Additional interior insulation warehouse

I should probably have added a few more details. The floor will be completely rebuilt with insulation and underfloor heating. The roof of the hall has just been modernized and insulated. The ceiling is a reinforced concrete slab. On top of that, in the next step, another apartment for my children will be created. Permission for both is already granted.

Hello,

how exactly has the roof structure been constructed? Is there an eaves overhang above the existing facade? Pictures from the outside?

You write that the conversion is approved. In that respect, you should have also specified a wall structure when submitting the plans, right?

That's the problem. No one dares to tackle it. Everyone is afraid of condensation.
The idea then was to remove the old sheet metal and rebuild with a completely new outer wall structure.
But we're talking about 7-meter-high walls.
That can't be the only solution

They are not only afraid of condensation but probably also of such a wall, 7 meters high! You can't just build that straight up without having clarified the structural/static requirements.
Even a wall made of OSB etc. can't be built however you like, the same things must be taken into account.
The sheet metal wall of a storage hall is allowed to move or dent a bit, but certainly not in living spaces.

I am aware that I cannot achieve perfect insulation with the existing construction.
.....6cm flexible wood fiber.....

Are you thinking of underfloor heating? I actually believe that with regard to insulation you first really need to significantly up your game.
I don’t know if I am misunderstanding this whole thing, but an approved residential building with another apartment for the children and an outer wall with less than 10 cm (6 + OSB) material.....??

It is an approximately 1200 sqm warehouse with a flat roof. No roof overhangs. A change of use was applied for and approved. The rules are probably a bit simpler here since the rooms already existed and were previously used as offices. That doesn't change my problem now anyway. The structural engineer would have insulated from the inside with 10cm. I would have been a bit more cautious to avoid moving the dew point too far inward. There is already insulation present. About 6 cm in the existing wall. My question is how I can now optimize this most effectively. It may be that someone here has already done something similar.

Therefore, here is the question of how to make the best of it without bringing moisture/mold into the wall.

The question could be solved with a controlled residential ventilation system with automatic humidity regulation.
Also consider air conditioning/split systems,
the hall will probably be cold in winter and very warm in summer.
Construct the wall in multiple layers like prefabricated houses,
i.e. for statics and thermal insulation.

I can confirm that. The office rooms were used as storage for about 4 years. The heating was never on during this time. There was never any frost, but of course warm in summer. Controlled residential ventilation has also already been suggested to me. Due to the air exchange, there is less risk of moisture. If I understood correctly, the metal sheet inside is the main problem. There simply can be no exchange to the outside.