Kernrechtsfrage
Whether accessory charges not clearly listed in the written lease could be charged to the tenants
Extrahierter Entscheid
Only accessory charges specifically agreed in the lease could be imposed; the disputed additional charges were not owed.
Extrahierte Begründung
Art. 257a(2) CO requires a specific agreement on accessory charges. Conduct over many years cannot replace the lack of a sufficient contractual basis, and later acceptance of invoices without the official procedure cannot amend the contract against the tenants.