I think his point is a fair one, though, I might have an issue with providing only 1 elevator in a building. What if someone using a mobility aid lives above the ground floor? I'm ok w/entirely walk-up buildings, but the moment you make it possible and legal for someone w/mobility impairment to live off the ground, you need to answer the question "What happens when the elevator is broken or requires maintenance?"
I've seen this issue come up in buildings with 2 elevators, both out of service at the same time............so the risk with one elevator may be rather acute.
Obviously, as well, removing the 2nd staircase requirement needs to be paired with other regulation, such as mandating sprinklers or other fire suppression.
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To me, a reasonable move would be immediately lifting the standard to 3 floors in the Federal Building Code (this would harmonize our rules with the U.S. which often carries weight w/officials in Ottawa), then examining under what circumstances one might be able to do so at 4 or 5 floors.