Additional insulation in the Bien-Zenker prefabricated house – What makes sense?

Dear forum,

we are facing some decisions regarding our planned prefabricated house project with the company Bien-Zenker.

First of all, it is about the decision on insulation.

By default, Bien-Zenker has a Kfw-40 exterior wall + KfW-40 windows, the rest is standard, i.e. labeled as an energy-saving house by them.
We are therefore considering additional insulation under the floor slab, as this can no longer be done later, plus insulation of the front side of the floor slab.
Furthermore, the company offers additional insulation of the upper floor ceiling to the unconverted attic. To bring the house completely up to KfW-40, the roof would then still have to be insulated?

What insulation do you recommend and which are the most efficient?
For example, does insulation of the roof actually bring any benefit (in winter as well as in summer) if the ceiling to the attic is already insulated?

Thank you very much!

Which insulation do you recommend and which are the most efficient?

Standard. The rest costs money and brings very little benefit. You can insulate the top floor ceiling yourself later for 1,000€ if you want.

Insulation of the top floor ceiling can be done by yourself – we did that too.

Insulation under the floor slab and on the sides of the floor slab we had done. Exactly for your reason, because it is no longer possible later.

As says, I don’t know if it helps much and I also think you never recover the costs through energy savings. Nevertheless, it felt better for us to do it.

Dear forum, we are facing some decisions regarding our planned prefabricated house project with the company . First of all, it is about the decision on insulation.

Dear Al-Emm, there is no need for you to start a separate thread for every aspect of a Bien-Zenker house. Just bundle all questions about your house project in a single thread, after all, it is only ONE project. Just one cross per person, like in Life of Brian, that's enough.