7th Dec 2022 -

The strongest carcassing timber commonly sold in the UK, C24 timber, offers great levels of both strength and visual consistency, making it perfect for a wide variety of uses within a building project. In this guide from Building Materials Nationwide, we’ll look through the essentials of C24 timber, covering how it’s graded, the woods it’s made from, and its popular uses within a building project. We’ll also show the benefits and detriments of C24 timber compared to C16 timber, the closest alternative.

What is the Meaning of “C24 Timber”?

C24 timber is a graded softwood timber beam that can be used for a wide variety of construction purposes. All C24 timber will be kiln-dried to ensure a low moisture quotient. C24 timber will offer a great level of strength and a uniform appearance, meaning you’ll be able to use exposed boards within a building.

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    Price from: £7.81 £9.37

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How is C24 Timber Graded?

All C24 timber must be stamped and graded, ensuring it has been tested to meet the following standards.

Strength ClassMeasurementPassing Amount
Bending Parallel to GrainN/mm27.5
Tension Parallel to GrainN/mm24.5
Compression Parallel to GrainN/mm27.9
Compression Perpendicular to GrainN/mm21.9
Shear Parallel to GrainN/mm20.71
Mean Modulus of ElasticityN/mm210800
Minimum Modulus of ElasticityN/mm27200
Characteristic Densitykg/m3350
Average Densitykg/m3420

When looking for carcassing timber in the UK you will typically have the choice of either C16 or C24 timber, with C24 being the stronger of the two. It’s vital when using timber for strength to remember that the C24 rating is for the entirety of the beam. This means that if you cut the beam into cross-sections or decrease its thickness you will need to have it re-rated before you can use it in construction.

What is C24 Timber Made From?

C24 will be made from a variety of softwood trees; it is usually imported but in recent years there have been increasing sources from within the UK. The most common woods for C24 will likely be of the spruce or fir variety.

Is All C24 Timber Treated?

Not all C24 timber is treated, and both treated and untreated beams are available. If you are looking to use C24 timber externally then you will need to opt for a treated model. Timber that is treated with preservatives will be able to withstand rainwater and wind without eroding, and will also be able to resist insects that can bore into them. Treated timber will also offer higher durability when used internally, which can offer benefits to an internal structure too. 

Can C24 Timber be Used Outside?

C24 timber is perfectly acceptable to use outside, as long as you opt for a model that has been treated. Treated timber can withstand the elements, making it perfect for decking, external structures, and other uses. When working externally, make sure you order treated C24 timber.

What Sizes of C24 Timber Are Available?

Suppliers will sell C24 Timber in a wide range of sizes. For instance, Building Materials Nationwide sells C24 Timber in the following sizes.

  • 47mm x 100mm
  • 47mm x 125mm
  • 47mm x 150mm
  • 47mm x 175mm
  • 47mm x 200mm
  • 47mm x 225mm
  • 75mm x 150mm
  • 75mm x 225mm

As UK timber must be sold in metric sizings, the traditional American imperial measurements cannot be used. To give an approximate comparison, 47mm x 100mm is a 2x4, 47mm x 125mm is a 2x5 etc., while 75mm x 150mm is a 6x3, and 75mm x 225mm is a 6x9.

What is C24 Timber Used For?

C24 timber can be used for all construction purposes and is especially suited to carcassing due to its unbeatable strength and durability. When building a timber structure C24 beams will offer great load-bearing support. They can also be used for other components such as joists within the walls, floor, and ceiling. The flooring itself, whether internal or external,  is another great use of C24 timber. As long as you are opting for treated timber beams you can use them for external work and features. C24 timber boasts a consistent and attractive look, making it suited for exposed use or visible features.

C24 Timber vs. C16 Timber

C24 and C16 are the most popular options for carcassing timber within the UK. Both are comparable but C24 is the superior choice. C16 wood tends to grow faster, with the forced growth process leading to an increase in knots. This will make the timber in C16 beams less durable, and also make them visually flawed. C24 is, therefore, the best choice in situations where strength is of the utmost importance, and in cases where the wood will be visible. C24 timber will offer roughly a 50% improvement in strength over C16 but will come with a higher price tag. Within building projects, C16 timber is often more than strong enough to support weight, and if the beams are hidden within the finished building, its visual imperfections may be irrelevant.

Our Range of Quality C24 Timber

Building Materials Nationwide stocks a comprehensive range of building supplies, including an extensive selection of C24 timber. Within our timber and joinery section, you’ll find high-quality structural timber in a range of sizes. We work with people throughout the industry, getting the products they need delivered to them across the UK.

For our customers in the trades, we offer trade accounts. Our trade account holders gain access to their own dedicated account manager, who’ll be able to help organise large or unusual orders. This includes sourcing products not listed on our website through our network of suppliers. Sign up for a trade account through our website today, or tell us what you need through the contact form below.

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