C24 Floor Joists Sizing Reference Guide (UK)
Timber grades, section sizes and questions for professional review. No allowable span values are provided; consult official sources and a qualified designer.
Verify against TRADA Eurocode 5 span tables
Numeric span values for floor joists in the UK must be confirmed against the latest TRADA published Eurocode 5 (BS EN 1995-1-1) span tables, NHBC Standards Chapter 6.4, and a structural engineer's calculations. Building Control approval is required for new structural work — under Part A of the Building Regulations in England & Wales, Section 1 of the Scottish Technical Handbook in Scotland, or Part D in Northern Ireland. This page is a planning starting point, not a substitute for design sign-off.
About C24 Softwood
A grade label alone does not establish suitability. Confirm the actual product, grading evidence and intended use with a qualified designer.
Common species: European Redwood, Whitewood, Imported Scandinavian Pine.
About floor joists as a structural member
Floor joists support flooring, partitions and live load (people, furniture). Designed to AS 1684.2 floor joist tables — much heavier loading than ceiling joists.
Common C24 floor joist sizes used in the UK
Section sizes most commonly stocked and specified for C24 floor joists at UK builders' merchants. Maximum allowable spans for each section must be confirmed against TRADA Eurocode 5 span tables.
| Section size (mm) | Typical spacing (mm) | Max single span (m) |
|---|---|---|
| 140×45 | 450 | verify against TRADA Eurocode 5 table |
| 140×45 | 600 | verify against TRADA Eurocode 5 table |
| 190×45 | 450 | verify against TRADA Eurocode 5 table |
| 190×45 | 600 | verify against TRADA Eurocode 5 table |
| 240×45 | 450 | verify against TRADA Eurocode 5 table |
| 240×45 | 600 | verify against TRADA Eurocode 5 table |
| 240×63 | 450 | verify against TRADA Eurocode 5 table |
| 240×63 | 600 | verify against TRADA Eurocode 5 table |
| 240×90 | 450 | verify against TRADA Eurocode 5 table |
| 240×90 | 600 | verify against TRADA Eurocode 5 table |
- 140×45
- Typical spacing (mm)
- 450
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 140×45
- Typical spacing (mm)
- 600
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 190×45
- Typical spacing (mm)
- 450
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 190×45
- Typical spacing (mm)
- 600
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 240×45
- Typical spacing (mm)
- 450
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 240×45
- Typical spacing (mm)
- 600
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 240×63
- Typical spacing (mm)
- 450
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 240×63
- Typical spacing (mm)
- 600
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 240×90
- Typical spacing (mm)
- 450
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 240×90
- Typical spacing (mm)
- 600
- Max single span (m)
- verify against TRADA Eurocode 5 table
Sizing guidance and UK Building Regulations notes
Project-specific sizing guidance is withheld pending qualified review. Ask a qualified designer to assess loads, supports, connections, exposure and the applicable current standard. No size, spacing or span on this reference page is an approved specification.
How to read a C24 floor joist span table (UK)
- Determine your required span — the clear distance between supports.
- Note your spacing — typically 450 or 600 mm centres.
- Identify your loading category (BS EN 1991-1-1 for floors, BS EN 1991-1-3 for snow, BS EN 1991-1-4 for wind).
- Look up the TRADA Eurocode 5 floor joist table for C24 and read off the smallest section whose span exceeds your required span. Confirm with a structural engineer's calculation.
UK timber standards behind C24 sizing
Strength classes for European softwoods are defined in BS EN 338 (Structural timber — Strength classes), with design rules in Eurocode 5 (BS EN 1995-1-1). The legacy UK code BS 5268-2 is still referenced in older tables but Eurocode 5 has been the active design code since 2010. For new-build housing, NHBC Standards Chapter 6.4 (Timber and joinery) sets the practical specification baseline accepted by NHBC, Premier Guarantee and other UK structural warranty providers.