Mold in Your Apartment: Who Is Liable + Up to 100 % Rent Reduction
Black Spots on the Wall — Now What?
It usually starts small: a few dark dots in the corner behind the wardrobe. Then it spreads. First the window seal in the bedroom, then the bathroom ceiling. Mold in a rental apartment isn't just disgusting — it can make you sick. And that's exactly why your rights as a tenant are particularly strong here.
Why Mold Is a Rental Defect
Section 536 BGB states: the apartment must be in a condition that allows normal use. Mold compromises that use — both in terms of health and practicality. German courts consistently recognize mold as a significant defect that entitles tenants to rent reduction.
This applies regardless of whether the mold is caused by structural issues or tenant behavior. What matters first is simply: the defect exists.
The Big Question: Who's to Blame?
This is where it almost always gets complicated in practice. The landlord says: "You don't ventilate properly." You say: "The walls aren't insulated." Both might be right — but who has to prove it?
The case law is clear: The landlord must first prove that the building structure is sound (BGH, judgment of 01.03.2000 — XII ZR 272/97). Only after that does the burden of proof shift to you — then you need to show that your ventilation habits were adequate.
In practice, this means: without an expert report, the landlord rarely gets far. And an expert report costs money — which the landlord must initially bear if they dispute the defect.
How Much Can You Reduce Your Rent?
The amount depends on severity. Some reference points from court rulings:
| Situation | Reduction | Source |
|---|---|---|
| Mold in one room, limited area | 5–10% | AG Hamburg, 22.04.2014 |
| Multiple rooms affected | 15–20% | LG Berlin, 15.10.2010 — 65 S 136/10 |
| Large-scale infestation, health risk | 20–50% | LG Hannover, 26.09.2002 — 7 S 58/02 |
| Apartment practically uninhabitable | 80–100% | LG Hamburg, 31.01.2008 — 307 S 130/07 |
The reference amount is always the gross warm rent (cold rent + utilities).
Step by Step: What to Do
1. Document everything Photograph the mold with the date visible. Measure the affected area. Note when you first noticed it and how it has progressed.
2. Report to your landlord In writing, ideally by registered mail. Describe the mold, attach photos, and set a reasonable deadline for remediation — typically 2 to 4 weeks for mold. Important: Section 536c BGB requires you to report the defect without delay. If you wait months, you risk liability for additional damage.
3. Wait for the deadline Give your landlord a chance to fix the problem. Many landlords respond once they receive a proper defect notification.
4. Reduce the rent If the deadline passes without action or results, you can reduce your rent. Safest approach: transfer the reduced amount and note in the reference line "Mietminderung wegen Schimmelbefall seit [date]" (rent reduction due to mold since [date]).
5. In case of health risk: act immediately If the mold is extensive, looks black, or you're experiencing health issues (respiratory problems, allergies), don't wait weeks for a response. In this case, you have the right to terminate the lease without notice (§ 569(1) BGB), if the landlord fails to act despite a formal warning.
What Not to Do
- Paint over it: Cosmetic treatment doesn't eliminate mold. It comes back, and you've weakened your evidence.
- Reduce rent without reporting: The defect notification is mandatory. Reducing without it risks rent arrears.
- Reduce too much: When uncertain, reduce conservatively and state the reservation. Once you're two months behind on rent, the landlord can terminate without notice (§ 543(2) No. 3 BGB).
Mold and Health
Mold releases spores that are inhaled through the air. Prolonged exposure can cause:
- Respiratory diseases and chronic coughing
- Allergic reactions (rhinitis, asthma)
- Headaches and fatigue
- In immunocompromised individuals: severe infections
If you notice health symptoms that started after the mold appeared, document them and see a doctor. A medical certificate significantly strengthens your position — including for a potential damages claim.
When to Get Help
Your local Mieterverein (tenant association) offers unlimited advice for €60–90/year. Alternatively: a specialist rental law attorney (initial consultation €50–150). For large-scale infestations, an independent expert report can also make sense — costing €300–800 depending on scope, but worthwhile if the landlord disputes the defect.
And before spending any money: try MieterHelfer.
Why MieterHelfer Helps with Mold Problems
Describe your situation — "mold in the bedroom for three weeks, landlord not responding" — and get an immediate assessment. MieterHelfer knows the current case law, explains your options, and tells you what rent reduction is realistic and what steps to take next.
Free, no registration, instantly available. Not a lawyer replacement — but the right first step when the black spots are growing.