Question juridique clé
Whether the cantonal court could adjust the rent reduction for defects and its starting date under Art. 259d CO
Solution extraite
The cantonal court correctly held that rent reduction starts only once the landlord is aware of the defect and may be adjusted according to the number and weight of defects proven.
Motifs extraits
A rent reduction must be proportional to the objective value of the premises with and without defects. If fewer relevant defects are established on appeal, the reduction must be reduced accordingly. The court did not replace equitable discretion unlawfully.