Key legal question
Whether the apartment suffered from a serious defect under Art. 259b lit. a OR after the arson attacks
Extracted holding
Yes. The repeated arson attacks created an objectively intolerable situation and endangered the tenants' and their children's mental health.
Extracted reasoning
A serious defect exists when the use of the dwelling is substantially impaired or objectively unreasonable. Threats to physical or psychological health always qualify; third-party disturbances can also constitute such a defect.