A distinction shall be operated between costs incurred in order to remedy a defect and those related to the renovation of the rented apartment.
According to Art. 259 I CO, the tenant must remedy defects which can be dealt with by minor cleaning or repairs as part of regular maintenance and, depending on local custom, must do so at his own expense.
Defects which can not be qualified as minor, such as water infiltration for example, are to be taken in charge by the landlord. This applies also to any costs incurred in connection with normal wear and tear.
The law gives different options to a tenant facing defects that he should not be responsible for. He may require the landlord to repair the object, to reduce the rent proportionately, pay damages and even assume responsibility for litigation against a third party (Art. 259a I CO).
The tenant must, in writing, set the landlord a reasonable time in order to remedy the defect and may warn him that, in the event of failure to comply, on expiry of the time limit the tenant will deposit his future rent payments with an office designated by the canton (Art. 259g I CO).
Renovations of the premises are, in principle, charged to the tenant, generally by increasing the rent of the premises. The landlord may renovate the premises provided that the renovation works can be supported by the tenant and the lease has not been terminated. In carrying out such works, the landlord must give due consideration to the tenant’s interests (Art. 260 CO).
Renovation undertaken directly by the tenant may be carried out only with the written consent of the landlord. At the end of the contract, if the object has appreciated significantly in value as a result of the renovations, the tenant may claim appropriate compensation for such appreciation (Art. 260a CO).