Aerated concrete or sand-lime brick with external thermal insulation composite system (ETICS) made of polystyrene

It depends on the developer and the region, sometimes one thing is cheaper, sometimes the other.

The answer is always the same: take the material your developer normally uses, in other words what they have more experience with. Proper installation is far more important than the material.

And don’t worry: it has zero impact on the living quality or the air. The airtightness in a house is ensured by the interior plaster, not the stone or the insulation... You have to ventilate exactly the same with both concepts, whether manually or automatically. Airtightness is mandated by law in DE, there is no other choice.

Are you afraid of the durability of WDVS? The Frauenhofer Institute has the answer: no less durable than just stone.

The myth of facade damage also persists stubbornly... But the study provides answers here as well... Tendentially, WDVS facades actually show fewer damages... One reason could be the lower number of thermal bridges compared to a aerated concrete wall.

If sound insulation is an important issue for you, then sand-lime brick plus WDVS. The disadvantage, as Karsten mentioned, is that for exterior mounting of e.g. lamps you need special anchors. But it also holds everything for ages.

If you are concerned about health and ecology, think more about the points where you come into direct contact with similar material: toothbrush, yogurt cup, couch, bed, ...

So if Ytong is even more expensive, then I would clearly choose the other alternative. Normally, the price is the other way around!

: Thank you very much for your very informative post. P.S.: Yogurt cups are already made of glass

The disadvantage, as Karsten mentioned, is that for exterior mounting of, for example, lamps, special anchors are needed. However, everything stays attached forever.

These things cost 20€ for 50 pieces on Amazon. You drill briefly through plaster and reinforcement with a fine drill and then screw in the anchor with a few turns. You can even skip pre-drilling with a little pressure.
I want to claim that I have never put an anchor into a wall more easily. More than enough load-bearing capacity for lamps, mailboxes, etc. Other systems are needed for awnings, but a professional takes care of that anyway, and it’s no different with aerated concrete or porous brick.

Nothing against aerated concrete, but with the price difference, the choice is clear. For the difference, you can have the facade painted three times, provided it really turns out that the ETICS facade is more prone to algae/dirt.

Awnings

Awnings are preferably mounted in the suspended ceiling rather than in the masonry.
Whether you should trust a significantly firmer sand-lime brick less than aerated concrete, well. Both are possible anyway.

We may soon be facing a similar decision.

So our favorite offers rock wool or wood-based insulation instead of Styrofoam for the sand-lime brick - with an additional cost increasing accordingly.

I have read that rock wool performs well - less prone to mold, moisture problems, best fire protection - although the boards made of Styrofoam also have high fire protection, only the insulation value is slightly lower, with a longer lifespan.
Whether this is really better we still need to verify, as there are always different opinions or applications here.