These actions are more difficult to determine accuratelly. For many of them, it is only possible to make conservative estimates based on standard codes of practice or past experience. Examples of variable actions on buildings are: the weights of its occupants, furniture, or machinery; the pressures of wind, the weight of snow, and of retained earth or water; and the forces caused by thermal expansion or shrinkage of the concrete.
A large building is unikely to be carrying its full variable action simultaneously on all its floors. For this reason EN 1991-1-1:2002 (Actions on Structures) clause 6.2.2(2) allows a reduction in the total variable floor actions when the columns, walls or foundations are designed, for a building more than two storeys high. Similarly from the same code, clause 188.8.131.52(10), the variable action mat be reduced when designing a beam span which supports a large floor area.
Although the wind load is a variable action, it is kept in a separate category when its partial factors of safety are specified, and when the load combinations on the structure are being considered.