Features of a detached granny flat

I suspect your manufacturer is talking nonsense.... just suggest to him to do without the second controlled residential ventilation for the granny flat if both controlled residential ventilations cannot be installed in a shared technical room...

That is probably not technically possible. I have asked the house manufacturer to provide me with written sources proving that the unique selling point is lost with the KfW and the tax office. Let's see what they say about it.

That is technically not possible.

Technically, that is very much possible... it has always been done that way ^^

Maybe you need a controlled residential ventilation system with heat recovery to meet KfW55 standards, or your planner must ensure a proper ventilation concept... but there are also alternatives...

With this, I just wanted to show you that the controlled residential ventilation system actually cannot prevent it from being considered an independent residential unit, since you could also simply build without a controlled residential ventilation system... Or where should it say that a granny flat requires a controlled residential ventilation system?

Yes, you're right. You probably need a second controlled residential ventilation because the main apartment is about 150m² and the granny flat is about 52m². The builder argued that the filter would have to be changed, etc. Let's see if they deliver anything or give in.

A second controlled residential ventilation system is probably needed because the main apartment is about 150m² and the granny flat is about 52m²

No, one would be enough... there are sufficiently powerful devices...

The reason for the separation is more the control... For example, if you have guests in the evening and set the controlled residential ventilation to the highest level, your tenant in the granny flat might not be able to sleep because the high airflow creates noise at the vents...
or if you are a smoker and your tenant isn’t, then he won’t have your ash stuck in his filter etc...

The builder just argued that the filter would have to be changed etc.

Yeah, that’s true... and I actually think it’s better if the landlord always does it for both devices... So rather a plus for having two devices in one technical room!
I wouldn’t want to trust my tenant to regularly clean and change the filters... he might not care if the unit needs a complete overhaul after a few years....

Let’s see if they deliver or give in.

??? Who’s paying for that?

Yes, you're right. I do have to bring the money. I really wonder why they insist so much on that solution. There is enough space in the utility room in the main apartment, it would even be wasted because it is upstairs and therefore has a sloping roof. The controlled residential ventilation would fit there. So it would be very beneficial for the granny flat. I don't know why they are resisting so much. If KFW or the tax office really had a problem, that would have been the deal-breaker for a shared utility room. I will write to you about how it turns out.