Mineral insulation vs. wood fiber insulation prefab house

Hello dear forum,
we planned a prefabricated house with the company Weiss and are currently facing the question of which wall structure we should choose.

The Klimawand or the Klimawand Natur.
They differ in that between the wooden frame construction, a mineral insulation material is used in one case and in the second case a wood fiber softboard.

What advantages and disadvantages would you see?
Healthy living is important to us.
The Klimawand Natur costs €12 per m² extra.

Best regards

Mineral fiber burns less readily, but wood fiber also chars off fairly controlled. Wood fiber offers better sound insulation and better summer heat protection. Mineral wool requires a lot of energy in production, wood fiber uses renewable raw materials and requires less energy in manufacturing. Wood fiber is considerably more expensive.

The living comfort or the "healthy living" you mentioned is identical for both materials (except for minor details as mentioned above). You absolutely won’t notice any difference. You could also insulate with EPS or build monolithically. It’s all the same. At least when you live inside.

The essential difference is already contained in the name. Although the wood fiber insulation boards are not really "natural," the majority of the material is of natural origin. However, they are mixed with fire retardants. This leads to lower energy consumption during the production of the insulation material. Mineral fibers require high temperatures and sometimes high pressure, resulting in a worse ecological balance. The difference in construction will have no impact on your life in the house.

Sound insulation is also given with the classic construction; points of approach are rather windows and connection points.

What is relevant: In both cases, you have 12cm of wood fiber on the outside. Compared to EPS, which could be used alternatively, it has good sound insulation and a high heat storage capacity. This moderates temperature differences in the exterior plaster in winter and summer. This leads to less cracking in the long term and especially less algae growth. The latter tends to occur after 5 or more years, once the "plant protection agents" (which are not allowed to be applied on any field in Europe - but may be undeclared in plaster) have been washed out by rain.

Healthy living is important to us.
The Klimawand Natur costs an additional €12 per m².

Per square meter of living or wall surface?
Free yourself from the romantic notion of "breathing" walls in the sense that your family would inhale their breathing air through the exterior wall like through a Covid protective mask. No air at all passes through the wall! – the “climate” only passes indirectly / figuratively through the wall, i.e., in the way the wall cooperates with the thermal conditions in the heat transfer process. For the insulation material – which in any case is not spun by bio-silkworms in either case – the further wall structure does not behave like a tea bag, but like a castor container. The insulating effect could therefore safely be achieved even with recycled paper from Express and Bild newspapers, without the residents becoming stupid from it. Also, gas passage from binders is not to be expected through a gypsum board.

The relevant difference here corresponds more to the U-values of the respective wall constructions: this indicates the duration of the heat difference passing between inside and outside, and thus also the phase shift of the outside air temperature fluctuations. That it “stinks” of mineral fibers or “smells” of freshly sawn logs inside will make no difference for human noses or measuring probes. None of that would pass through!

As an “old 68er,” I am always amazed how much Venceremos still sticks in the minds of young builders today after more than forty years in the slogan “jute instead of plastic.” Whether that should make me more happy or scared, I am still undecided.

So the insulation effect could also be safely achieved with waste paper from Express and Bild newspapers, without the residents becoming stupid because of it.

That doesn't sound nearly as good as when you say "cellulose insulation"

As an "old 68er," I am always amazed at how much Venceremos is still behind the slogan "jute instead of plastic" in the minds of young builders even after more than forty years. Only whether I should be more pleased or frightened by this, I am still undecided.

Somehow the different house builders have to differentiate themselves. Here, the topic of healthy living alongside environmental protection is a welcome vehicle. Whether it’s really better in the end or just apparently so is not even relevant.

Although, given the price difference compared to the wood fiber variant, I would tend toward that. Surely you can spend €2500 more senselessly on house construction, and even if the interior insulation no longer contributes much to heat protection, it won't hurt. I also find it more consistent overall to rely on wood fiber in both insulation layers rather than half and half.

I also find it more consistent overall to use wood fiber in both insulation layers instead of half and half.

At least within a sandwich, as much monolithicity as possible is good, in my opinion. Any nesting of different thermal conductivities is a complication whose risk potential is hardly researched. And this even applies to the same material but with a different density.