6×2 Timber: Choosing the Right Grade for Structural Work
The 30-second answer: 6×2 timber (150mm x 50mm nominal size) is the industry standard for domestic floor joists, roof purlins, and ridge boards. For structural integrity over significant spans, C24-graded Sawn Treated timber is the recognised requirement, providing the density and load-bearing capacity necessary to meet UK Building Regulations.
Key Takeaways:
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C24 Grade is Standard: While C16 exists, 6×2 is almost exclusively supplied in C24 to maximise span potential in structural flooring and roofing.
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Treated vs. Planed: Sawn Treated is essential for structural carcasses; Planed All Round (PAR) is reserved for visible joinery where aesthetics matter.
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Span Capacity: At standard 400mm centres, a 6×2 C24 joist can typically clear span up to 3.2 metres.
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Moisture Protection: Always use pressure-treated timber for any structural application where the “envelope” is not yet sealed.
What is 6×2 Timber?
6×2 timber is a heavy-duty softwood component measuring 150mm x 50mm (nominal). In the UK, this size is the “workhorse” of residential floor and roof structures. Because it is used primarily for load-bearing, understanding the difference between C16 and C24 is critical; C24 is a superior structural grade with higher fibre density and fewer knots.
When you order 6×2 timber from Materials Market, it is kilned and regularised to ensure dimensional stability. This is a vital part of timber frame construction, as it prevents the “bounce” or “creak” often associated with lower-grade or unregularised materials.
6×2 Applications: From Floors to Roofs
The move from 4×2 timber to 6×2 represents a significant jump in structural capability.
1. Floor Joists
6×2 is the most common choice for domestic floor joists in smaller rooms or home extensions. It provides a robust platform for floorboards or chipboard. For projects requiring even larger clear spans, builders often look toward 8×2 timber.
2. Ridge Boards & Purlins
In “cut roof” construction, the ridge board (the horizontal timber at the apex) and purlins (horizontal supports for rafters) frequently utilise 6×2. Its depth allows for secure birdsmouth joints and sufficient surface area for timber connectors to be fixed properly.
3. Decking Subframes
Due to its thickness, 6×2 Sawn Treated timber is the industry standard for building raised decking platforms, ensuring the structure can support heavy foot traffic and outdoor furniture without sagging.
Options & Variations: Sawn Treated vs. PAR
Choosing between a rough-sawn treated finish and a smooth planed finish depends entirely on visibility and exposure.
| Feature | 6×2 Sawn Treated (Structural) | 6×2 Planed All Round (PAR) |
| Finish | Rough-sawn, pressure-treated. | Smooth, machined on all four sides. |
| Actual Size | ~47mm x 150mm (Regularised). | ~44mm x 144mm (Finished). |
| Durability | High (UC2/UC3 Treated). | Low (Untreated/Interior only). |
| Primary Use | Joists, Rafters, Purlins. | Internal visible framing, Furniture. |
The “Pro” Insight: Dimensional Finished Sizes
When specifying planed timber, always account for the reduction in size. A 6×2 PAR softwood timber will have a finished size of approximately 44mm x 144mm. If your structural calculations are based on a full 150mm depth, using PAR could lead to a non-compliant structure.
6×2 Span Tables & Structural Requirements
Timber sizing must adhere to BS EN 1995 (Eurocode 5). Below is a general guide for 6×2 C24 spans based on a typical domestic floor load ($0.25kN/m^2$ dead load).
| Spacing (Centres) | C24 Max Span (Clear) |
| 400mm | 3.21m |
| 450mm | 3.09m |
| 600mm | 2.76m |
Decision Framework: * If your clear span is under 3 metres, 6×2 C24 Sawn Treated at 400mm centres is the industry standard.
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If your span exceeds 3.2 metres, you should move up to 8×2 timber or reduce your centres to 300mm.
Practical Execution & The “Pro” Edge
Building a floor or roof with 6×2 requires precision to avoid long-term structural issues.
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Crowning: Always check for the “crown” (the natural slight curve) of the timber. Install the joist with the crown facing upwards. When the load is applied, the timber will straighten rather than sag.
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Bridging/Nogging: For spans over 2.5m, install solid blocking or noggings between the 6×2 joists. This prevents the timbers from twisting and significantly increases the stiffness of the floor.
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Treatment of Cuts: Even though we supply pressure-treated timber, any end-cuts made on-site must be brushed with a preservative to maintain the integrity of the treatment.
When to call a professional: If you are building a timber frame extension, your span requirements must be verified by a structural engineer to ensure they meet local Building Control standards.
Soft Conversion FAQs
Is 6×2 timber strong enough for a loft conversion?
Typically, no. Most loft conversions require larger sections (like 8×2 or 9×3) or steel beams because the existing ceiling joists are usually only 4×2 timber. Always consult a structural engineer for loft work.
What is the difference between regularised and PAR?
Regularised timber (Sawn Treated) is machined to a consistent width for structural uniformity but remains slightly rough. PAR (Planed All Round) is sanded smooth for aesthetic applications.
Why do you only sell C24 for 6×2?
We supply C24 as standard for 6×2 because it offers superior strength and allows for the maximum possible span. This provides our customers with the highest level of safety and versatility for structural carcasses.
Project-First Recommendation
For all structural carcasses, including floor joists and roof purlins, the best starting point is 6×2 C24 Sawn Treated. It provides the legal structural requirement and rot protection needed for UK builds. View available lengths and specifications here.
If your project involves visible internal framing or decorative joinery where a smooth finish is required, 6×2 PAR Softwood is the recognised choice. Check current stock levels here.
For a comprehensive look at all structural grades, visit our All You Need to Know About Timber pillar guide.
