House built in allotment garden without building permit (year 1920)

Nordlys: If the object was never referred to as a house, then the matter would be clear to me as well. The municipality speaks of a single-family house. The land register refers to a residential building. All fees and taxes are declared for a residential building. However, if I now want to use the single-family house as a "house," then suddenly it is no longer a house.