Avg. gas consumption of 12000kWh per year for a house
Funnily enough - this seems to be a rough ballpark figure of heating energy spent
anywhere. Houses in colder climates are just insulated better, because there is natural motivation to do so.
My house uses around 15MWh per year, and it's built in 1952 and energy renovated in 1982. Original insulation is sawdust + wood chip mix, 100mm in walls, and 300mm in ceiling and floor, plus walls have some wood fiber board for some extra insulation. In 1982, 50mm of mineral wool was added to outside walls.
Modern houses per current regulations use like 300mm of modern-day mineral wool in the walls, and 500mm or even 600mm in the attic. We have finally realized how important airtightness is, so newly build houses are actually pressure tested to prove absence of air leaks. As a result, modern houses consume very little heating energy, even given the cold climate. But we still see the magical number ~15MWh/year around, though, because people just build larger and larger houses, and as a result, are more and more in debt!
It seems to be some kind of magical constant, people can psychologically afford spending 10-25MWh/year for heating so that is what they do. If they live in warmer climate, they insulate very poorly, and get to that number. If they live in colder climate, they insulate better, only to get to the same number. If they want a bigger house, they will insulate even better.
What needs to change is the absolute value of this number, because energy is more expensive, a limited resource we have overused for decades. One way is to use heatpumps, for example, my 15MWh of heat comes from approx. 6MWh of electricity because of the heatpump. Another option is better insulation. And obviously - both.
Also the fact people used to live in 100m^2 houses with large families (say 4-5 kids), and now you suddenly need 250m^2 for no kids or 1-2 kids.
Combine all this knowledge and try to see if you could live in a 100m^2 house again, insulate it better, and use heatpump, and that 15MWh is down to 3-4MWh. A totally massive drop.