Mike,
I never said homes have to be LEED platinum. I recognize that achieving that level of certification would be an expensive proposition. But surely our cities can require that all new multi-storey dwellings require LEED-H certification (lowest level) just like Miller's plans for homes in Toronto:
http://dcnonl.com/article/id28782
In fact, I'd probably go further and demand that all buildings meet LEED certified minimum. This is not so much of a stretch when there are cities in the US that are demanding that all new multi-storey construction meet LEED Silver or Gold.
As to the argument about cost. Most analysts agree that LEED certification only adds between 1.5% - 3% to the cost of building a certified building:
http://www.cleanair-coolplanet.org/for_communities/LEED_links/AnalyzingtheCostofLEED.pdf
I really don't think home ownership and affordability would tumble if builders added that much at once. Miller added just as big an increment with his land transfer tax in one shot. Moreover, occupiers would actually benefit from lower energy costs in the long run. I am not even convinced that this small increment will get passed on to the consumer. Developers charge what the market will bare. Increased costs from construction standards may not be passed on if the market will not bare the additional costs. It is the developer who might have to bear the costs. In the worst case scenario, we can as you pointed out have government policies in place to soften the blow and reset the cost burden of higher standards. Lastly on this point I would also add that Canadians who repaeatedly cite their concern for the environment and global warming should put their money where their mouth is and accept the cost of better built homes that use less energy.
As to your assertion that mandating won't do much. I disagree. You suggest that many developers do participate in such programs. I don't see too many LEED Certified/Bronze condos on the market. And I certainly haven't come across too many LEED certified low rise home builders. Have a look at the list of LEED for Homes builders:
http://www.canadagreenhomeguide.ca/providers.aspx
http://www.cagbc.org/leed_ap/directory.htm?keywords=&area_of_practice=12&province=ON&country=CA
None of our major developers from Ontario are listed on there. And if you have a look at board listings for the CaGBC there are several major developers again who are not participating. I think mandating their participation is necessary if they aren't going to do it voluntarily.
As for addressing the current home stock, I don't see how making someone get a sticker that says their 100 year old home is not super energy efficient will change much. It might change pricing a little and might add some efficiency as homeowners who do improve the efficiency of their home will finally benefit from their efforts. But as far drastically reducing emissions, that requires us to adopt much more stringent standards on all new construction not just homes. As far as I can see, the province is taking a pass on making that kind of real effort in favour of damaging home prices for existing homeowners while letting developers off the hook. I can't wait to see the reactions once this is rolled out and a lot of owners of older homes take a huge hit in home values based on the sticker on the side of their house.