300k budget for a 130 sqm single-family house?

To implement it is certainly possible, the plot would allow it.
Can I manage with about €300/sqm for the basement? Then the extended garage would probably be cheaper again.

Where do you get €300 per sqm from?
I estimate that €600 is more realistic and very expensive earthworks including landfill fees.
That means a basement of that size will certainly cost €50k. That’s also why there’s the idea of additional living space instead of a basement. It also depends on the plot; if it is on a slope, a basement can make sense.

I read the 300 € in various forums, probably a bit too optimistic. 50k is already a big number! The plot is slightly on a slope, yes.

For us, it is such that we can drive into the garage at street level and at the back of the house on the "EG" have direct access to the terrace. Here, a basement obviously made sense, especially since there is still a nice room with a normal window on the street side that can be used as an office/GZ. If the terrain is not so steep, you just have to think about it. After the increasingly extreme weather conditions, however, I would not build below street level, meaning driving downhill into the garage/basement...

Do you have €280,000 for 125 sqm (with the mentioned extras?) including incidental construction costs?

that's right. we paid a total of €340,000 for the house – €63,000 net land costs (without notary, etc.). that makes just under €280,000 for the house including incidental costs and all the mentioned extras. for €80,000 apart from the incidental costs there are already some nice extras included. we basically took everything you can add as fun extras. no trade went to standard :)

125 sqm is not a big house, correct. but it can be sufficient for 4 people, including an office on the ground floor. a children's room with 15-17 sqm is not "barely acceptable." do they all probably come from wealthy families?! as a child, I had an 8 sqm room without heating, later 12 sqm with heating (at 16 years old). I think 15 sqm is quite decent. of course, it can gladly be 20 sqm or more, but that has to be paid for as well. you can fit a bedroom of almost 14 sqm perfectly (3-meter wardrobe, 2x2 meter bed and 70-80 cm circulation space on each side of the bed (except the head side)); more would basically be a waste since you only use it for sleeping. or you use the room for other things (office/retreat room).

instead of many expensive extras, you can of course also easily build 30 sqm more. electrical shutters out, fireplace out, ventilation system out and suddenly 20-30 sqm more space is possible.

that's right. we spent a total of €340,000 on the house - €63,000 net land costs (excluding notary etc.). that makes just under €280,000 for the house including incidental costs and all the mentioned extras. for €80,000 you already get some nice extras in addition to the incidental costs. we actually took everything you can fit in as fun stuff. no trade went to standard :)

125sqm is not a big house, right. but it can be sufficient for 4 people, including an office on the ground floor. a children's room with 15-17sqm is "not just barely acceptable". do they all probably come from rich families?! as a child, I had an 8sqm room without heating, later 12sqm with heating (at 16 years old). I think 15sqm is already quite decent. sure it can be 20sqm or more if you want, but that also has to be paid for. you can fit a bedroom very well in just under 14 sqm (3-meter wardrobe, 2x2 meter bed and 70-80cm clearance on each side of the bed (except the head side), more would basically be a waste, since you only use this for sleeping. or you use the room for other things as well (office/retreat room).

instead of many expensive extras, you can of course also easily build 30sqm more. electric shutters out, fireplace out, ventilation system and suddenly 20-30sqm more space is possible.

Were you happy in your 8sqm room? I also had a similarly small children’s room at times and hated it because everything was full and you could hardly move. Just because you didn't have it better yourself doesn't mean you can’t try to make it nicer for your children. Our children’s room is the biggest in the attic...

the one thing you want, the other thing what you can do. 15sqm are certainly not a small storage hole or child torment as a children's room. I found the 8sqm sufficient because I was always outside anyway. a (loft) bed fit in, a desk, a stereo furniture, various cupboards under the bed, and a wardrobe. and you could walk properly in between. I would no longer expect that from my children today, but the youth welfare office would even put them in 7sqm. we want to take in foster children, he said, my almost 7sqm office on the ground floor could also be used as a children's room so that we could take in 3. I politely declined first :) that is MY room ^^ my darling *g