The use of Steel Beams are not required for every Building Regulation application but usually for:
The removal of an internal loadbearing wall.
The support of a roof, or the support of an external cavity wall when 'knocking through' from the existing dwelling into an extention.
The support of floor timbers and existing roof structure when carrying out a loft conversion to either a house or a bungalow.
The support of the roof structure when installing a 'vaulted' ceiling.