![]() Joists supporting additional loads should be calculated by a competent person. These span tables make no additional allowance for partitions or any other loads additional loads. BS 5268-7.1 was published before BS 6399-1 was amended to include the more onerous 1.4 kN imposed concentrated load, so the approach adopted for these span tables uses the recommendations given in BS 6399-1, however, both approaches do result in similar joist sizes being calculated. Overhang Span.Sometimes referred to as cantilever, overhang is the distance from the face of the support to the free end of the beam, measured along the beam as illustrated. ![]() ![]() Other span tables are based on the guidance given in BS 5268-7.1 which is a uniformly distributed load of 1.5kN/m² for spans greater than 2400 mm and 3.6 kN load per metre width of floor for spans less than 2400 mm to ensure that very small joist sizes do not result from the calculations for smaller spans. However if either of the above conditions are not met, use the single span tables for the purpose of obtaining the appropriate size. 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. The depth of the bridge should be at least ¾ the depth of the joist. Where a span is greater than 2.7m, bridging is required at 1.35m centres. 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. the height that all deviations are to be related to is known as the target size. Timber to be covered, these span tables do not apply to timber which is fully exposed to the elements. Treatment + All LVL distributed by Lumberbank will be treated with the innovative Lonza AZOTEK treatment to H1.2. 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. Chamfers for counter beams, hanging beams and strutting beams may be 17.5deg to a minimum remaining depth of 1:3 or 100mm. 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. Where strutting beams occur over openings, the lintels have to be designed for a concentrated load.Dead load per square metre (in kN/m²) supported by joistsĬentre-to-centre spacing of joists (in mm) They bear directly above studs supporting concentrated loads or distributed over two or more studs by means of top plate stiffening. Strutting beams may extend in any direction in the roof space. This clearance is between the underside of the beams and the tops of ceiling joists, ceiling lining or ceiling battens, as appropriate. Blocking should be provided between strutting beams and wall plates to provide an initial clearance of 25 mm at mid-span. The ends of strutting beams must bear on the full width of wall plates. This means they may move up and down or from side to side, causing the ceiling to move and possibly crack. Also, they transfer roof loads that are often dynamic because of wind pressure acting on the roof. This is because they are likely to sag and will cause the ceilings to sag. Strutting beams cannot double as hanging beams. It must never rest on, or transfer load to, a ceiling joist. The strutting beam transfers the roof load directly to load bearing walls. Their function is always to support roof members, generally below the underpurlins, where there are no conveniently located load-bearing walls. 'Strutting' beams are used in many ways and locations in a conventionally framed roof.
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