The first of 4,500 steel sections was installed by the firm late last month and the building’s envelope is already up to the fourth floor.
Hare started on site exactly one month ago to build the steel envelope around the 38-storey concrete core constructed by PC Harrington.
The latest computer modelling techniques are being used to construct the Walkie Talkie’s superstructure for clients Land Securities and Canary Wharf Group.
The 160 metre high building flares outwards from its base so that the larger floorplates are to be found at the higher storeys.
Harrington has poured 21,000 cubic metres of concrete to form the foundations and core which also contain 5,000 tonnes of steel.
When complete, 20 Fenchurch Street will contain over 28,000 cubic metres of concrete, 13,000 tonnes of structural and reinforced steel and approximately 33,000m2 of glass.
Hare is fabricating all the steel at factories in Bury, Scarborough and Wetherby.
The skyscraper is due for completion in early 2014.
Cormac MacCrann, Executive Director of main contractor Canary Wharf Contractors Limited, said: “Just a year into construction, 20 Fenchurch Street is already an exciting addition to London’s skyline.”