5.5 hours of conversation. Diffusion open or closed?

Hi @ all.

We had a really exhausting day today.
We had 2 meetings at the prefabricated house center Mannheim today.
In the morning we were at Keitel-Haus and in the afternoon at Hanse Haus.

Our problem is, after Keitel-Haus we thought we finally understood more. But Hanse claims exactly the opposite.

At Keitel-Haus today it was our 2nd long conversation, today it went into detail, with a precise written offer and detailed descriptions of the individual building materials.

Now to the different statements with the request that you also give your opinions on this.
You have the experience and are independent.

Exterior wall:
Keitel-Haus: diffusion-open wall WITHOUT vapor barrier (vapor retarder).
among others
60mm wood fiber insulation board
200mm wooden frame construction
200mm mineral fiber insulation
Wall thickness 29.2cm

Hanse: diffusion-open wall WITH vapor retarder
among others
150mm thermal insulation, thermal conductivity group 032
8mm OSB board
125mm wooden frame construction (with mineral insulation)
8mm OSB board
diffusion-open vapor retarder fleece
12.5mm gypsum board

So,
Keitel-Haus says: We build properly diffusion-open, so without any vapor retarders. This way the moisture can really be guided outside and no mold forms.
Hanse says: Such nonsense, there are no houses that can breathe. We have a vapor retarder in place because we want to hold back the water vapor, i.e. moisture. We don’t want it to get into the wall because it wouldn’t be good for it. Without a barrier there would eventually be mold.

So, what is right?

Topic No. 2
Heating technology/Ventilation:

Keitel-Haus:
Took our wishes seriously and also said that although he considers controlled residential ventilation good, he does not favor controlled residential ventilation with heat recovery. He finds that not so good. I don’t remember exactly why, but he explained it at length. In any case, we probably wanted, because of underfloor heating, an L.W.W pump.

Hanse:
Tried to persuade us to an L.L.W pump and also that it would be much better to have controlled residential ventilation with heat recovery.
It would be more energy-saving and you can still open windows (which we want, especially at night when sleeping and partly nice in summer).

If I remember correctly, I read only negative things about the L.L.W pump the day before yesterday and that it would cause a financial loss.
Hanse says: Nonsense, if the house is built properly and the system is installed correctly etc. the LLW pump is the best and they will make sure it works out best for me.

Topic No. 3
KFW 40/55

Keitel-Haus:
KFW 55 optimal and feasible without problems with our ideas (photovoltaics, underfloor heating, LWW pump, diffusion-open wall)
KFW 40, way too much effort, way too expensive. You wouldn’t get much more savings.

Hanse:
KFW 40 or better passive, since from 2020 passive would be mandatory anyway.
The difference from KfW 55 to KfW 40 would only be €9000 and would only mean extra insulation under the floor slab and on the roof. No further technology would be needed. And the savings would be enormous!
Their walls are standard already KFW40 anyway.

Topic 4:
Exterior wall insulation.

Keitel-Haus builds with wood fiber insulation board. Standard would actually be styrofoam, but he doesn’t recommend it either, also because it is diffusion-closed. That’s why the better “open” wall.
Styrofoam I know… extremely poor fire behavior. I don’t like that at all.

Hanse: No idea, I couldn’t really squeeze out what it actually is. He just said styrofoam isn’t so bad and their thermal insulation is something with graphite.
It seemed to me that it’s styrofoam, only filled or something with graphite.

I know, many questions again.
I have already spent many hours reading, but still don’t get much wiser.
The topics are so complex, it’s partly a bit too much for me.

From the feeling, we would build with Keitel-Haus.
The Hanse guy was so arrogant and “aggressive,” I almost argued with him sometimes because he hardly wanted to accommodate anything, also regarding a written offer. Only if he knows you really want to build with them does he put in the effort. And a comparison by me is useless if I get different offers and compare the construction services.

We also had Fingerhut, after 6 weeks still no offer. So they can forget us. The “salesman” apparently prefers his side job (entertainer).
Rensch-Haus had promised us a lot orally and that everything would go and be feasible (surely for money, anything is possible) but 90% of what would normally be standard did not match the description of construction services.

Now a vapor retarder (not a vapor barrier, those are two different things) must be used if you don't want your wall to eventually rot away (however, you can also build without it but then there is no error tolerance and you don't really believe that everything will be flawless during construction).

Breathable houses/walls do not exist, this is a marketing gimmick or as real as Santa Claus.

A controlled residential ventilation system without heat recovery is no longer state of the art (still better than none at all) but nowadays I would only buy one with heat recovery and an enthalpy exchanger.

An air-to-air heat pump is great in Spain... in Germany it's basically a money-wasting machine even though some will argue otherwise... everyone knows that a "normal" air conditioner in the house is more of a luxury and has high acquisition and operating costs. Now an air-to-air heat pump is an air conditioner that just produces heat.

So if you want a heat pump for the house, then at least an air-to-water heat pump.

You have concerns about the polystyrene and fire behavior??? But you want to build a wooden house??????

Exterior wall:
Keitel house: diffusion-open wall WITHOUT vapor barrier (vapor retarder).
Among other things
60mm wood fiber insulation board
200mm timber frame construction
200mm mineral fiber insulation
Wall thickness 29.2cm

We basically have the wall structure you described (but hemp instead of mineral wool) and we have a vaporretarder (between OSB and gypsum board).

Vapor retarder or vapor barrier? We also visited Keitel-Haus and would have built with them. All the others were such quacks! Keitel-Haus has building biologists on board who have studied this....they really know their stuff and thanks to our civil engineers in the family I know they weren’t talking nonsense. However, if anything, I recommend hemp insulation. It can transport moisture much better due to the fiber structure. In the end, we didn’t build with Keitel-Haus because they were more expensive than the builder with monolithic brick wall construction. So it will be a solid house for us. Keitel-Haus is still likeable to me though.

Everyone else are quacks, very professional attitude. And because you hired a [Baubiologen], you are targeting that. Then I can become self-employed as a house builder myself. Sorry, but those are arguments that only make me shake my head. There are many good house building companies, as well as solid house builders.

Not fully rested yet or why are you being so snippy right away? Everyone else we dealt with were quacks from our perspective!! We always had experts present at the discussions. Of course, there are many good companies on the market...? Did I question that? It’s just that none of them were included in our ranking.