Ventilation system in the new building, yes or no?

The ventilation system saves around 12 to 18 kWh/m²/a at an efficiency of 80% (90% is already possible) with a self-consumption of about 4.5 kWh/m²/a.

Oh. If we calculate with a gas price of 4.5 cents / kWh and an electricity price of 16 cents / kWh, which is rather cheap, then financially it is a zero-sum game and that with investments of around 9000€. That means economically there is nothing at first. The electricity price must fall, the gas price rise, and the apartment be warm enough so that heating energy consumption increases... 9000€ already creates an interest burden of 340€ p.a. when building. And regarding CO2 savings?... If electricity is generated with a power plant efficiency of 40%, then it requires 4.5/40% = 11 kWh of primary energy to save 12-18 again, difference optimally 18-11=7, times 160 sqm = 1120 kWh. Well, at least. The all-important question remains whether you really absolutely need this to avoid moisture problems. Had a short conversation this morning with an expert who said that even among professionals opinions differ because the overall experience is still quite limited, especially when it comes to long-term statements.

The all-decisive question remains whether one really absolutely needs that to avoid moisture problems. Had a short conversation this morning with an expert who said that even among professionals opinions differ, because the overall experience is still quite limited, especially regarding long-term statements.

That is the problem. I would always recommend ventilation with a diffusion-tight wall such as KS, Poroton with Styrofoam as insulation, prefab houses with OSB wall or wind-tightness foil. Without ventilation it works with diffusion-open walls like Ytong, Hebel, 36 cm Poroton without external insulation, prefab houses with a special wall construction without foil. Here the house can "breathe", and if it is also well ventilated, for example all night long, then everything is fine.

That is the problem. I would always recommend ventilation for a diffusion-closed wall such as KS, Poroton with styrofoam insulation, prefabricated houses with OSB walls or windproof membranes. Without ventilation, it works for diffusion-open walls like Ytong, Hebel, 36 cm Poroton without external insulation, prefabricated houses with a special wall construction without membrane. Here the house "breathes", and if well ventilated, for example all night, then everything is fine.

That houses or walls "breathe" is probably a myth, which is repeatedly spread anew without corresponding to the truth! Before making such a statement, one should be more solid in building physics!

Best regards

Okay, they obviously do not breathe, hence the quotation marks. It is meant, of course, that air exchange is possible.

Are all the others stupid?

Before making such a statement, one should be a bit more solid in building physics!
best regards

What is your problem with answers from other forum members? Answer the question and that's that. Don't make the questioner look like an idiot who is too stupid to judge for themselves!

First of all, diffusion and respiration are two different things.
A wall could be air-permeable; for that, it must be thin and porous or full of holes, which can probably be denied for normal walls. Diffusion occurs if it is not hindered by building materials like concrete or foil, but diffusion, especially through thick walls, is a slow process that, in my humble opinion, is not suitable for continuously disposing of large amounts of moisture.

What remains is the air exchange through door gaps, window leaks, etc., which is also required by the Energy Saving Ordinance to keep CO2 and O2 in the breathing air at an acceptable level. In the blower door test, the value 0 is not reached. The question is whether this air exchange, together with normal ventilation behavior, is still sufficient to keep the moisture out.

There are actually enough voices on the internet who have built without controlled residential ventilation and not all of them tell of mold in the house.

PS – It must be possible that two people hold different opinions here without it becoming personal...?