Basement planning prefab house - outsource? What to consider?

Good day,

I am currently planning a construction project for a city villa with KFW40+ and approximately 140m² + basement.

The basement is a topic that I have not wanted to deal with until now, but it is definitely necessary and, in my opinion, one of the most important things here. I also think that quite a bit of money can be saved here if this matter is approached correctly.

For my plot, I need a waterproof basement with a white tank for pressing water... In other words, the most expensive and complex thing a basement requires.

At the moment, I have also been offered everything including the basement by my prefabricated house suppliers. But of course, I have no idea how expensive a basement might be with a civil engineering company, apart from the prefabricated house supplier. Is this even an option? Should one look in this direction, or rather have everything done from one source? Is it possible to save money here at all? According to the prefabricated house suppliers, there are hardly any price differences here (of course, they also want their commission). However, I think that one can save a considerable amount here (especially with such a basement).

Have you had any experience with prefabricated houses and basements? How did you approach the whole thing? What do I need to pay attention to when building a basement? I am grateful for any help!

We are currently already very far along in the house planning and also already very detailed in the offers, but the basement is still a topic that I have not yet really dared to approach. Perhaps unjustly?

I look forward to your help!

Best regards

Simon

Have you had any experience here with prefab houses and basements?

As much as I have gathered from this forum, prefab house builders usually have their own fixed basement builder, such as Glatthaar. They don't rely on others at all. As a homeowner, you then really don't have any choice.

KfW40+ and an external basement... phew. A hot number for everyone involved! I would rather do without one of these two features.

Yes, that's clear. But theoretically, I can say: Please just deliver the house. I will provide the basement + floor slab myself.

Some [Fertighausanbieter] have no problem with that, others, however, do...

KfW40+ and an external basement... phew. A hot topic for everyone involved! I would better refrain from one of these two features.

That's exactly what I thought too. How does it all work? Who accepts it from me and certifies the KfW40+? If everything is handled by one provider, it is definitely easier, of course.

That's why my question is to what extent something like this is even possible and whether you can or should save money here at all?

(Wood frame panel) prefabricated houses were previously often placed "from OKKD" on site-built basements – and in the case of unproblematic soils, home builders also gladly saw this as an opportunity for own work. From my point of view, it was a great blessing for quality assurance that many prefabricated house manufacturers more than thirty years ago began to establish their own basement construction subsidiaries or – which currently dominates – to form alliances with specialized (prefabricated) basement builders. I would never come up with the idea to buy only the body and interior from Opel and the engine and transmission from Ford. Forget the idea of this promenade mixture. A prefabricated house manufacturer who does not – with satisfied customers! – recommend certain basement builders would be out of the running for me.