January 26, 2012

PETER KENTER

A five-storey network of steel supporting the north facade of the Five Condos project, in downtown Toronto, has proven to be a dramatic sign of construction in the area. When completed, the project will result in a 45-storey building which will feature a sleek glass and steel design by Hariri Pontarini Architects.

FEATURE | Steel

Network of steel supports preservation at Five Condos construction site in Toronto

PETER KENTER

correspondent

Downtown Toronto’s 45-storey Five Condos, near Wellesley and Yonge streets, will feature a sleek glass and steel design by Hariri Pontarini Architects.

The building streetscape, however, is rooted in the past with the preservation of historically protected construction details.

With the building’s foundation now under excavation, the most dramatic sign of construction is the five-storey network of steel, supporting the building’s north facade along St. Joseph Street.

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The historic preservation of the building was completed under the guidance of heritage specialist E.R.A. Architects Inc. of Toronto.

“The intent is to preserve some really nice brickwork,” says E.R.A. principal Scott Weir.

“The main central arch is of a size and quality that would be difficult to reproduce, so that section needed to be held in place while the excavation went down a number of floors behind it to a depth of about 19 metres.”

The steel support was devised by geostructural engineer Brian Isherwood of Isherwood and Associates of Mississauga.

“It’s probably one of the largest shoring systems of its kind in the city,” says E.R.A. architect Ryan Love.

“The initial design we presented to the city was probably half the size of the final structure.”

But design of the steel support structure was complicated by a number of factors, including the location of existing utilities, construction vehicle access, and the triangulation required to properly support the wall.

“Once they had mapped out all of the utilities, the base of the support had extended far into St. Joseph Street,” says Love. “At that point they bumped it out just a little farther so that there was enough room in the lower portion for construction vehicles and delivery trucks to drive underneath the support.”

The support is made of steel girders and was constructed over the space of a month under the supervision of heritage masonry specialist Paul Goldsmith, president of Historic Restoration, Inc.

“There was a lot of tweaking of the design,” notes Weir.

“Movement can occur in the bricks over the length of the construction, so the steel was threaded through the wall in locations near the base and other areas where a single stone could be removed and later replaced. That limits the need for extensive repair when the structure is removed.”

The ultimate configuration was a structure 17 metres high and three metres deep. Diagonal members of the support reach out to the middle of the street where they’re anchored into a large concrete base.

Micropiles anchor the structure to the substrate below, small enough to negotiate the restricted spaces between gas, phone, cable, electric, water and sewage utilities. The back of the wall has been sandblasted, then draped with polyethylene sheeting to protect it from the weather and construction work.

As the condominium rises to the fifth floor, the east wall of the historic building will be rebuilt from material salvaged during demolition. As construction proceeds above the facade and the historic elements are tied into new construction, the steel support will be removed.

A row of retail buildings along Yonge Street was also purchased outright by the developers, Graywood Developments Ltd. and Mod Developments Inc., to ensure the condominium building would be flanked on the east side by heritage properties that will help retain the familiar streetscape.

“I think it’s a credit to the developers that they went through the effort and expense to preserve these historic elements with such care,” says Weir.

“Even the steel support structure is beautiful. It cost them a huge amount to pay for the support and the temporarily lost parking to the city, compared to simply demolishing the building, but the end product is a nice heritage project.”

Digital Media Editor's Note:

Daily Commercial News subscribers may view more information the Five Condos project by viewing project ID 9114748 in Reed Construction Data Canada Building Reports. More information on ERA Architects can be found by viewing company ID 180446.

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