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  • Writer's pictureJustine Rowbotham-Belot

Project Study: The Imperial Plaza, New Housing From An Old Source, Part I

Imperial Plaza is located at 111 St. Clair Avenue West in Toronto and forms an integral part of the established Wychwood Park community since its construction in 1957. The building was originally designed by Mathers & Haldenby as their entry for Toronto's new city hall design competition. However, the city rejected the design and held an international design competition that was eventually won by Finnish architect Viljo Revell. Imperial Oil purchased the design and moved forward to construct the building as their headquarters with Mathers and Haldenby. 

Design Objectives: 

Maintaining the unique architectural aesthetic of 111 St. Clair West while converting to a state-of-the-art condominium community with over 380 suites, was onespace's central design objective. 

Conversion of such an iconic building required the design team to respect the essential character of the building while elaborating on the quality environment established when mid-century modern design approached its zenith. With its limestone façade punctuated by its distinctive grid-like window treatment, the old Imperial Oil Building is by almost everyone’s reckoning an extremely “robust” structure with a strong emphasis on the vertical. 

To create balconies from the ninth to the seventeenth floor, on the south side of the building required introduction of a second glazed wall facing the present limestone façade and removal of the existing windows. The new balconies lighten the heavy, structured pattern of the building on the south facade.  

Another change visible on the street is the mid-section of the building where the existing mechanical floors previously covered by a series of distinctive opaque glass blocks, were converted into loft apartments, where new floor-to-ceiling window inserts created a decorative effect on the building’s face. 

On the top of the building, the observation level on the 20th floor and the two-story glazed curtain wall mechanical pavilion, above it, were also transformed into truly magnificent three-storey high “townhouses-in-the-sky” with enormous 10’ wide terraces offering stunning vistas over the city. The new glazing—lighter and with a smaller frame size—gives the top of the building a very elegant new look. 

Inside is where the true metamorphosis from office building to luxury condominium is most apparent. The grand entrance lobby was given extraordinary care to ensure that the fundamental integrity of the original design remained intact. This included preservation of the entrance vestibule and two-storey high lobby, marble flooring, the York Wilson murals (The Story of Oil), and three original clocks which were each rehabilitated to full working order.  

Imperial Plaza’s transformation was deemed an immense success as, quite literally, the man on the street doesn’t notice that the building has changed much. 


Given the threat of the Cold War in the 1950’s and the building’s relative distance from the downtown core, the building was intended to function as a hospital in the event of a nuclear attack. This additional municipal responsibility resulted in additional measures for protection in the form of thick exterior walls and small windows for all above-grade levels. In addition, the limestone exterior finish was deemed of historical significance and could not be altered. The existing openings could be utilized but new penetrations were not permitted in the existing limestone cladding. New replacement windows were designed with continuous louvers at the header to achieve mechanical requirements for residential occupancy required by the code. 

Onespace worked closely with Heritage Toronto to ensure that the replacement windows matched the appearance of the existing frames. The original window frames were a matt aluminum finish which had become pitted and discoloured over time, so the replacement window frames were chosen to closely match the weathered effect. 

The principal challenge was creating attractive residential units within the existing steel-framed structure, while ensuring that the layouts did not interfere with the steel columns and beams. 

When originally constructed, it was decided not to use the very noisy practice of riveting the building’s steel frame together and instead it was welded making it the largest welded frame building in the world. The approach resulted in a very robust structural frame that was required to remain intact and without modification. All suites were therefore designed to adapt to the column spacing and placement as they occurred and took advantage to showcase and preserve the character of the building when the opportunity became available.  

The existing floor system assembled from hollow core precast concrete slabs was treated in similar fashion. Great care was taken during the renovation process to precisely locate new vertical shafts for plumbing and sprinkler lines to avoid weakening the structural integrity of the floor system. This process was challenged by those purchasers who requested relocation of plumbing for washrooms and kitchens based on personal requirements. 

The exterior alterations, including window replacement and the careful insertion of terraces, were designed to have a minimal impact on the robust and clean lines of the original stone exterior. 

The demolition and removal of the mechanical equipment located within the three basement levels was a lengthy process but ultimately opened opportunities for repurposing of the space. The lower two levels were converted to parking and other necessities while the first basement level was outfitted as the building’s new indoor amenity space featuring music recording/rehearsal sound studios, a golf simulator, a gaming room, and full-sized fitness club with opulent change rooms, squash courts, yoga and aerobics studios. In addition, a spa inspired swimming pool and hot tub were added making the amenity space of the building amongst the largest available in new residential condominium projects. 

Part II to follow.

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