Distance area between two buildings

Hello,
I am currently planning the house. I am very interested in the topic of distance areas between two buildings.

Building A (Blue):
New residential building
Exterior wall 36cm; Two full floors + gable roof; There is no window on the ground floor in the green area

Building B (Orange):
Empty machine hall; approx. 5m high; exterior wall approx. 30cm (cement stone); 1 small window facing south (red marking);
Located directly on the property boundary
I would currently say that the southern wall is not a fire wall.

I would be interested to know what distance I probably have to maintain to building B? Would it help me at all if the southern wall (building B) is made into a fire wall?

I am not expecting a 1000% correct answer here (with § etc.). The measurements on the picture are also not entirely correct. Just your opinion.

Empty machine hall; approx. 5m high;

And that was allowed ON the property boundary???

The two plots were previously one (belonged to my parents-in-law). The southern plot was transferred to us (divided). The boundary was then drawn there. This means that the machine hall was already there before.

Oh, so you also own Hall B. How about tearing it down if it's empty? Minimum distance can vary depending on the region. With two full floors + gable roof, it will definitely be more than 3 meters. I would just take the plan to the building service and they can quickly say whether it is basically approvable, or what the distance areas have to be like.

So the hall is on the property of the parents-in-law. So it does not belong to us. They wanted to keep it and also use it (I think as storage space).

Definitely more than 3 meters.

Bauservice = District office?

Setback areas and firewalls are two different things. I would also recommend going to the office or consulting an experienced architect with contact at the responsible office.