Extension options under §34 of the Building Code

Correct - the entire settlement is called "Maikäfersiedlung"

Are there still houses without an extension there?

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Is the extension to the adjoining terraced house recorded as a boundary building (presumably mutual) in the land register? Over what length? Height?

The building line towards the street has been consistently observed so far. Also by the new buildings (Höhenstadter-Straße). It may well be that the building authority does not want this alignment to be interrupted here. Probably the only way is to ask directly there!

The REH has only 1 full floor ground floor, attic, and loft? Are there floor plans, elevations, or photos? From all 3 sides?

The boundary construction is currently not secured/recorded in the land register. Section II is free of encumbrances. In the plans from the year 2000 (=current condition), the whole looks as follows: