When it comes to structural timber in the UK, C24 grade timber is the standard for strength, stability, and safety. Whether you’re building a shed, a timber frame, or internal structural supports, choosing the right timber grade is crucial.
At Nottage Timber Merchants, we supply only C24 graded timber because it offers significant advantages over C16, the lower-strength alternative commonly found in construction.
What is C24 Timber?
C24 is a strength-graded structural timber that has been either machine-stressed or visually graded to meet British and European standards (BS 4978). It’s kiln-dried to below 20% moisture content for maximum stability and regularised for consistent dimensions.
Key characteristics:
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Higher bending strength than C16
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Reduced likelihood of warping, twisting, or shrinking
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Ideal for longer spans and heavier loads
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Sourced from areas with slower growth, producing a tighter, denser grain
C24 vs C16: A Side-by-Side Comparison
| Feature | C16 Timber | C24 Timber (We Supply) |
|---|---|---|
| Strength Grade | Standard | High |
| Bending Strength | 16 MPa | 24 MPa |
| Maximum Span | Shorter spans only | Longer spans up to 50% heavier loads |
| Use | Light structural elements | Roofs, joists, studs, beams, trusses |
| Moisture Content (Kiln Dried) | 20% | 20% or less |
| Stability | Moderate | High; less twisting & warping |
| Suitability | Limited structural use | All structural applications (residential & commercial) |
Note: C16 is often used in DIY or temporary structures but is not approved for high-load or critical structural use in the UK. C24 ensures peace of mind and compliance with building regulations.
Typical Applications for C24 Timber
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Studwork and wall framing
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Joists and rafters
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Roof trusses and structural beams
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Decking frameworks or load-bearing garden structures
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DIY timber frame projects requiring strength and durability
Span Tables: How C24 Performs
Here’s a quick guide for maximum span of C24 timber at different sizes, assuming domestic loadings:
| Timber Size (mm) | Maximum Span (m) - Joist | Maximum Span (m) - Rafter |
|---|---|---|
| 47 x 100 (4x2) | 3.0 | 2.5 |
| 47 x 150 (6x2) | 4.0 | 3.5 |
| 47 x 200 (8x2) | 5.0 | 4.0 |
| 47 x 225 (9x2) | 5.5 | 4.5 |
Tip: Always check local building regulations before finalising your span requirements. Our team can provide guidance for bespoke projects.
Why You Should Only Use C24
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Safety: C24 reduces the risk of structural failure under heavy loads.
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Durability: Less prone to twisting, shrinking, or warping over time.
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Professional Standard: All UK building codes assume C24 as the minimum for structural timber.
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Ease of Use: Kiln-dried and regularised for consistent sizing, making cutting and joining simpler.
Our C24 Timber Range
At Nottage Timber Merchants, we stock a variety of sizes to suit every project:
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47 x 50 mm (2x2)
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47 x 75 mm (3x2)
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47 x 100 mm (4x2)
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47 x 125 mm (5x2)
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47 x 150 mm (6x2)
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47 x 200 mm (8x2)
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47 x 225 mm (9x2)
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47 x 250 mm (10x2)
All kiln-dried, regularised, and pressure-treated options are available for outdoor or internal structural projects.
Summary
Choosing C24 timber over C16 isn’t just a technical preference—it’s a commitment to quality, durability, and safety. Whether you’re a professional builder or a serious DIYer, using C24 ensures your project stands the test of time.
Tip: When in doubt, always choose the higher strength C24. It’s the professional standard in the UK and the only grade we recommend for structural timber projects.
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