It's lighting, definitely. If anyone still has T12s, change that out, or use incandescents. Lighting would probably be less than a two-year payback. Controls would be a very quick payback, two or three years. If there's an older boiler or chiller, that would be a medium length of time for payback.
Where the big jump comes in—and it differs for different buildings—is when you start looking at the envelope. You'll start looking at the walls and the windows. That's expensive. In order to get to the 40%, you're probably starting to look at the envelope. You're probably also starting to look at on-site generation, either with gas or with renewables of some sort. Certainly when people talk about zero carbon, you're definitely making major investments in on-site generation.
To take an existing building to zero carbon is.... People are just getting there with new buildings. You'd be looking at reskinning. Again, in Europe, where the energy prices are much higher, we see examples of that. People are just starting to look at that now in Canada, but the pricing is still difficult.