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 5268-7.2:1989 Structural use of timber - Section 7.2 Joists for flat roofs. * Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4 Dead load per square metre (in kN/m²) supported by joistsĬentre-to-centre spacing of joists (in mm)