160m2 detached house in timber frame construction on the north slope with basement

Just quickly converting the attic into 2 children's rooms with a loan hanging over your head – it's not impossible, but I would be careful. It surely won't cost less in 5 years than it does now, and the loan probably won't be paid off by then. So where should the money suddenly come from?

Right,
That is not an option for us.
By the way, there is a small street on the north side and behind it a wooded area, so the view is really quite good.

The subsequent conversion of cold roofs is not trivial, so it is better to include the attic space in the building envelope right from the start and also have all media installed.

Just quickly converting the roof into 2 children's rooms with a loan hanging over your head - it's not impossible, but I would be cautious. It certainly won't cost less in 5 years than it does now, and the loan will probably not be paid off by then. So where should the money suddenly come from?

The lines are already being laid... it's about the interior finishing, which can be postponed if it's not even clear whether there will be children in the house. If money is tight, you don't have to build something that will never be needed. Pre-installing the installations is not much more expensive. The interior finishing can also be done in stages. TE won't be the first to have to make sacrifices or do some work themselves.

By the way, there is a small street on the north side

Oh... that's why the rooms for feeling good won't get any better.

The subsequent conversion of cold roofs is not trivial, so it's better to include the attic space in the building envelope right away and also install all utilities then.

Who is talking about a cold roof? Something like that should be planned beforehand. If a conversion is very likely to be planned, then the attic space is built as a warm roof. See above for more.

But I really don't care: you can also nicely plan the garage below and have the three-year-old sleep next door I'm out with such a plan.

But I’m actually supposed to not care: you can also nicely plan the garage downstairs, and let the three-year-old sleep next to it I’m out with such planning.

I don’t see it as that dramatic at all. The garage was already discussed as being outside the house. The children’s rooms then just go on the other side.

My niece just converted the attic. 50,000 – but a cold roof. Whether I have half of it converted sooner or later, the total cost ultimately remains about the same, right?

Doing it yourself with a job and a child – that’s definitely a challenge. The man earns the money – the woman takes care of the kid full-time. Only night shifts and weekend work left. Well, maybe young people still manage that. I barely manage to wash my own laundry on the weekend without a child.

But it’s true, the house on the plot would be much better off with a basement. I would paint the garage first instead of the basement. Of course, the question is how much that saves.

The garage has already been discussed to be removed from the house. The children's rooms will then just be on the other side.

I don't understand.

The original idea from the OP was to remove the garage, making the total floor area a bit smaller, then put 2 children's rooms in the basement (which only allows windows facing north and a bit east/west ... so a carport would have to go somewhere). Then on the ground floor, as before, cooking/eating/living/working, and in an attic with a smaller knee wall, a pure parents' area.

To the objection that these wouldn't be nice rooms (dark), the OP answered that there are no children yet and one wouldn't know if maybe for some reasons having children wouldn't work out either. Hence Yvonne's objection to put the parents' area in the basement, cooking/eating/living/working on the ground floor, and the attic as a warm floor just prepared in case it works out with the children.

I understood it to mean that the money is only enough for 2 floors - whatever kind they may be. And that won't change in 5 or 10 years - with or without personal contribution.