The current Approved Document A, for England and Wales was published in June 2004 and came into effect from December 2004. The overall objective of the changes are to improve the standards of safety for persons in or about buildings. It also gives guidance on loading and ground movement.

One of the changes in the current document is the removal of the application limit to requirement A3. Buildings of less than 5 storeys are now included with benefit to public safety. The guidance given in the document gives clear advise on the measures that may be taken to meet the requirement.

A3: Disproportionate collapse

“The building shall be constructed so that in the event of an accident the building will not suffer collapse to an extent disproportionate to the cause.”

The guidance deals with the means of reducing the sensitivity of a building to disproportionate collapse in the event of an accident. The structures are divided into categories depending on the risk factor and the consequences of an accidental failure.

These parameters depend on the type of the building, the likelihood of accidents and the number of people that may be affected. These are categorised by consequence class as shown in Table 1.

Table 1: Building classes (based upon Approved Document A, 2004 Edition, Table 11)

2004 structure

NOTE 1: For buildings intended for more than one type of use the Class should be that pertaining to the most onerous type.

NOTE 2: In determining the number of storeys in a building, basement storeys may be excluded provided such basement storeys fulfill the robustness requirements of Class 2B building