A rent increase is not communicated by ordinary letter. It must be notified on the official form approved by the canton, give reasons, and reach the tenant at the latest ten days before the start of the notice period. Three cumulative conditions: if a single one is missing, the increase is void.
The reasons cannot be limited to a general formula. The landlord must state what the increase is based on: a rise in the mortgage reference rate, inflation, value-enhancing works, alignment with rents in the district. A mention such as “market adjustment”, with nothing further, is regularly set aside by the courts.
The period for challenging is thirty days from receipt of the form. The challenge is filed in writing with the district conciliation authority, free of charge. After those thirty days the increase stands, even if it was poorly reasoned: the nullity must be invoked, it is not established of the court’s own motion.
One point few tenants know: the same official form is required when a new lease is concluded in municipalities where the canton imposes it, Lausanne among them. If you move in and the previous rent appears nowhere, you may challenge the initial rent within thirty days of receiving the keys.
Do the arithmetic before challenging. An increase of CHF 60.– a month is CHF 720.– a year and will stay with you for the whole term of the lease. Conciliation, on the other hand, is free and is usually settled in a single hearing.