425 Viger West

  • 425 Viger

Client: Allied REIT
Award :

The project consisted in extending ten existing floors located on the North-East corner of a building dating back to 1910 in which each floor extension has an area of 475 m² (5,100 ft²). Moreover, three additional floors in lightweight steel of 1,625 m² (17,500 ft²) each are also added on top of the existing project. In its new configuration, the building offers 30,100 m² (324,000 ft²) of office space.

The seismic retrofit of the structure was accomplished using three new cores housing stairwells and six elevators.

One of the main challenges was the integration of the new concrete cores and elevator pits at the foundation level since the new raft foundations had to be integrated to the existing foundations. In order to allow for the under-pinning work to be realized, temporary shoring systems were developed that suspended 12 existing columns in mid-air bearing 10 storeys each. The columns were supported on steel tripods using drilled pile foundations that were also designed to support the additional load of the three new steel floors on the roof.


  • Transformation of a centennial building braced by non-reinforced brick masonry.
  • Addition of 3 floors on existing foundations without reinforcement of columns or foundation.
  • Integration of a reinforced concrete bracing system into the existing structure.
  • Management of construction phases; assembly of the roof steel frames before the installation of the new bracing walls.


  • Underpinning of 12 columns supporting a total of 13 storeys each for the construction of the raft foundations of the 3 new bracing cores.
  • Design of the seismic junctions between the new structure and the existing building.
  • Sequencing of the construction to maintain the stability of the existing building.
  • Mixed use of existing structures, steel and reinforced concrete.

To visit the project via Google Street View...


  • Travaux de soutènement
  • P1
  • P2
  • P3
  • Acier-1
  • Acier 2
  • Acier 3