C24 Grade 47 x 200mm x 4.8m Treated Timber
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Product Details
C24 graded kiln dried treated carcassing timber, 47 x 200mm in a 4.8m length. The 8 x 2 inch section is a standard size for longer span floor joists and flat roof joists. Regularised for consistent dimensions and pressure treated for protection against rot and insect attack.
As of August 2026, PriceNailer data confirms that the cheapest price for C24 Grade 47 x 200mm x 4.8m Treated Timber is £10.79 from Jewson across 3 suppliers. Prices have increased by 68.6% over the last 2 months.
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Frequently Asked Questions
What span can 47 x 200mm C24 floor joists cover?
At 400mm centres, 47 x 200mm C24 joists can typically span around 4.0–4.5 metres depending on the load and species. At 600mm centres the span reduces slightly, usually to around 3.5–4.0 metres. Always consult current span tables from TRADA or your structural engineer to confirm suitability for your specific project.
What does C24 grading mean for structural timber?
C24 is a strength class defined under BS EN 338, indicating the timber meets specific mechanical performance requirements including bending, tension, and stiffness values. It is a higher grade than the more common C16, meaning it can carry greater loads over longer spans. C24 timber is strength graded either visually or by machine to ensure structural reliability.
Is this 47 x 200mm treated timber suitable for flat roofs?
Yes, 47 x 200mm treated C24 timber is commonly used as flat roof joists, particularly for spans where a shallower 47 x 150mm section would be insufficient. The pressure treatment provides protection against rot and fungal attack, which is especially important in flat roof constructions where moisture risk is higher. Always ensure adequate ventilation is incorporated into the flat roof build-up.
What is the actual finished size of 47 x 200mm regularised timber?
Regularised timber is processed to a consistent finished size, so 47 x 200mm refers to the actual target dimensions after regularisation, not a sawn nominal size. Minor tolerances of 1–2mm are permitted under BS EN 336, but regularising ensures uniform depth across all joists, which is critical for achieving a flat floor or roof deck without packing.
How many 4.8m lengths of 47 x 200mm timber do I need for a floor?
Divide the floor width by your chosen joist spacing (typically 400mm or 600mm centres) and add one extra joist for the end. For example, a 4m wide room at 400mm centres requires approximately 11 joists. Always add 10–15% wastage allowance for trimming, noggins, and doubled-up joists around openings such as stairs.