How and where to use guide
6.0Mtr X 75 X 225mm C24 Treated Regularised KD Carcassing Timber
Primary applications
This timber is well-suited to floor joists in domestic and light commercial buildings, where its C24 strength grade provides reliable load-bearing performance. It is commonly used for roof battens, ceiling joists, and rafter support in pitched roof construction. Stud walls for internal partitions and external framing benefit from its stability and planed finish. Decking frames and outdoor structures utilise its preservative treatment to resist weathering and ground contact.
- Floor joists in domestic and light commercial buildings
- Roof battens and ceiling joists
- Stud walls for internal partitions and external framing
- Decking frames and outdoor construction
- General structural timberwork and bracing
Indoor applications
For internal use, the timber's regularised planed finish provides a clean appearance and simplifies installation. Floor joists should be sized and spaced according to building regulations and structural design; the 75 × 225mm section is suitable for typical domestic floor spans. Stud walls for partitions benefit from the timber's stability and ease of working. The preservative treatment, whilst primarily for durability, does not prevent internal use and provides additional protection against any moisture ingress.
- Floor joists with appropriate spacing and support
- Internal partition stud walls
- Ceiling joists and roof support
- Planed finish suitable for visible applications
Outdoor and exposed applications
The preservative treatment makes this timber suitable for outdoor structures where it will be exposed to weather and moisture. Decking frames, garden structures, and external bracing can utilise this material. However, even treated timber should be protected from prolonged ground contact; use concrete pads or metal post bases to elevate the timber. Exposed end grain should be sealed with appropriate timber preservative or paint to prevent moisture ingress at cut surfaces. Regular maintenance, including inspection and resealing of cut surfaces, will extend service life.
- Decking frames and garden structures
- External bracing and support timbers
- Elevated from ground contact using pads or bases
- Seal cut surfaces with preservative or paint
- Inspect regularly and maintain protective finishes
Installation and fixing
The regularised planed finish allows for straightforward installation using standard carpentry techniques. Joists should be supported on bearing walls or beams, with adequate bearing length (typically 75–100mm minimum). Stud walls are typically fixed to sole plates and head plates using nails or screws; spacing is usually 400–600mm centres depending on loads and building regulations. Roof battens are nailed or screwed to rafters or trusses. Use corrosion-resistant fixings (stainless steel or galvanised) to avoid staining and deterioration, particularly in outdoor applications. Ensure adequate ventilation beneath floor joists to prevent moisture accumulation.
- Support joists on bearing walls with adequate bearing length
- Fix stud walls to sole and head plates with nails or screws
- Space studs typically 400–600mm centres
- Use corrosion-resistant fixings in outdoor applications
- Ensure ventilation beneath floor joists
- Follow building regulations for spacing and support
Design and structural limits
C24 timber has defined strength properties suitable for structural design to BS EN standards. The 75 × 225mm section provides substantial load-bearing capacity, but actual joist spacing and span depend on the specific load case, deflection limits, and building regulations applicable to your project. For floor joists, typical spans range from 3–5 metres depending on load and spacing; roof applications may allow longer spans. Do not exceed design limits; if your application requires longer spans or heavier loads, consult structural design guidance or a qualified engineer to confirm suitability or specify a larger section.
- C24 grade meets BS EN structural standards
- Typical floor joist spans 3–5 metres depending on load and spacing
- Roof applications may allow longer spans
- Consult structural design for non-standard applications
- Do not exceed design limits without engineer confirmation