Kernrechtsfrage
Whether the tenant proved defects attributable to the landlords and a reduction in use justifying rent reduction under Art. 259d CO.
Extrahierter Entscheid
The defects were proven, attributable to the landlords, and did restrict the use of the premises; the rent reduction was therefore justified.
Extrahierte Begründung
The cantonal court relied on expert evidence and witness testimony to find water infiltration and odor problems originating from the building and ventilation system, not from the tenant. The reduction rate was an assessment question and was not shown to be arbitrary.