Tower 42 - History - Construction

Construction

Demolition of the site commenced in 1970 and the tower was completed in 1980. The building was constructed by John Mowlem & Co around a huge concrete core from which the floors are cantilevered, giving it great strength but significantly limiting the amount of office space available.

In total, there are 47 levels above ground, of which 42 are cantilevered. The lowest cantilevered floor is designated Level 1, but is in fact the fourth level above ground. The cantilevered floors are designed as three segments, or leaves, which approximately correspond to the three chevrons of the NatWest logo when viewed in plan. The two lowest cantilevered levels (1 and 2) are formed of a single "leaf"; and the next two (3 and 4) are formed of two leaves. This pattern is repeated at the top, so that only levels 5 to 38 extend around the whole of the building.

The limitations of the design were immediately apparent - even though the building opened six years before the Big Bang, when there was a lesser requirement for large trading floors, the bank decided not to locate its foreign exchange and money market trading operation ("World Money Centre") into the tower. This unit remained in its existing location at 53 Threadneedle Street. Other international banking units, such as International Westminster Bank's London Branch and the Nostro Reconciliations Department remained at their locations (at 41 Threadneedle Street and Park House, Finsbury Square, respectively) due to insufficient space in the tower.

Innovative features in the design included double-decked elevators, which provide an express service between the ground/mezzanine levels and the sky lobbies at levels 23 and 24. Both the concept of double decked elevators and sky lobbies were new to the UK at the time. Other innovative features included an internal automated "mail train" used for mail deliveries and document distribution; an automated external window washing system; and computer controlled air conditioning. The tower also had its own telephone exchange installed in one of the basement levels – this area was fitted with panoramic photographs of the London skyline, creating the illusion of being above ground.

Fire suppression design features included pressurised stairwells, smoke venting and fire retardant floor barriers. However, at the time of design, fire sprinkler systems were not mandatory in the UK and so were not installed. It was this omission, coupled with an onsite fire at the tower during the 1996 refurbishment, that prompted the Greater London Council to amend its fire regulations and require sprinkler installations at all buildings.

The cantilever is constructed to take advantage of the air rights granted to it and the neighbouring site whilst respecting the banking hall on that adjacent site, as only one building was allowed to be developed. For a time it was the tallest cantilever in the world.