Class 2B buildings – ties or notional removal checks

For a Class 2B building either (a) or (b) should be followed – (a) provide effective – (i) horizontal ties, as described in the codes and standards listed under paragraph 3.8 for framed and load-bearing wall construction; (the latter being defined in paragraph 3.11); and (ii) vertical ties, as defined in the codes and standards listed under paragraph 3.8, in all supporting columns and walls; or (b) check that upon the notional removal of each supporting column and each beam supporting one or more columns, or any nominal length of load-bearing wall (one at a time in each storey of the building) that the building remains stable and that the area of floor at any storey at risk of collapse does not exceed 15% of the floor area of that storey or 100 m2, whichever is smaller, and does not extend further than the immediate adjacent storeys (see Diagram 3.1). Where the notional removal of such columns and lengths of walls would result in an extent of damage in excess of the above limit, then any such element should be designed as a "key element" as described in paragraph 3.10.