Mold creeping across a bedroom wall, heating that fails in January, a leak the landlord ignores for weeks, these are among the most stressful parts of renting anywhere, and tenants often feel powerless. In Germany, you are not. The law gives renters substantial rights when a flat has serious defects, including the power to reduce your rent until things are fixed. But those rights come with responsibilities and a correct procedure: you must report defects properly, you have a duty to ventilate and heat to prevent mold, and you cannot simply stop paying. Knowing exactly where you stand, your rights and your duties, turns a miserable, helpless situation into one you can actually resolve.
This guide covers mold and repairs in a German rental: when you can reduce rent, whose fault mold is, your duty to ventilate, and how to handle a landlord who won't fix things. Your rights, used correctly.
When you can reduce your rent
German tenants have a powerful tool: rent reduction (Mietminderung) when a defect significantly impairs the flat.
When it applies:
- A defect significantly impairs the use of the flat
- Including mold, broken heating, persistent water damage, or other serious disrepair
- The reduction's size depends on how badly the defect affects living there
So if your flat develops a real problem, mold spreading, no heating in winter, a leak making a room unusable, German law lets you pay less rent until it is fixed, proportionate to how much the defect harms your living. A minor issue justifies a small reduction; a room rendered unusable or a flat with serious mold justifies a larger one.
But, critically, there is a correct process:
- You must report the defect to the landlord first
- Follow the proper procedure
- Do not simply stop paying, that can put you in breach
So Mietminderung is a genuine right, but it is not "the flat has a problem, so I'll pay what I feel like." It requires reporting the defect, giving the landlord the chance to fix it, and reducing rent correctly and proportionately. Done right, it is strong pressure on the landlord; done wrong (just withholding rent), it can backfire on you. This sits within Germany's broad tenant protections, and the reduction relates directly to the rent you pay.
Whose fault is the mold?
Mold is the most common, and most disputed, defect, because fault depends on the cause.
- If mold results from a structural defect, poor insulation, building faults, leaks, it is generally the landlord's responsibility to fix, and you may reduce rent
- If mold results from tenant behaviour, insufficient ventilation and heating causing condensation, it can be the tenant's responsibility
So the same patch of mold can be the landlord's problem or yours, depending on why it appeared. A leak or a cold, poorly insulated wall is the building's fault; condensation from a tenant who never airs the flat and keeps it cold is the tenant's. Often the cause is genuinely disputed, the landlord blames your ventilation, you blame the insulation, which is exactly why the next section (your duties) and documentation matter so much.
So when mold appears, the key question is what caused it, and that determines who pays and whether you can reduce rent. Because this is so often contested, you protect yourself by documenting the conditions (where the mold is, signs of structural causes like cold spots or leaks) and your own ventilation habits. (Mold damaging your belongings may also touch your contents insurance.)
Your duty to ventilate and heat
Here is the responsibility side that tenants must take seriously: you have a duty to ventilate and heat the flat reasonably to prevent condensation-related mold.
What this means in practice:
- Air rooms regularly, typically Stoßlüften (brief, full-window airing, opening windows wide for a few minutes several times a day rather than tilting them constantly)
- Keep adequate heating, a flat kept too cold encourages condensation on cold surfaces
Why it matters: if you neglect this and mold results, the landlord can argue it is your fault, and you lose the right to reduce rent (and might even be liable for the damage). German homes, especially older, airtight ones, genuinely need this active ventilation, the Stoßlüften habit is a real part of living here, not a landlord's excuse.
So ventilate and heat sensibly, and, importantly, document that you do. If a mold dispute arises, being able to show you aired and heated the flat properly protects your position, shifting the cause back toward structural faults rather than your behaviour. Keeping rooms reasonably warm and doing regular Stoßlüften is both genuinely effective at preventing mold and your evidence that any mold is not your doing. (Heating and ventilation tie into your utility setup too.)
When the landlord won't fix things
The hardest case: a real defect (the landlord's responsibility), and a landlord who won't act. The correct response, in order:
- Report the defect in writing, email or letter, and keep proof (a verbal mention is not enough; you need a record)
- Set a reasonable deadline to fix it
- Document everything, photos, dates, the defect's progression, and your reports
- If the landlord still does not act, escalate: rent reduction (done correctly), getting a tenant association (Mieterverein) involved, and in serious cases legal steps
The golden rule: report and document properly first, and never just withhold rent without following the process. The biggest tenant mistake is to stop paying out of frustration, which hands the landlord grounds against you. Instead, build a clear paper trail (written report, deadline, photos), then use the proper tools.
On the amount of any rent reduction: it must be proportionate to how much the defect impairs the flat, not arbitrary, and the rules are specific. Withholding too much, or without proper process, can put you in breach. Because getting both the amount and the procedure right is genuinely tricky, the smart move is to consult a tenant association (Mieterverein) before reducing rent. For a modest membership, they tell you whether your reduction is justified, how much is defensible, and how to do it safely, and they back you against an unresponsive landlord. This is the same resource that helps with deposit and condition disputes.
The bottom line: German law strongly protects tenants on mold and repairs. A serious defect lets you reduce rent (Mietminderung) proportionately, but only after reporting it properly, never just stop paying. Mold fault turns on the cause: structural is the landlord's, condensation from poor ventilation can be yours, so do your Stoßlüften and heat sensibly, and document it. If the landlord won't fix things, report in writing, set a deadline, document everything, and lean on a Mieterverein. Used correctly, your rights are real and effective.
What to do this week
- If your flat has a serious defect (mold, broken heating, water damage), report it to the landlord in writing with photos and a reasonable deadline, keeping proof, never just stop paying.
- Ventilate (Stoßlüften, brief full-window airing) and heat the flat sensibly to prevent condensation mold, and document that you do, to protect your position in any dispute.
- Before reducing rent (Mietminderung), consult a tenant association (Mieterverein) to get the amount and procedure right, since doing it wrong can put you in breach.
