Ceiling suddenly too small for controlled residential ventilation!

I think Katja's draft is good. But you will be charged extra money for the change in the planning.

What is a Fensterfalzlüfter, are those the little knobs at the bottom of the window frame?

Google RegelAir. Look at the pictures.

No offense, but the window rebate is just energy nonsense. You build an insulated, airtight house and then have windows with holes installed so that ventilation is available. I also like Katja's design, I would suggest that to the general contractor if you like it yourself.

Apart from that, I am an advocate of [Kontrollierte-Wohnraumlüftung]. We have gas + [Kontrollierte-Wohnraumlüftung] ourselves. Without solar, which is the next crutch economically speaking... We have a demand of ~9kWh per day for hot water. At 6 cents/kWh, that's about €200 per year. With a solar system, I save about 2/3 of that upfront. So around €150. With systems starting at €4000, everyone can calculate for themselves how long it takes to pay off. Even if I assume a heat demand of 15kWh/day (there are only two of us), it still takes over 20 years for anything to actually pay off.

If this can be reconciled with the energy saving ordinance, I would insist on gas + [Kontrollierte-Wohnraumlüftung]. Without solar, there's the additional problem that you save on the buffer tank. Given your space problem, that's not the worst...

Thank you very much for the information. I don’t think the floor plan is bad either; I already asked my wife about it yesterday, but she had some objections. I will have to discuss it with her in more detail! You definitely need to submit a tectonic report to the authorities, right? The window of the guest WC would then be somewhere else... The foundation slab has not been poured yet; they should start digging today.

According to the Energy Saving Ordinance, gas + controlled residential ventilation without solar is possible, that was the whole plan! (What we save by leaving out the solar, we don’t know yet)

matte, a controlled residential ventilation system is economically just as much Harakiri. You spend 10 thousand to have good air, but you can achieve that with 1200,- for exhaust fans and [regel air] as well, for that you need 25,- euros more gas per year, but significantly less electricity, because the controlled residential ventilation system is electric, the [regelairs] purely mechanical. Unfortunately, the energy saving ordinance forces us to live in plastic bags and to upgrade them with some stupid eco-technology that never pays off. No matter whether controlled residential ventilation or solar....k.

The guest WC window would then be somewhere else...

I would first be concerned about the supply and drainage lines... which would have to be connected through the base slab. If they're already digging, that would be tight. What about the suspension proposal from Yvonne?