Facts
The complainants, [X.] and [Y.] , are tenants of a 4 1/2-room apartment in Basel. The rental agreement of January 31/February 3, 2000, contains a provision whereby the tenants must pay CHF 260.-- per month "à Kto. operating costs". The contract refers to the "General Contractual Terms for Rental Agreements for Apartments" (AVB), which contain a list of ancillary costs.
The tenants have settled two ancillary cost statements for the years 2000/2002 and 2002/2003, but have not paid the third statement for the period from July 2003 to June 2004. They argue that the ancillary costs were not validly apportioned and are therefore not owed.
The Court of Appeal of the Canton of Basel-Stadt dismissed the tenants' complaint and found that the parties had unequivocally and consistently agreed on advance payments for operating costs, which were specified in the AVB.
Considerations
The Federal Court has upheld the constitutional complaint of the tenants and reversed the judgment of the Court of Appeal. It found that the Court of Appeal had acted arbitrarily in assuming that the tenants, by paying the ancillary cost statements, had acknowledged a actually existing consensus between the parties regarding the ancillary costs to be borne by the tenants.
The Federal Court has stated that an originally existing actual will of the parties regarding the ancillary costs to be borne by the tenants presupposes that the parties had exact knowledge at the time of conclusion of the rental agreement of which costs were to be taken over by the tenants. Since the Court of Appeal found that it was not originally clear to the tenants what exactly they had to pay, it cannot be…