Short Answer You possess the statutory right to an immediate reduction in your monthly rent if a core building service like an elevator becomes non-functional. This legal mechanism, known as Mietminderung, arises automatically by law from the moment your landlord knows about the defect — but knowledge you cannot prove is knowledge you cannot enforce. What Most Expats Don't Realize You lived on the fifth floor and carried heavy groceries up one hundred steps for three consecutive weeks because the main building elevator was broken. You complained to the building manager over the phone and expected a retroactive discount on your next monthly invoice. When the discount never came, the landlord simply denied that any phone call had taken place — and with no provable notification date, your reduction claim for those three weeks collapsed, costing you €150 in unrecoverable rent value. What To Do * Email a formal written notice called a "Mängelanzeige" to your landlord the exact hour a building asset breaks down — the reduction runs from the moment he provably knows. * Download a template for rent reduction percentages to calculate the appropriate deduction based on current German case law before your next transfer. * "Ich mindere die Miete ab sofort wegen des Aufzugsausfalls." (I am reducing the rent immediately due to the elevator failure.) — include this explicit statement in your written defect notification. The Truth Germany's housing courts tie the practical value of rent reductions to the evidence of when the landlord learned of the defect. The right itself needs no special form — but the system quietly converts every undocumented phone call into a dispute you lose, which is why the tenants who get paid are the ones who put everything in writing.