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Joist Span Tables — C16 and C24 Timber
Maximum clear spans for C16 and C24 domestic floor joists at 400mm and 600mm centres, calculated to BS EN 1995-1-1 (Eurocode 5) with UK National Annex parameters.
C16 Floor Joists — Dead Load 0.25-0.50 kN/m²
Domestic floor, imposed load 1.5 kN/m² plus a separate 2.0 kN concentrated-load check (residential category A, BS EN 1991-1-1). Sizes shown are nominal sawn; the calculations use the regularised finished sections to BS EN 336 (47 x 100 computes as 45 x 95, 47 x 200 as 45 x 195, and so on).
| Joist Size (mm) | 400mm Centres (m) | 600mm Centres (m) |
|---|---|---|
| 47 x 100 | 1.71 | 1.46 |
| 47 x 125 | 2.16 | 1.86 |
| 47 x 150 | 2.62 | 2.28 |
| 47 x 175 | 3.07 | 2.68 |
| 47 x 200 | 3.52 | 3.07 |
| 47 x 225 | 3.97 | 3.47 |
| 75 x 200 | 4.07 | 3.60 |
| 75 x 225 | 4.44 | 4.03 |
C24 Floor Joists — Dead Load 0.25-0.50 kN/m²
Same loading conditions as above, higher strength grade.
| Joist Size (mm) | 400mm Centres (m) | 600mm Centres (m) |
|---|---|---|
| 47 x 100 | 1.91 | 1.62 |
| 47 x 125 | 2.42 | 2.09 |
| 47 x 150 | 2.92 | 2.55 |
| 47 x 175 | 3.42 | 2.99 |
| 47 x 200 | 3.93 | 3.43 |
| 47 x 225 | 4.30 | 3.87 |
| 75 x 200 | 4.40 | 3.99 |
| 75 x 225 | 4.81 | 4.37 |
Dead Load Categories
| Category | Dead Load (kN/m²) | Typical Construction |
|---|---|---|
| Light | < 0.25 | Chipboard deck only, no ceiling |
| Medium | 0.25 – 0.50 | Chipboard + plasterboard ceiling + standard finishes |
| Heavy | 0.50 – 1.25 | Tiles on screed, heavy boarding, sand/cement screed |
Basis of These Tables
- Imposed load 1.5 kN/m² plus a separate 2.0 kN concentrated-load check (residential category A, BS EN 1991-1-1).
- Dead-load band up to 0.50 kN/m² excluding joist self-weight, which the calculation adds separately.
- No partition allowance is included. Where any partition bears on or crosses these joists, add the BS EN 1991-1-1 partition allowance or have the floor checked by a structural engineer.
- Deflection is limited to the stricter of span/333 and 12 mm.
- A minimum end bearing of 40 mm is assumed at each support.
- Values are rounded down to 0.01 m.
Span values calculated by TradeCalculator to BS EN 1995-1-1 (Eurocode 5) with UK National Annex parameters for the stated load case, and cross-checked against published industry span tables. Always confirm sizing with a structural engineer, particularly for unusual loading or non-standard conditions.
Related Pages
See the UK Timber Sizes reference, the Rafter Span Tables, the Notching and Drilling Rules, and the Timber Span Calculator.
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Last updated: April 2026
Verified against UK standards · estimates only, confirm with your supplier.