Here is the excerpt from the BP:
Roof structures in the form of shed dormers, gable dormers, or cross-gabled extensions (cross gables and cross houses) are permitted for roof pitches from 30° onwards. The sum of the individual widths must not exceed 50% of the total ridge length of the building, but not more than 5m individual width. With gable dormers, the roof pitch of the main roof must be maintained. The ridge of the roof structures must be at least 0.8m lower than the ridge of the residential building. Roof cutouts are not permitted. Therefore, I have to revise my own statement. I was at 3m gable, but I am allowed to go up to 5m. That makes things more comfortable. Then a desk will fit in too : )
I still haven’t really understood how high the maximum knee wall can be.
Knee walls are only permitted for II=I+D buildings and up to a maximum of 75cm, measured from the top edge of the raw ceiling to the underside of the rafter at the outer edge of the wall. Since that is the outer edge and the roof rises at a 45° angle plus the wall thickness + now 30cm = 76cm, inside that is 1.5m - ceiling/floor construction = 1.1m. (I hope so : )
Best regards