ᐅ 36 cm Ytong exterior wall, solid construction, mold formation, insulation

solu15 schrieb:
...I have now read through the entire thread, BUT there doesn’t seem to be a clear, simple answer to the question, or I might have missed it.

Such an answer is not possible unless the person responding has clairvoyant abilities.

solu15 schrieb:
...Since I also have 36cm (14 inches) Ytong, built in 1980, I’m simply asking again here: Does additional insulation make sense? At least on the north and weather-exposed sides? So far, I have had no mold, moisture, or ventilation issues.

An energy consultant from the insulation industry will always answer this question with a definitive YES. However, the actual situation is much more complex.
In theory, additional insulation reduces energy demand, but to what extent depends on the starting conditions. Building physics aspects also play a role (vapor permeability of the outer finish, e.g. render). If condensation occurs, the theoretical insulation effect exists only on paper. The same applies to the heating system. With a brine heat pump as the heat source, the measure will likely bring only marginal benefits. With a combustion-based heat source, e.g. oil or gas, it might theoretically be more effective. However, if the heat source was already oversized, adding insulation can actually worsen the annual efficiency of the system. The intended energy savings usually only partially materialize in practice, so it’s worth asking whether the actual result justifies all the effort. Additional insulation often requires adjustments to the heating system.

solu15 schrieb:
...Please keep answers focused and don’t digress. Thanks!!!!!

You probably won’t get the truly valuable “ultimate solution” for free in just a few words.

Best regards.

Thanks €uro, that’s at least an answer I can understand.

Just a quick calculation shows that the exterior wall – using the best currently available Ytong plan block – has a U-value of 0.21 W/m²K.
I have no affiliation with the company Ytong.

olali2 schrieb:
Hello, we have now received a quote from a general contractor for our planned single-family house, which we actually liked.

However, a prefab house builder told us that if you build with solid construction, you should definitely also install insulation, otherwise mold problems will occur.

What do you think? KfW standards are not relevant here.

I would change the general contractor. Anyone recommending a 36cm (14 inch) Ytong block for the exterior wall is rather questionable.
Ytong absorbs water like a sponge. That leads to construction damage.

Better to use 36cm (14 inch) bricks. With a standard plaster finish (inside and outside) there is no mold formation—unless you don’t ventilate enough. This method has proven reliable; otherwise all the old master builders would be idiots and half of Germany would be moldy?

kamnik schrieb:
Anyone recommending a 36 cm (14 inch) Ytong block as an exterior wall is rather questionable. Ytong absorbs water like a sponge. Building damage guaranteed.

This rumor, often presented as an unchangeable fact, is very persistent.
Have you ever submerged a piece of aerated concrete in water for a few hours? If not, you should try it—you might be surprised.

Kind regards

Hello,
kamnik, the statements you are making here in the forum are simply unbelievable. I find them quite amusing.
Surely every planner (by the way, are you from the construction industry?) has their favorite materials. I don’t prefer aerated concrete blocks either, but to say outright that they are rubbish and that building defects are inevitable is even worse nonsense. And to claim that bricks, just because they have been commonly used throughout history, are the ultimate solution does not exactly demonstrate professional expertise either.

You can use both aerated concrete and bricks without causing any building defects. Choosing the right building material requires a deeper understanding of construction technology…

Regards