[fulafel]

Have a look in eg p.43-46, 75, 117, 143 in https://portal.research.lu.se/en/publications/passive-houses... for one case of building standards back in 2009. There isn't really a energy efficiency limit there being approached, just a matter of what had been picked as a cost efficient target, so there are no absolutes. I'm betting current designs are more efficient, as that has been a constant trend, but don't have newer references on hand.

In practice it seems going much lower than half as much as hot water uses may be wasteful investment as long as water is not heated with local renewables.

[trashtester]

The savings depend on what you benchmark against. But energy savings between 50-75% for a new house compared to an old one, seems realistic. And maybe older houses could be modernized in ways that would save 25%-50% in many cases.

Tearing down all old houses and building new ones is obviously not an alternative, so a transition to new standards is likely to take 50 years or more, even though some of the benefit can be realized by modernizing existing housing.

But even $30000-€50000 euros to lower energy consumption is also a big investment for many families, and even WITH that investment, heating prices in Norway and Sweden will be 2-3x historic prices if prices stabilize at current levels, especially if the governments stop subsidies.

I think every country will have trouble bringing their population to accept having to use electricity at prices about €0.1/kwh, even if over a very long term, it is possible to build houses (at extra costs) that bring the consumption down a bit. At such prices, people in Germany, Denmark, Poland, Hungary etc will simply continue burning natural gas indefinitely.