Ceiling joists and binders supporting ceiling joists

Tables 4B.7 to 4B.10 give the maximum clear span of a ceiling joist and the timber binder that provides support to the ceiling joists using timber strength class C16 and C24. See also Diagram 4B.4. The sizes, spacings and spans given will safely support the dead loads stated in the tables, together with a maximum imposed load of 0.25 kN/m² and a concentrated load of 0.9 kN acting together. In calculating the ceiling joist sizes for these tables no account has been taken of trimming around items such as flues or the additional load of such things as water tanks. Notching or drilling of a binder or ceiling joist should not be carried out unless justified by specialist calculation. In the tables for ceiling joists the permissible clear spans are for ceiling joists simply supported between binders or a binder and the wallplate. However, in the tables for binders, the permissible clear spans are based on the assumption that the ceiling joists can be continuous. The section sizes are either sawn across the timber thickness in accordance with tolerance class 1 of BS EN 336 and processed in accordance with tolerance class 2 of BS EN 336 across the timber width (joist depth), or are CLS/ALS processed sizes in accordance with tolerance class 2, to provide level surfaces for ease of ceiling lining and the fixing of structural decking. The size of ceiling joists and binders are limited generally to those where the depth-to-thickness ratio is not greater than 4 unless lateral support is provided in accordance with BS 5268: Part 2.