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

...EIFS made of styrofoam crumbles at least just as much.

May be, this plays a rather minor role here (load discharge or input). Moreover, there are alternatives for this.

...Do you see differences in stability between aerated concrete, hollow bricks, and bricks filled with perlite or mineral wool?

The necessary stability of the load-bearing envelope is specified by the structural engineering, this applies to each of the mentioned variants.

...That would be at least 22,000 euros more in our case – representative hand-formed facing bricks not yet included. We do not want or cannot afford that, not even without golden door handles...

More compared to what? Moreover, it certainly always makes sense to invest in fundamentals and sustainability, possibly by sacrificing a few cubic meters of built-up space.
Here a general contractor / general planner is probably running a client deterrence service to "steer" the builder into their own concept.

...Nothing to understand.

Increasingly, with stricter energy saving regulations or KfW requirements, buildings get into trouble during the summer heat period. The reason is relatively simple: summer heat protection is treated very negligently. This results, especially in lightweight construction, in many cases in air conditioning systems having to be retrofitted – or you sweat! The necessary energy and investment effort for this was, of course, beforehand not taken into account. A knave who thinks ill here.
A calculation of cooling loads or room temperatures in the summer heat period usually does not take place. Also here a knave who...
The list of pointless money waste can be extended arbitrarily.
Those who, for example, rely on a heat pump as a heat generator can save themselves excessive insulation, depending on the source, since this is not helpful, for example, for hot water demand. For example, a photovoltaic system can lead to “zero cost” for heating plus hot water in the annual balance with regard to consumption costs. A pleasant side effect is that, with mounted photovoltaic modules, the cooling load is also reduced.
There are sufficient passive options (building construction) to possibly avoid necessary active cooling (technical refrigeration) in summer.

Best regards

Hello €uro, regarding the load-bearing wall, I just wanted to know from you what you meant by "The various 'crumb stones' are sometimes a joke.", especially since we plan to also build with crumb stones. My specific question: Given λ, in my opinion aerated concrete is cheaper than hollow bricks and that much cheaper than "modern" bricks with filling. I tend towards the most expensive option, but it can be justified neither statically nor financially. I had hoped you could provide some additional arguments here about "crumb stones"...

Your note about summer thermal protection and airtightness according to the Energy Saving Ordinance is helpful, but in my opinion the method of choice is a controlled residential ventilation system with heat recovery. Depending on ventilation behavior and insulation standard, it is possible to
a) save 50% or more of primary energy consumption,
b) cool a bit in summer, and
c) avoid mold completely.

What is your view? Wouldn't that be more efficient than investing money in photovoltaics and extracting money unsolidarily from non-photovoltaic owners via taxes or having them install questionable air-water heat pumps that would only be ecological if the electricity were produced ecologically in the first place?

....regarding the load-bearing wall I just wanted to know from you what you meant by "The various 'crumb stones' are sometimes a joke." especially since we plan to also build with crumb stones.

So, crumb stones are, in my opinion, especially autoclaved aerated concrete with λ < 0.1. Just take a drill and drill a hole with a 10 mm drill bit. Afterwards, measure the diameter. For heavy loads (introductions) expensive special dowels are required. If my fingernail leaves a lasting mark on the "stone," for me it is no longer a stone. High, internal building mass (storage capacity) is also not provided by this, which can have a noticeable effect in connection with the system technology.

....My concrete question: Given λ, in my opinion, aerated concrete is cheaper than perforated brick and much cheaper than "modern" bricks with filling.

Price comparisons are not easy. The free market is quite regionally differentiated. In the case of general contractors/clients, other rules apply as well.

.... Your reference to summer thermal protection and airtightness according to the Energy Saving Ordinance is helpful, but in my opinion the method of choice is controlled residential ventilation with heat recovery. Depending on ventilation behavior and insulation standard, this can save a) 50% or even more % of primary energy consumption,...

Primary energy is indeed quite helpful, but actually only interesting for verification procedures. What must be paid for is final energy! So how much final energy is saved? Overall a more than daring thesis. Please provide a concrete and comprehensible example for this. The actual cooling effect of controlled residential ventilation is mostly greatly overestimated. Not a few controlled residential ventilation systems must pause for a time in summer, despite bypass. In addition, one would have to know beforehand what cooling output is required and what can be provided by a controlled residential ventilation system. Example for this?

....What is your view? Would that not be more efficient than investing the money in photovoltaics and unsolidarily pulling money out of the tax pocket of non-photovoltaic owners or having dubious air-water heat pumps installed, which would only be ecological if the electricity was already produced ecologically?

The distinction between one’s own wallet, solidarity, and environmental conscience must be found by each person themselves. Not infrequently, builders discover their green conscience afterwards when it becomes clear that their concept has gone economically wrong. An air heat pump is by the way not dubious at all, but can definitely be the first choice, provided the conditions are suitable. Such sweeping statements are unrealistic and show little expertise. A well-planned air heat pump system achieves an annual performance factor ~3.5, possibly somewhat better. With an assumed annual demand of 10,000 kWh for heating and hot water, approximately 2,857 kWh are drawn from the grid, the rest is supplied by the environment. With a gas condensing boiler, I have to get about 12,500 kWh from the supplier. So 9,643 kWh more. Best regards NB: Forum chats do not replace necessary planning, sizing, or consultation. At best, they can encourage reflection, nothing more!

Hello €uro, thanks for the info about the stones with λ < 0.1! I’ll get myself a few stones...

Overall a more than bold thesis Please provide a concrete and comprehensible example for this.

Example:
Region: Berlin, heating period mid-October to end of April,
170 sqm area, 2.50 m room height.
Air exchange 0.5/h (recommended minimum): heat loss: 5889 kWh per heating period
At 80% efficiency, (theoretically) 4711 kWh could be saved – minus the kWh for the fan motor...

How do I come to this?
A small hint: please google "heat demand" and "u-value" and you will be helped.

By the way, an air heat pump is by no means questionable, but can actually be the first choice, provided the framework conditions are suitable Such general statements are unrealistic and show little professional understanding.

Thanks for the compliments. Professional expertise is indeed not present, merely knowledge read off about building physics and technology.

A well-planned air heat pump system achieves a seasonal performance factor of about 3.5, possibly somewhat better.

Exceptions prove the rule (seasonal performance factor <=3)? When I google field tests, I always find significantly worse values than manufacturer specifications... Where is the truth?

With an assumed annual demand of 10,000 kWh for heating and hot water, 2857 kWh are drawn from the grid, the rest is supplied by the environment. With a gas condensing boiler, I have to draw about 12,500 kWh from the supplier. So 9643 kWh more.

With what efficiency do the fossil power plants produce their energy? 40-45%? How much loss remains in the lines? (6 or more %)

Oh, always this question about the right building material. There are those who swear by aerated concrete (many greetings to Bauexperte), then there are those who like bricks. And there are actually still people who prefer the use of calcium silicate bricks. All stones have their advantages and disadvantages.......
If it should have good insulating properties, then aerated concrete is certainly a good thing, which, however, and this is where building physics comes into play, comes at the expense of sound insulation. Mass is and remains the basic requirement for good sound insulation. You also have to make compromises with aerated concrete when it comes to summer heat protection, because here, too, mass is a basic requirement. In addition, aerated concrete is not to be rated as ideal for point load transmission statically.

I am also not a fan of ETICS. This should only be used in renovation after thorough planning. A massive and solid construction method is, in my understanding, the two-shell wall structure with facing. Apart from the somewhat higher costs, I know no disadvantages of such a construction method.

Who chooses which building material depends on what is important to them. Sound insulation, thermal insulation, summer heat protection, load transfer (in complicated constructions). Blanket statements like aerated concrete, brick, or calcium silicate is the best material don’t work. It always depends on needs and requirements.

I have to admit, however, that I see the most advantages in calcium silicate brick. And in the end, of course, all components as well as the system technology must be coordinated with each other.

Regards

...Air exchange 0.5/h (recommended minimum): Heat loss: 5889 kWh per heating period At 80% efficiency, (theoretically) 4711 kWh could be saved - minus the kWh for the fan motor...

Then just believe this nonsense By the way, the waste heat from the fan motor is utilized!

...Small hint: Please google "heat demand" and "U-value" and you will be helped.

I know these sites. They cause more harm than good.
Then get a written guarantee from them for this rubbish. However, I suspect that there will be nothing A knave who thinks evil of it.

...professional expertise is indeed not present, merely recited knowledge about building physics and technology.

That has not gone unnoticed.

...Exceptions prove the rule (annual performance factor <=3)? When I google field tests, I always find significantly worse values than the manufacturer’s specifications... Where is the truth?

Manufacturer’s specifications have absolutely nothing to do with real practical systems. These field tests sometimes include every deadly sin of failed or non-existent planning/dimensioning. Manufacturers are often unjustly taken to account here. They had no planning contract whatsoever! If some tradesman or general contractor cobbles something together, the manufacturer of a device cannot be held responsible for it.
Whoever thinks that modern system technology can be used without solid and exact basic assessment, planning, and dimensioning for highest energy efficiency is mistaken. They should rather choose an open wood fire as a heat generator!

...With what efficiency do fossil power plants generate their energy? 40-45%? How much loss remains in the lines? (6 or more %)

Who actually cares about that? For the vast majority of my clients, their own shirt is closer than their pants, and I can't even blame them for that; I can even understand it.

v.g.