24 cm Ytong + insulation or 36.5 cm Ytong

: Hehe, you misunderstood me - I did not want to invite a religious war

For me, Ytong is the worst... poor sound insulation

Sound bridges are more likely caused by construction errors than by the choice of building materials. Light does not necessarily mean good damping, because even something light can be stiff...

and thermal bridge issues

... the fundamental "thermal bridge" of a single-layer structure is also not a privilege of any particular building material. Aerated concrete as well as expanded clay combine the stability of solid building materials with long paths for all waves around the cavities in the structure...

Plus unnecessarily thick walls with reasonable thermal insulation.

... many of the fashionable wall constructions with insulation panels have an overall thickness of more than 40 cm, a 36.5 cm aerated concrete wall is comparable.

: Hehe, you misunderstood me - I did not want to invite a religious war

Ok, let's say you understood correctly, and still replied

Sound bridges are more likely caused by design errors than by the choice of building materials. Lightweight is not necessarily good at damping, because lightweight can also be stiff ...

True. But you can’t draw any conclusions with that argument. Without design errors, a Ytong wall has one of the worst sound insulation values of all possible wall structures.

However, I think we agree here: Much more important than the actual wall structure is that the company knows the wall structure well and builds properly.

... the principal "thermal bridge" of single-layer construction is also not a privilege of a certain building material. Aerated concrete as well as expanded clay combine the stability of massive building materials with long pathways for all waves around the cavities in the structure ...

I was only referring to the comparison of ETICS wall vs. monolithic. Of course, monolithic has more thermal bridges. I hardly know of any objective studies here, only the Fraunhofer one, which concludes that monolithic buildings more often have façade damage than ETICS buildings (I find that interesting, as it goes against the quite widespread opinion that ETICS façades are all eaten up by woodpeckers )

... many of the fashionable wall constructions with insulation boards have a total thickness over 40 cm, a 36.5 cm aerated concrete wall is equivalent.

Of course, I can make any wall "as thick as I want," but it was about the insulating property. With the same wall thickness, you can achieve significantly better insulation with ETICS.

I myself also have a significantly thicker wall structure, but that’s simply because we build double-shell. If we had built single-shell, Ytong would have been my last choice, although it would have been the cheapest option here with us. But then we’re back to the religious war again

It would be interesting to hear from again.

The site manager is completely right. We built our house monolithically from Poroton T8 with 43.5cm with perlite filling. From the inside, there was still 5cm of Ytong as an installation level for all kinds of pipes. 2 full floors + gable roof. However, the gable sides of the attic were built with 25cm Ytong. For the current attic conversion into a playroom, 80mm WEDI boards were glued to the gables (Toom tile adhesive for about €4.19 per bag). The rafters insulated with 200 Rockwool were clad with drywall. The sound insulation is the best in the entire house (except for the basement made of 30cm WU concrete). The weak points are always the transitions, e.g. from wall to window or door. If these are not properly foamed out and the appropriate foil is not used as a finish or the plaster does not properly overlap, the sound insulation is immediately zero. Also, the old roller shutter boxes built into the masonry are no longer appropriate for monolithic construction. One should use exterior boxes with electric drives. If you pay attention to all these things, the house can be built even from papier-mâché and still be soundproof. Of course, mass/density and multilayering are good, but it can also be done differently.

On the subject of mold. Mold does not arise from walls that are too dense but rather from stingy homeowners who do not heat properly and ventilate incorrectly, or from shoddy construction and thermal bridges, not from lack of warmth. Example. Cold air constantly flows under a poorly installed windowsill into the building and meets warm air. Warm air cools down and releases its humidity because cold air cannot hold as much moisture as warm air – condensate forms. Simple physics. The same happens with tilt ventilation and also with whistling shutter boxes. The whole thing + wallpaper, drywall, wood, etc. = food for mold. Water, nutrients, and room temperature – what else do you need to be happy, mold thrives. Water is the most important – without water no life. Our house is mold-free, the neighbor’s brick building is not. The highly praised glass wool in the air layer absorbs water and transfers it to the sand-lime brick masonry. There are whole puddles behind the brick in the Z foil. I still cannot understand what it is used for. When the neighbor opened the masonry sealed with the praised foils, a proper cloud of steam came out. It also makes no energetic sense to apply thermal insulation from the outside only to then heat the entire masonry. But that is another topic. A controlled residential ventilation system extracts the condensate from the air already in the heat exchanger and sends dry air into the room. Always fresh air and no condensate. Nevertheless, I perform daily shock ventilation.

Cold bridges, no warmth.

That alone disqualifies any building physics statements in your post.
There is no cold, only heat or a lack of heat. Accordingly, there are only thermal bridges.

If you pay attention to all these things, the house can be built from papier-mâché and still be soundproof.

That speaks true competence - however, no building physics expertise.