ᐅ 5.5 hours of discussion. Breathable or airtight?

Hi everyone,

We had a really exhausting day today.
We had two meetings at the prefabricated house center in Mannheim.
In the morning, we visited Keitel-Haus, and in the afternoon, Hanse Haus.

Our problem is: after meeting with Keitel-Haus, we thought we finally had clarity. But Hanse claims exactly the opposite.

At Keitel-Haus, this was our second long discussion, and this time we went into detail with a precise written quote and detailed descriptions of the individual building materials.

Now to the different statements, and we would appreciate your opinions as well.
You have the experience and are independent.

Exterior wall:
Keitel-Haus: vapor-permeable wall WITHOUT a vapor barrier (vapor retarder).
Including:
60mm (2.4 inches) wood fiber insulation board
200mm (7.9 inches) timber frame construction
200mm (7.9 inches) mineral fiber insulation
Wall thickness 29.2cm (11.5 inches)

Hanse: vapor-permeable wall WITH vapor retarder
Including:
150mm (5.9 inches) thermal insulation, thermal conductivity class 032
8mm (0.3 inches) OSB board
125mm (4.9 inches) timber frame construction (with mineral insulation)
8mm (0.3 inches) OSB board
vapor-permeable vapor retarder fleece
12.5mm (0.5 inches) gypsum board

So,
Keitel-Haus says: We build a proper vapor-permeable wall, so without any vapor retarders. This allows moisture to really escape outside, preventing mold growth.
Hanse says: That’s nonsense, there are no houses that can "breathe". We have a vapor retarder because we want to hold back water vapor, i.e., moisture. We don’t want it to enter the wall, as it would cause damage. Without a barrier, mold would eventually develop.

What is correct here?

Topic 2
Heating technology / ventilation:

Keitel-Haus:
They considered our wishes and said that while they think controlled residential ventilation is good, they do not recommend controlled ventilation with heat recovery. I don’t remember exactly why, but there was a lengthy explanation. Anyway, probably because of underfloor heating, we wanted a heat pump.

Hanse:
They tried to persuade us to get a different kind of heat pump and insisted it would be better to have controlled ventilation WITH heat recovery.
It would save energy, and windows can still be opened (which we want, especially at night while sleeping and sometimes in summer).

If I remember correctly, I recently read only negative things about that kind of heat pump, and that it would financially disadvantage us.
Hanse says: Nonsense. If the house is built properly and the system is installed correctly, this kind of heat pump is best, and they can ensure it is the most cost-effective.

Topic 3
KfW 40/55 standards

Keitel-Haus:
KfW 55 is optimal and can be achieved without problems according to our requirements (photovoltaics, underfloor heating, heat pump, vapor-permeable wall).
KfW 40 requires too much effort and is much too expensive. The savings wouldn’t justify it.

Hanse:
KfW 40 or better yet Passive House, since from 2020 Passive House standard is mandatory anyway.
The difference from KfW 55 to KfW 40 would only be about €9000 and corresponds to additional insulation under the slab and roof. No extra technology would be needed, and the savings would be enormous!
Their walls already meet KfW 40 as standard.

Topic 4:
Exterior wall insulation

Keitel-Haus builds with wood fiber insulation board. Styrofoam (EPS) is standard but not recommended because it is vapor-tight. That’s why they offer a better "open" wall.
I know Styrofoam is extremely poor in fire performance. I don’t like it at all.

Hanse:
I had no clear answer; I couldn’t really get details. They just said Styrofoam is not so bad, and their thermal insulation contains some graphite.
It seemed to me like Styrofoam with graphite additives or something similar.

I know, lots of questions again.
I have already spent many hours reading but still don’t feel much wiser.
These topics are very complex and sometimes a bit beyond me.

From the feeling we have, we would build with Keitel-Haus.
The Hanse representative was arrogant and "aggressive." I even almost argued with him because he was unwilling to discuss most points, including providing a written offer. He said he only bothers if he knows you really want to build with them. For me, a comparison makes no sense without different offers and service descriptions to compare.

We also looked at Fingerhut, but after 6 weeks they still haven’t provided an offer. So that’s a no-go for us. The "salesperson" seems to prefer working his side job (entertainer).
Rensch-Haus gave us many verbal promises that everything would be possible (of course, for extra money, everything is possible), but 90% of what should have been standard was not in the service description.