With top quality insulation, the orientation of the house, trees and vegetation and all the rest, I’m sure that could be the case….but is not the norm.
Also, heating one level is cheaper than two.
Houses with a downstairs bedroom or a space that can be converted into a downstairs bedroom will always be more desirable.
Don’t get me wrong, we sleep upstairs….the kids have the downstairs bedrooms.
Not necessarily if house is built round a central point as heat rises. Our gîte is 3 story with a poêle centrally on ground floor, and open staircases. The top floor is toasty! More so than ground floor as we still have area downstairs that needs external insulation.
Passive houses are rarely single story.
Houses will differ enormously… but I do agree that having downstairs facilities (bed/toilet etc) will always come in handy.
The gendarmes are one thing, especially the GIGN, but it’s the CRS you might need to worry about more.