London planners gave the thumbs up to redevelop a 1991-constructed city office building at 60 London Wall at the start of the year.
Enabling works are now underway and Skanska is expected to start work on the Moorgate building project towards the end of the year.
The existing office will be stripped back to its steel frame and rebuilt with an extra four floors raising the total office space to 320,000 sq ft.
Designs by architect EPR see the upper five floors of the 12-storey building stepped and set back from the front elevation lessening their impact at street level and creating outdoor space for terraces.
LaSalle Investment Management bought the 260,000 sq ft building for just under £200m last summer on behalf of California State Teachers’ Retirement System.
Gary Player, Head of London Business Space, LaSalle Investment Management commented: “We acquired 60 London Wall because of its prime location in an area that is becoming more accessible, with Crossrail/Elizabeth line, as well as the opportunity to create significant additional lettable area and a first-class product that we will be delivering in 2019.”