The floor joist span tables are based on the loadings given in the amended version of BS 6399-1 which is an imposed load of either a uniformly distributed load of 1.5 kN/m² or a concentrated load of 1.4 kN. Joists are to have minimum end bearing of 40mm. Wane as allowed in BS 4978:2007+A2:2017 is permitted in all sections included in these span tables. Proprietary strutting is to be used in accordance with manufacturers recommendations. Solid timber strutting to be at least 38mm thick and be a minimum of three quarters of the joist depth. Joist spans over 4.5m - provide 2 rows of strutting at third span positions.Joist spans 2.5m to 4.5m - provide strutting at mid-span.Joist spans up to 2.5m - no strutting required.Strutting or blocking between joists is required as follows Holes drilled at the neutral axis (centre line) are not to exceed 0.25 of the depth of a joist and are not to be less than three diameters (centre to centre) apart and are to be located between 0.25 and 0.4 of the span from the support. Notches are not to exceed 0.125 of the depth of the joist and are to be located between 0.07 and 0.25 of the span from the support. Timber to be covered, these span tables do not apply to timber which is fully exposed to the elements. The dead loads shown at the top of span table above do not include the self weight of the joists, however, the joist self weights are included (in addition to the dead loads) in the calculations used to determine permissble clear spans. 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 5268-7.1:1990 Structural use of timber - Section 7.1 Domestic floor joists. Dead load per square metre (in kN/m²) supported by joistsĬentre-to-centre spacing of joists (in mm)
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