Floor plan design city villa with basement improvement suggestion?

No one stays in the children's room. The basement (in modern terms UG) or the attic already provide a small apartment. The houses are big, there are hardly any rental apartments. What do you want to do then? Move away even though you don't want to? Turn your back on friends, work, etc., and follow the rental apartment? However, real construction usually happens in the mid-20s to early 30s. Either new or renovated and extended.

But behind hampshire there is, in my opinion, a better concept. If one of the children moves out, such a unit can easily be rented to a suitable tenant, and you still have your own space. Or one unit becomes accommodation for care staff, the other for guests, etc.

And that's what I meant, that maybe one should think about it again.

And, regarding how long the children will probably stay, hence the questions.

Just now has a suitable concept. It's not a big deal if the children are still there in 10 years.

That's why my question is whether the apartment is to be rented out or if it's just a byproduct. Housing Hampshire's concept on a small plot in a city villa is not so easy. Maybe he can help to move away from the mindset of bedroom, 2 children's rooms, bathroom.

What about later use of the children's rooms? There was a user who planned so that later the children's rooms can become a practice.

We were in Canada in a B&B that was planned so that the 3 children's rooms are used as guest rooms or, for example, at Christmas the children can use their old rooms again. Really cleverly done.

Just as a thought, the children are already relatively old and independent, so a children's area with 2 "normal" rooms (16-20m2), a small kitchen, and a small bathroom could also be an option. This could later be used as an apartment for one of the children or, if necessary, as a granny flat. Maybe a design for a multi-generational house would be suitable here? It is made difficult by the fact that you can probably get a cellar quite cheaply, but in the existing house dimensions the residential cellar is too small for both children and the technical rooms. For your use, it would probably make sense to reduce to only 2 floors, possibly raising the ground floor slightly to really have the basement at ground level on the 1.6m slope on the south side. The building envelope does allow for somewhat more house width and depth, possibly also a cellar garage. This way the children could have their own basement and the parents their own ground floor.

Usually, one calculates in the forum like this:

200sqm (your basement is actually living space) * 2000 = 400k
Ancillary construction costs 25k (set low because you can do underground construction yourselves)
Outdoor facilities 15k (not much either, since you also have EL)
Kitchen 15k
Miscellaneous, furniture, lamps, etc. 5k
Garage/carport 10-15k

Have you thought well about geothermal energy and solar system? Was the combination chosen out of conviction?

And at first glance, the cost breakdown is at least faulty in the following points:

Electrical (is a joke)
Tiling work + all the flooring work
Sanitary equipment (is that the 10k? for 3 bathrooms?)
Thermal and cold insulation work (what is that supposed to be, insulation of the whole house? with WDVS or what?)
You don’t have any doors? Not even front doors?

Regarding costs, I find flooring with parquet for

And at first glance, the cost breakdown is at least flawed in the following points:

Electrical (is a joke)
Tiling work + all the flooring work
Sanitary equipment (is that the 10k? for 3 bathrooms?)
Heat and cold insulation work (what is that supposed to be, insulation of the entire house? with ETICS or what?)
You have no doors? No front doors either?

Electrical could be right. The standard is only 4 sockets per room and one light switch. In the hallway, a toggle switch with a dimmer, etc. I think for this 1950s installation the price should fit, and that’s how the architect calculated.
Doors are probably locksmith work? No idea.

And what are parquet, wooden block laying works? That probably belongs more to the category of flooring work. But parquet for the big house for 1600€? If they're done at your place, I would also like to have a contact.