Retrofit chimney and connect stove pipe on the first floor

If a wall is also a component, that is not correct. Our stove pipe goes from the living room through the hallway wall and continues in the hallway to the chimney. The chimney sweep approved it that way last year. I can only say regarding the original question: call the chimney sweep and have it decided on site.

The renovation was not approved for us last year. We wanted to move a stove into the adjoining room and run the pipe through a wall, but it was not allowed. However, we also have timber frame walls.

We were not granted permission for the conversion last year. We wanted to move a stove into the adjoining room and run the pipe through a wall, but it was not allowed. However, we also have timber frame walls.

Then it depends on the construction method. The pipe must maintain certain distances from combustible materials. That is certainly not guaranteed there. It just shouldn't be generalized. We have stone walls; that is no problem at all. Interestingly, gypsum board is also a non-combustible building material.

Correct. Two times GK makes F30 (at least in the past)

Correct. From 2x GK you make F30 (at least in the past)

Which sounds strange to me as a layman, since the stuff consists of cardboard on the outside.

Visually, I find your stove pipe questionable at first. First, you have to have the draft of the chimney calculated. Adapted to your stove, the expert report will then also calculate the diameter for your chimney and the stove pipe. It’s no good if the chimney sweep gives his approval and the stove does not draft. You also cannot enter the chimney at the lowest point with the stove pipe. Just have a chimney installed through the ceiling. From the floor up. That doesn’t cost much more anyway; you have to do the roof penetration anyway. My practical tip. Find a chimney builder, they often also make the expert reports for the room air and dimensions. They know more than a chimney sweep. I also once had problems with a chimney or the heating in one of my properties. The chimney builder made me such a report for about 50 euros. After that, we built. And the chimney sweep also wanted that report.