The stone face of the Bank of Canada headquarters, completed in 1938 on Ottawa’s Wellington Street, is classicism shaved bare, a blank stare, a block of grey stoicism to suggest that an impenetrable bank is a good bank.

Then, with the looser democracy of wide lapels and wide floor plans, came Arthur Erickson’s 1979 extension. It goes for exactly the opposite effect. Two 12-storey glass towers, rising from behind the old bank, are all about openness and transparency, a central bank for the populace, more or less.

And connecting the towers is the once-public atrium of indoor naturalness – for many years a water pond, foliage, that kind of thing – not the indoor Canadian landscape that Mr. Erickson might have preferred, but ferns, bamboo, succulents, the kind of plants that survive in malls, and a horizontal, wooden trellis to suggest the bridging of the country’s east and west.

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Still, despite being a little underused by B of C staff, functioning instead primarily as a walkway between the two towers, and a nice spot for wedding photos when it was still open to the public, the atrium provided a much needed reprieve from the surrounding stone and glass. As with Mr. Erickson’s Robson Square in Vancouver and the Simon Fraser University campus in Burnaby, much of the late architect’s greatness was the dialogue he created between nature and modernism. And the possible loss of the atrium garden had conservationists particularly worried prior to the bank headquarters’ three-year, $460-million full-scale renovation, which was completed last year.

The conservationists’ concerns serve as a key lesson for any institution or company debating how to go about renovating or rebuilding its headquarters. In the end, the atrium was saved, but redesigned, and Bank of Canada staff have moved back into the property.

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A view in Ottawa looking down on the Bank of Canada atrium, with the 1938 building at top, and the 1979 Arthur Erickson glass towers on the other sides.

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“That was definitely a lesson learned. And I tell this to all my clients now: You might not think a building has particular merit, but other people do,” said Andrew Frontini, principal and design director at the architecture firm Perkins + Will Canada, the lead designers of the Bank of Canada renovation. “If we don’t do due diligence, recognizing its significance, documenting it and doing a proper assessment of what has heritage value and what doesn’t, then we’re all going to be sorry.”

Heritage renovations are about more than just the needs of tenants and landlords, restoration costs or even aesthetics. “What has heritage value and what doesn’t is being redefined every day. So you have to be aware of that. If someone has decided this is important, and you didn’t, then you’ve desecrated it. That’s the danger,” Mr. Frontini said.

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The original stone face of the Bank of Canada in Ottawa, with its modern glass-tower additions. The entire property has been given a makeover.

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The Royal Architectural Institute of Canada and the National Trust for Canada (formerly known as Heritage Canada The National Trust), as well as key heritage advocates such as Phyllis Lambert, founder of the Canadian Centre for Architecture, had publicly expressed strong concerns, back when the bank’s design plans were still in the works, particularly about changes to the atrium and the possible removal of the garden, as well as the decision to close it to the public as security needs have changed since Mr. Erickson’s day.

Ms. Lambert wrote in a letter to Bank of Canada Governor Stephen Poloz, “The plans for the bank do not preserve the architectural heritage and integrity of the building. They desecrate it.” As one of the few, key campaigners for the buildings that create Canada’s sense of place and history, her voice, along with those of other conservationists, resonates throughout the architectural community.

“When they are historic buildings, people’s radar is up. They want to make certain that they are handled well,” said architect and conservation expert Julia Gersovitz, a founding partner at EVOQ, which was heritage consultant on the Bank of Canada project. In effect, the controversy was due to the bank now having to balance the openness and transparency of the 1970s extension and the atrium with at least a small return to the higher security, safebox sensibility of the 1930s building.

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“That generosity of intent [with the previously public atrium] came under question because of the increasing security climate everywhere in the world,” Ms. Gersovitz said.

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While the atrium is now closed to the public, the garden was altered to allow more room for Bank of Canada staff to meet and sit among the plants.

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The bank’s chief operating officer, Filipe Dinis, indicated that the bank was open to input from the conservationists. “What was really important for us was recognizing that these communities are key stakeholders. So it was an opportunity for us to listen and seek input from the experts and factor those considerations into our ultimate design plan,” Mr. Dinis said in a recent interview.

But it was a balancing act. There are hints that during the renovation-design stage, the bank wasn’t too keen to defer any decision-making authority, primarily because its budget for the new headquarters was unbudgeable. “We had a fixed price, $460-million ... from the beginning,” the bank’s Mr. Dinis noted.

“Every decision that was made always went through that lens,” said Mr. Frontini, the architect. “But what was interesting was that [staying on budget] was a must-have, but then the other must-have was that we can’t risk some kind of public relations nightmare because we desecrated the work of Canada’s most famous architect – because that would be seen as wasting taxpayers’ money as well.”

So, “we went to the bank and said, ‘We think what you need to do is engage this community that you haven’t wanted to engage,’ ” Mr. Frontini said.

Of utmost importance were urgently needed upgrades. There were no sprinkler systems, nor sufficient seismic safeguards, despite Ottawa sitting on a significant seismic zone. There were continual problems with the atrium garden, water seeping into the basement, water and air quality issues due to too much chlorine or sometimes not enough.

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Human nature had also kicked in. Mr. Erickson’s open-concept work floors were millennial-ready decades before millennials were even born. But over the years, makeshift office partitions had been erected, ugly improvisations, a rabbit warren, said Mr. Frontini, and temperature control all along the glass facade was terrible. The original 1930s building had become an exercise in misplaced drywall, while school kids visiting the Bank of Canada museum in the basement were treated to institutional humdrum.

Interior features such as Mr. Erickson’s waffle-pattern ceilings on each floor of the towers were kept, but reinforced, along with the elevator shafts. “So, literally the building was temporarily stabilized. All of the elevators and stairs in the middle of the building were surgically demolished, and then repoured with a lot more reinforcement inside,” Mr. Frontini said. Ventilation was improved with new glass panels all around the inside, so as not to alter the look of Mr. Erickson’s glass exterior. The interior of the 1930s building was meticulously restored, as much as possible, to its original state. The museum is now situated below an adjacent outdoor plaza, with a much more welcoming, naturally lit entrance.

Yet, although the atrium is now closed to the public, the garden was altered to allow much more room for the bank’s staff to meet and sit among the plants. And what relieved the conservation community most, it seems, was a charrette, a meeting between the bank and contemporaries of Mr. Erickson, notably architect Keith Loffler who had worked on the 1970s extension and the venerated landscape architect Cornelia Oberlander. They gave very specific ideas, especially to improve the atrium plans.

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The museum of the Bank of Canada is now situated below an adjacent outdoor plaza, with a much more welcoming, naturally lit entrance.

DOUBLESPACE PHOTOGRAPHY/Handout

“They saw their participation in the charrette as both looking toward the history, but also looking forward as a design problem,” Ms. Gersovitz said. “I found the whole experience extraordinarily interesting.”

“I think we did a better job because of that process of involving Cornelia [Oberlander] and Keith Loffler,” Mr. Frontini said. Getting their input wasn’t a cynical response, he said, but helped to focus the project. It forced the bank to finally choose among the many different design options that the architects had produced for the atrium. “It helped generate solutions. Everybody was happy,” Mr. Frontini said.

Editor’s note: Due to an editing error, an earlier version of this story incorrectly identified the Department of Canadian Heritage as having concerns about the bank’s design plans. The correct organization is the National Trust for Canada (formerly known as Heritage Canada The National Trust.)