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Heritage envelope rehab a balancing act

Dan O'Reilly
Heritage envelope rehab a balancing act

Rehabilitating the exterior envelopes of Canada’s historic buildings without altering the elements which make them historic is a major balancing act requiring intensive preconstruction planning and investigative work, participants at a Construct Canada seminar were told.

There are 9,000 listed heritage buildings in Toronto alone, of which 4,500 are designated under the Ontario Heritage Act and 3,500 have federal government designation, said guest speaker Sarah Gray, a managing principal with the consulting engineering firm Halsall Associates.

A building scientist and a member of the Canadian Association of Heritage Planners, Gray explained there are differences in meanings for terms such as "restoration, rehabilitation, conservation, and preservation."

"Restoration would be removing vinyl siding to reveal the wood underneath. Preservation is protecting, maintaining and/or stabilizing the existing materials of an historic place while protecting its heritage value."

On the other hand, rehabilitation makes possible "a continuing or compatible contemporary use of a historic place or individual component while protecting its heritage value. It can include repairing or replacing."

And for a rehabilitation to be successful, the various project partners have to work together so they can understand the building and intelligently respond to issues posed by the project.

As described by Gray, rehabilitating historic building envelopes is as much detective work as it is building science.

"We liked to dive right in," said Gray, explaining one of the first steps in the process is reviewing the original drawings, even if they weren’t complete, as well as other documents that can provide valuable information to its construction. Early photographs are also extremely helpful.

"Even in 1918 engineers and material scientists did tests," said Gray, who showed a Powerpoint slide of tests conducted at that time on the former Dominion Bank Building in Toronto, now part of the One King West condominium hotel.

(A few years ago a comprehensive hands-on inspection of the building’s façade was conducted by the investigation and testing firm, Vertical Access in collaboration with Halsall Associates).

A variety of strategies and tests are used to detect material defects such as cracks, masonry spalling, and corroded steel. These include short and long-term monitoring, mocks ups, trial repairs, thermal imaging, and inspection by firms such as Vertical Access, she said.

Also, there are always a number of repair options which can be recommended.

But ultimately the option chosen is determined by the owner and the budget available.

"We always have to keep the clients’ objectives in mind. It’s always a question of money."

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