’s low cost it makes for an essential resource for any construction project.

The main difference between the two grades is their strength and load-bearing capacity.

C24 timber is the superior grade of the two. Like its counterpart, C16 timber, it has been kiln-dried to decrease moisture content. The difference is that C24 contains fewer defects in regards to both characteristics and looks. This makes it more robust and durable while providing a better aesthetic appeal.