ABSTRACT
The thickness of joists, by this method, is usually standardized at 50 mm. The nearest commercial size, therefore, would be 225 50 mm.
8.1.4 Structurally Graded Timber By comparison, table A1 for floor joists, given in The Building Regulations’ AD (approved document) A1/2, specifies joists of 220 38 mm section at 400 mm centres, for a maximum span of 4.43 m. However, it should be noted that SC3 (strength class 3 – now referred to as C16) structurally graded timber is specified. Such timber is now commonly relied upon for structural uses and is covered by BS 4978 – and BS 5268: Part 2: 1991. Certain standards and criteria are laid down regarding the size and position of knots, the slope of grain, etc., and the assigning of species and grade combinations to strength classes SC3 (C16) and SC4 (C24).
