ᐅ What counts as attic floor area under the two-thirds rule?

Hello dear forum members,

I hope you can help me with my issue.
We are currently planning to build a single-family house in Barnim/Brandenburg and are unfortunately quite restricted by the development plan. According to it, construction must be single-story with a pitched roof or hip roof at an angle between 30 and 50 degrees. The eaves height is specified as a maximum of 4 meters (13 feet). The ridge height is not defined. When determining the number of full stories, the building authority applies the two-thirds rule.

Our planned house (ground floor and upper floor) has a length of 13 meters (43 feet) on the eaves side and 10.5 meters (34 feet) on the gable side. Now we want to make the house look as modern as possible and have planned a flat-roof dormer about 4 meters (13 feet) long in the middle of one eaves side.

My question is: If there is only an open space/gallery in this dormer connecting the upper and lower floors, is this still counted as usable floor area in the attic that is above 2.30 meters (7.5 feet)?

This would, of course, significantly increase the square meter number of the attic floor area over 2.30 meters (7.5 feet). As a result, the knee wall would shrink to a narrow 0.5 meters (1.6 feet), and the area in the attic rooms under 2 meters (6.6 feet) height would protrude about 2 meters (6.6 feet) into the rooms, which is very unsatisfactory for us in terms of space.

Is there a clear regulation on what is counted as floor area in the attic when applying the two-thirds rule?

I look forward to your advice and thank you for your efforts!

Best regards,
Thorsten

This is clearly a question for the architect responsible for planning. I hardly think you will get an answer here that has any legal validity. You cannot rely on opinions in this context.