Same price: Kfw55 with Poroton monol. OR Kfw40 with Poroton WDVS?

Sometimes I really believe that if we were the generation of our (great) grandparents... then Germany would no longer exist. What nonsense we are talking about here nowadays.

Spending tens of thousands of euros more because the neighbor throws a party twice a year, which he has to reduce to quiet-room level by 10 p.m. anyway...
And one forum further, people are whining about house prices that no one can afford anymore.

Whole wardrobes are built in the hallway for jackets and hats, pantries are constructed for the canned goods bought at Aldi (which you can buy there every day except Sundays and public holidays)...

Sometimes I think a little recession would do us good... to bring some people back down to earth.

What does this have to do with choosing the stone?

At the time, filling it would have cost us 6000 euros more. But we had no idea about all that back then.
I still wonder why the experts keep recommending this stone. It doesn’t make sense to me.

And I’m not talking about a party once a year here. It’s a new development area. There is always building and doing, everyone has at least 2 kids, lawns are mowed, etc., there is always something going on. I would very much prefer not to experience all that 1:1 inside.
The 6000 euros would have been worth it to me. I would have also been okay if someone had told me: I’m warning you—the stone is such and such, and if you want it better, it costs 6000 euros. But the statement was: no need at all. 30 km/h zone in the countryside. It’s great. And not only from one house builder. We were with several.

I think the OP has his answer now. And can act accordingly.

That I like to have supplies in the house, just like my grandparents used to because Aldi might not be open every day from seven to 8 pm in times of crisis, is irrelevant.

Sometimes I think a little recession would do us good... to bring some people back down to earth.

Of course, there are also "downsides" when the grandpas and grandmas can no longer tell today's kids about the hardships - but only downsides in quotation marks. Incidentally, this year we are practically celebrating the anniversary "100 years since the inflation peak" - and when I look at what all cost 20% less at the mentioned Aldi a year ago, I can understand the hoarders *LOL*

With the monolithic one, the base plate would also be 12cm larger all around, right? Since with the thinner stone, the insulation is not applied there? For a 10m * 10m * house, that would amount to 12m2 of area which at least does not count towards the built-up space, right? (10m*10m*0.12m)

In the monolithic version, the base slab would also be 12cm larger all around, right? Because with the thinner stone, the insulation does not go on it? For a 10m * 10m house, that would amount to 12m2 of area which at least does not count as usable space, right? (10m*10m*0.12m)

I do not follow the naive calculation (not only because of the included slip error). Mathematically, you would need to know to which fraction you belong in this regard: some consider the wall thickness as a whole, in their eyes the wall begins regardless of material at the room/wall boundary; others see it similarly but from the boundary WDVS/plaster (I, as an experienced planner, belong to the third fraction and think of the wall following the layout grid with the master edge at the transition stone/insulation). By the way, the latter is the mother of the porcelain box called "avoidance of botched work pockets". I would plan a base slab, as well as a strip foundation, always projecting beyond the load-bearing wall shell on both sides (and in the case of a facing shell, added with its total projection). Insulation thus partially "overhangs". Where exactly the outer edge of the base slab runs has, as explained above, a lot to do with how the planner thinks.

With the monolithic approach, the base slab would also be 12cm larger all around, right? Because with the thinner stone, the insulation doesn't go on it? That would make 12m² of area for a 10m * 10m house which at least doesn’t count as built space, right? (10m*10m*0.12m)

Depends. There is the option to set the first row of stones with narrower stones, then insulation goes in front of these and the base slab. From the second row on, the normal stones are used.