I'm not aware of any comparisons or cost-benefit analyses done of keeping an existing building versus tearing it down to build a more highly efficient building. I certainly don't want to speculate on what the Canadian Commission on Building and Fire Codes might look at, but when they do look at the energy codes for new buildings and existing buildings, perhaps that's some kind of consideration that would be looked at, in that context.
On February 6th, 2018. See this statement in context.