ᐅ Aerated concrete or calcium silicate masonry with external wall insulation system (EWIS) using polystyrene foam

Depending on the builder and region, sometimes one option is cheaper than the other.

The answer is always the same: use the material your builder normally works with, meaning the one they have more experience with. Correct installation is far more important than the material itself.

And don’t worry: it has zero impact on living comfort or indoor air quality. The airtightness in a house is ensured by the interior plaster, not by the wall material or insulation. You need to ventilate exactly the same way with both approaches, whether manually or automatically. Airtightness is legally required in Germany, so there’s no alternative.

If you’re concerned about the durability of external thermal insulation composite systems (ETICS) / external wall insulation (EWI), the Fraunhofer Institute has the answer: they are just as durable as masonry alone.

The myth of facade damage persists stubbornly, but that’s also addressed in the study. In fact, ETICS facades tend to show fewer damages, possibly because they have fewer thermal bridges compared to aerated concrete walls.

If soundproofing is an important topic for you, then calcium silicate bricks combined with ETICS are a good choice. The downside, as Karsten mentioned, is that you need special anchors for mounting items like lamps on the exterior. However, these fixtures also hold for a very long time.

If you’re concerned about health and ecology, focus more on the items you come into direct contact with using similar materials: toothbrush, yogurt container, sofa, bed, and so on.

So if Ytong is even more expensive, I would clearly choose the other option. Usually, the price is the other way around!

@Tego12: Thank you for your very informative post.
P.S.: Yogurt containers are already made of glass.

Tego12 schrieb:

As Karsten mentioned, a disadvantage is that special anchors are needed for exterior installation of items like lamps. However, they hold securely for a very long time.

These anchors cost 20€ for 50 pieces on Amazon. You drill briefly through the plaster and reinforcement mesh with a fine drill bit and then screw in the anchor with just a few turns. You can even skip pre-drilling with a bit of pressure.
I would say I have never inserted an anchor into a wall more easily. They are more than strong enough for lamps, mailboxes, and similar fixtures. Different systems are required for awnings, but those are usually installed by professionals and the process is similar with aerated concrete or clay blocks.

No offense to aerated concrete, but given the price difference, the choice is clear. With the savings, you can have the facade painted three times—if it really turns out that the external thermal insulation composite system (ETICS) facade is more prone to algae or dirt.

Nordlys schrieb:

Awnings

Awnings are preferably mounted to the ceiling cavity rather than directly to the masonry.
Whether you should trust a much denser sand-lime brick less than aerated concrete, well, both are definitely possible.

We may soon face a similar decision.

Our preferred option offers insulation for the calcium silicate bricks in addition to expanded polystyrene (EPS), such as mineral wool or wood-based insulation—each at an increasing additional cost.

From what I have read, mineral wool performs well—less prone to mold and moisture issues, excellent fire protection—although the EPS boards also have high fire resistance. Only the insulation value is slightly lower, but mineral wool has a longer lifespan.
We still need to verify whether this is actually better, as there are always different opinions and claims on the subject.