A house insulated to PassivHaus standards will drastically reduce the carbon footprint of space heating. Reducing your energy needs by 90% makes the origin of said energy largely irrelevant.
It's a given that all of our renewable infrastructure will have to be bootstrapped via our current system of non-renewable sources. So the fact that more efficient housing may do so too is not disqualifying.
The question is how much bootstrapping you need. Synthesizing liquid fuel from atmospheric gases and ocean water, for instance, requires only the bootstrapping necessary to build those facilities. Electrifying automobiles requires replacing all of the automobiles. Upgrading all housing to PassivHaus standards requires approximately enough construction to house over 7 billion people in new homes. Maybe half of that if you exclude people who don't already heat their homes, as well as the approximately tens-to-hundreds of thousands of Scandinavians whose homes already meet these standards.
I think you are suffering a little bit from analysis paralysis. I don't think anyone has a good answer on how much bootstrapping is needed. Even if we had a good estimate in mind, it's going to be wrong at some point. Even if we have a bad or no estimate, it is neccessary to move forward with an optimization method of following the derivative on actions that reduce carbon. It's not a closed form world, following promising trends is the best way to collect more information. And the world is a big place, we can trace multiple paths forward in parallel and continue to reduce carbon, as well as collect data to find more optimal paths.
I agree with that approach in principle. I don't think "let's immediately replace everyone's housing" is a good instance of that approach being followed rigorously.
I apologize if I've read too much into your comments, but I think you're the one making estimates replacing everyone's housing? It's certainly not something I'm suggesting.
I was replying to Tharkun's comment that upgrading housing to PassivHaus standards could "solve" the problem of generating energy for heating. It does no such thing unless you actually upgrade the housing, and there's a lot of housing in the world.
Depending on where you are and what your house is like, it could be feasible and financially viable to retrofit your house.
In other places (Japan comes to mind), houses have a relatively short shelf-life. Making passive the default could have a big impact there.
And in many urbanized areas, there is a housing shortage. This can lead to ridiculous price increases, or to a housing boom. Again, building new developments to passive standards could make a big dent.
I would love a magic wand to make every house passive, but I'm sadly aware that it's unlikely to happen. In many cases, the economics make sense.
