Check out this duplex in Ottawa. 3000 sq f at $251US a sq f. LEED Platinum and it qualifies as the first residential Passivhaus in Canada. The slideshow is long, but a good illustration of two things: duplex redevelopment on single family lot and Passivhous design/build from empty lot. At $251/ft2 it would make each duplex cost $376,500 USD, which is roughly on par with CAD$ right now. Factor in the increased building costs of BC, you could still build each side of this duplex for under $450K. The lots in the Lower Cap are at least big enough for this, if not more and the redevelopment costs mean that the duplex units would even be affordable. Now the only way this would work is if current owners chose to redevelop themselves or in partnership with neighbours. If you rezoned first and then sold to a developer at duplex lot value the economics would not, as Jay points out, work.