Schimmel (Mould) in a Rented Flat: Your Rights (2026)

What does Schimmel mean in German tenancy law?

Schimmel (mould) in the flat is, in German tenancy law, a Mangel (defect) — a condition that impairs the agreed use of the dwelling. As soon as the infestation is more than insignificant, the rent is reduced by force of law for the duration of the defect (§ 536 BGB). This applies in principle regardless of whether the landlord is at fault — unless you caused the Schimmel yourself (for example through demonstrably incorrect ventilating and heating).

One thing up front, in this order: report first, then reduce. The Mietminderung (rent reduction) takes effect automatically, but it only becomes enforceable if you reported the Schimmel to the landlord in time and provably.

This page is the Schimmel-specific deep dive. The general rules on Mietminderung — Vorbehalt, the rate, forfeiture — are in the guide Mietminderung for defects.

First: send the Mängelanzeige (§ 536c BGB)

Under § 536c BGB you must report the Schimmel to the landlord without delay and give him the chance for Mängelbeseitigung (remedying the defect). Under § 535 Abs. 1 BGB the landlord owes you a flat in usable condition and must remove the Schimmel.

Always make the Mängelanzeige in writing and in a way you can prove: describe exactly which rooms are affected, attach dated photos, and set a reasonable deadline to fix it. The date of the notice is also the point from which your reduction is cleanly documented if there is a dispute.

Important: Report the Schimmel at once and in writing. A tenant who reports the defect too late can lose the reduction right and may even owe Schadensersatz (damages) for consequential harm (§ 536c Abs. 2 BGB). And do not cut the rent on your own by too much: until the amount and the cause are settled, keep paying the full rent under Vorbehalt. Reduce too much and fall into payment arrears, and you risk a Kündigung (termination, § 543 BGB).

Who has to prove who is at fault? (Beweislast)

With Schimmel this is the decisive question — and the Beweislast (burden of proof) is split (settled BGH case law):

• You prove that the Mangel exists — that there is mould and where. Photos and, if needed, an expert report do this.
• The landlord proves first that the cause does not lie in his sphere — e.g. that there are no thermal bridges, building defects or moisture in the fabric (BGH, VIII ZR 271/17). If there are indications of a structural cause, he must exonerate himself first.
• Only then must you prove you heated and ventilated correctly — i.e. that the Schimmel does not come from your behaviour.

In practice this means: you do not have to prove from the outset that you are not at fault. As long as the cause is unresolved, your reduction right stands. It is lost only once it is established that you caused the Schimmel.

Step by step

1. Document — dated photos of every affected area, notes on smell, extent and since when.
2. Send the Mängelanzeige — in writing to the landlord, with a description, photos and a reasonable deadline for Mängelbeseitigung (§ 536c, § 535 BGB).
3. Estimate the rate — anchor it to comparable rulings, not to a number you hope for (§ 536 BGB).
4. Pay under Vorbehalt — keep paying the full rent and state in writing that you reclaim the reduced portion.
5. Settle once it is fixed — the reduction applies only to the period the Schimmel existed; after that the full rent is due again.

What Minderungsquote is typical for Schimmel?

There is no statutory table. The rate depends on the severity, extent and location of the infestation and is decided case by case by the court (§ 536 BGB). The figures below come from published court decisions and are only reference points — they can vary considerably by court, region and the individual case.

Severity of the Schimmel	Court-typical rate*
Small mould spots, one secondary room (e.g. spots in the bathroom)	approx. 5 %
Mould in one living room, limited	approx. 10–15 %
Mould in several rooms (e.g. bathroom and bedroom)	approx. 20–30 %
Massive infestation in several rooms, musty smell	approx. 50–80 %
Flat uninhabitable / health-endangering	up to 100 %

*Reference points from case law, not a guarantee. Every case is judged individually — when in doubt, have it checked by a lawyer or a Mieterverein (tenants' association).

Common mistakes

• Reducing first, reporting later — without a timely Mängelanzeige (§ 536c BGB) the reduction is open to challenge, and you risk owing Schadensersatz.
• Reducing without Vorbehalt — payment arrears and Kündigung risk (§ 543 BGB).
• Setting the rate too high — reduce more than is justified and you pay the difference and fall into arrears.
• Causing the Schimmel yourself — for demonstrably wrong ventilating and heating there is no reduction; you may even have to remove the damage yourself.
• Not documenting — without photos, dates and a copy of the notice you can prove nothing in a dispute.

With HausMaus it's simpler

HausMaus has a free Mietminderung calculator: you select "Schimmel" as the Mangel, and the app estimates a Minderungsquote anchored to case law for your rent (§ 536 BGB). You can document the Schimmel with dated photos directly in the app — which creates a dated record — and HausMaus turns it into the matching Mängelanzeige to the landlord, including the deadline to fix it and the reminder to pay under Vorbehalt. For tenants this is free.

See pricing – 1 % of collected rent, free for tenants →