Date Published 1 July 2023 Document Type Timber Knowledge Sheet Category Design Audience Architect | Designer | Engineer | Specifier Theme Span Tables Author Bartosz Belch for TDUK
The following span tables indicate the required size of C24 strength class timber members for common uses.
| C24 Span Table - Domestic Ceiling Joists Imposed load not exceeding qk = 0.25 kN/m2 and Qk = 0.9 kN. | |||||||
| C24 | Dead load per square metre excluding weight of joist | ||||||
| Dead load not more than 0.25 kN/m2 | Dead load not more than 0.5 kN/m2 | ||||||
| Centre-to-centre spacing of joists | |||||||
| Joist size (breadth x depth) |
400 mm | 450 mm | 600 mm | 400 mm | 450 mm | 600 mm | |
| Imperial Sizes | Actual Metric Sizes | Maximum clear span in metres | |||||
| 4 x 2 CLS | 38mm x 89mm | 1.75m | 1.72m | 1.67m | 1.65m | 1.62m | 1.55m |
| 6 x 2 CLS | 38mmm x 140mm | 3.15m | 3.09m | 2.95m | 2.92m | 2.86m | 2.70m |
| 8 x 2 CLS | 38mm x 184mm | 4.39m | 4.31m | 4.09m | 4.04m | 3.94m | 3.70m |
| 10 x 2 CLS | 38mm x 235mm | 5.85m | 5.72m | 5.40m | 5.34m | 5.20m | 4.87m |
| 4 x 2 | 45mm x 95mm | 2.06m | 2.03m | 1.95m | 1.93m | 1.90m | 1.81m |
| 5 x 2 | 45mm x 120mm | 2.78m | 2.73m | 2.62m | 2.59m | 2.54m | 2.41m |
| 6 x 2 | 45mm x 145mm | 3.52m | 3.46m | 3.29m | 3.26m | 3.19m | 3.01m |
| 7 x 2 | 45mm x 170mm | 4.27m | 4.19m | 3.97m | 3.93m | 3.84m | 3.61m |
| 8 x 2 | 45mm x 195mm | 5.02m | 4.92m | 4.65m | 4.60m | 4.49m | 4.21m |
| 9 x 2 | 45mm x 220mm | 5.76m | 5.64m | 5.33m | 5.27m | 5.14m | 4.81m |
| 5 x 3 | 72mm x 120mm | 3.37m | 3.31m | 3.16m | 3.12m | 3.06m | 2.89m |
| 6 x 3 | 72mm x 145mm | 4.22m | 4.14m | 3.94m | 3.90m | 3.81m | 3.59m |
| 7 x 3 | 72mm x 170mm | 5.08m | 4.98m | 4.72m | 4.67m | 4.56m | 4.29m |
| 8 x 3 | 72mm x 195mm | 5.93m | 5.81m | 5.50m | 5.44m | 5.30m | 4.98m |
| 9 x 3 | 72mm x 220mm | 6.76m | 6.63m | 6.27m | 6.19m | 6.04m | 5.67m |
| 8 x 4 CLS | 89mm x 184mm | 5.96m | 5.85m | 5.54m | 5.48m | 5.35m | 5.03m |
| 10 x 4 CLS | 89mm x 235mm | 7.74m | 7.59m | 7.19m | 7.11m | 6.94m | 6.51m |
| The above table provides a general summary of common permissible clear spans of simply supported domestic ceiling joists of solid timber for specified loadings, sizes and spacings. The table is solely for guidance on the loadbearing capacity of solid timber members, and cannot be adapted for hardwoods or engineered timber products. In preparing this table, Timber Development UK has assumed the complete design and build will be delivered by competent people and that thorough engineering calculations will be undertaken to verify the guidance provided above for each specific circumstance. |
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The above table is provided by the Timber Development UK organisation. Nottage Joinery Ltd (Trading as Nottage Timber Merchants) accept no responsibility for its accuracy.
The allowable clear spans have been calculated in accordance with BS 5268-2:2002 Structural use of timber - Part 2: Code of practice for permissible stress design, materials and workmanship and BS 5268-7.3:1989 Structural use of timber - Section 7.3 Ceiling joists.
When calculating the Dead load weights; do not include the weight of the joists. The weight of the joists is factored into the total dead weight load. This does not need to be calculated separately.
These span tables do not apply other applications of joists. This is for Domestic Ceiling Joists ONLY
Ceiling joists may be continuous or made up of shorter lengths joined at intermediate supports such as binders.
Holes and notches for electrical or plumbing must not be drilled or cut into the timber joists unless calculations showing the modifications has been proved adequate by specialist calculations.
This table is for internal work only. Timber must be covered, and protected from the elements. This span table do not apply to timber which is fully exposed to the elements.
Wane (Bark inclusion) as allowed in BS 4978:2007+A2:2017 is permitted in all sections included in these span tables.
Joists are to have minimum end bearing of 40mm.
These span tables are based on the imposed loads given in BS 5268-7.1 and BS 6399-1, with an imposed uniformly distributed load of 0.25kN/m² acting together with a concentrated (point) load of 0.9 kN.
These span tables make no additional allowance for water tanks or any other additional loads. Joists supporting additional loads should be calculated by a competent person.