A above-ground living basement?

He wants to save money, bet? Some kind of prefab building with a pitched roof.

Of course, I always like to save money. But the origin of the idea is my amateur assumption that concrete is more stable than bricks or aerated concrete (meaning I would have thinner walls with concrete) and that this would be an alternative to timber frame + external ETICS.

"Prefab building with pitched roof" describes it quite well. The basement manufacturers do advertise with concrete slabs as a sandwich with insulation in between.

The origin of the idea, however, is my amateur assumption that concrete is more stable than bricks or aerated concrete (which means I would have thinner walls with concrete) and that I would thereby have an alternative to timber frame + external ETICS.

Oh, I see. So your question basically is: "assuming I have a wrong assumption, do I then arrive at the right result?", and the answer is simply: "no.".

Whether 16 cm of structural solid wood (plus drywall, chipboard etc. on both sides) or 17.5 cm of butter biscuit: both will be built onto you with 16 cm of hazardous waste boards glued on.

The basement manufacturers advertise concrete slabs as a sandwich with insulation inside.

Other than as lost formwork, you simply can't (affordably) transport that stuff. It is also more used in multi-storey residential construction where time is money.

The idea that the insulation in between could save overall thickness would also be amateurish: instead of 33.5 cm, I would rather see your wall overall at 44 cm.

I still don’t fully understand

you want to build with concrete, but it must not be visible
an additional full floor was not your intention
saving money was not your intention (especially since it was already suspected that it is even more expensive)

but you believe that concrete is more stable than a masonry house?
what are you afraid of? tsunami? landslide? nuclear bomb?

or is it about the walls being thinner? what advantage does it have if the wall is 30cm less thick?
on the other hand, because concrete has rather poor insulating properties, you need more insulation for it. A masonry wall with perforated bricks requires less thick insulation.

if you absolutely want ETICS, that is also possible with masonry walls
personally, I don’t consider ETICS an advantage either (in my opinion flammable, hazardous waste, not so durable).

why do you already exclude masonry houses or want to avoid masonry works? I still consider that the best option.

maybe you can try to specifically point out again which advantages you see in the concrete variant and why timber frame or masonry walls should not have these advantages as well

I do not want to exclude masonry walls at all. On the contrary, I would prefer masonry without external insulation.

but: the wall becomes very thick if it has to insulate well. Also, the new self-insulating materials seem very crumbly to me, if I may put it layman-like. And they must be carefully installed (glued!) by professionals if the insulating properties are to be really good.

My partner would rather avoid an external ETICS.

that is why it seemed like a good idea to me when the basement providers say that they place the insulation as an intermediate layer between two concrete slabs. Stable. And not too thick.

Whether 16 cm solid structural timber (plus plasterboard, chipboard etc. on both sides) or 17.5 cm butter biscuit: both are built onto you with 16 cm hazardous waste panels glued on.

I do not understand the answer. There is a wide spectrum in timber frame construction and solid wood construction. The "healthy living" construction method, without ETICS, without foils etc., but diffusion-open, is modern. Is the above statement meant to apply universally to all buildings also made of wood???

I do not understand the answer.

It was about a fundamental misconception of the OP, as is also made clear again in

My partner would prefer to avoid an external ETICS. therefore it seemed like a good idea to me if the basement providers say that they put the insulation as an intermediate layer between two concrete slabs. Stable. And not too thick.

Therefore, I wanted to clarify that when building with ETICS, the question of whether there is stone or timber frame behind it only makes a difference in the total wall thickness "after the decimal point." And actually, I hoped it would be clear / become clear that it does not matter for the insulation effect (or total wall thickness) whether the insulation is outside or in-between. However, as you can see, it seems the OP still has not understood this:

On the contrary, I would prefer masonry without external insulation. but: this makes the wall very thick if it has to insulate well.

I will summarize once again: 1) In the concept of "building material shell plus insulation shell" it makes no noticeable fundamental difference whether the building material shell consists of stone or timber frame construction. Most providers offer a total wall thickness in the range of about 29.5 to 33.5 cm. 2) In monolithic aerated concrete, 36.5 cm is sufficient. 3) Whether the insulation is positioned outside or in-between does not matter for the total wall thickness. Concrete with insulation comes to about 44 cm in total (Energy Saving Ordinance), at this thickness you already reach KfW40 in timber frame construction.