Rent reduction for mould: what landlords should do when the tenant cuts the rent
Moe Afonso · 2026-10-13
Mould is the number one issue between landlords and tenants. For the tenant, it is a defect that restricts the use of the apartment and can endanger health. For the landlord, it is often the result of incorrect heating and ventilation (Heiz- und Lüftungsverhalten).
If the tenant reduces the rent, the landlord immediately loses liquidity. Here you will find out what the courts have decided, who has to prove the cause and how you as a landlord can correctly respond to a reduction.
01When a rent reduction for mould is justified
A rent reduction is only possible if the apartment has a "significant defect" (§ 536 BGB).
- Mould is a defect if it makes the use of the rooms more than insignificantly difficult or if there is a health risk.
- No reduction if the tenant is responsible for the mould, for example through insufficient ventilation or placing furniture too close to cold outer walls.
- No reduction if the defect was already known at the time of signing the contract (§ 542 BGB).
02Rent reduction table for mould (judgments)
There is no "official" table. Courts decide each individual case. These judgments serve as guidelines for landlords:
| Room / Case | Reduction | Judgment |
|---|---|---|
| Bedroom, mould over skirting boards | 15% | LG Berlin, 23/05/2014, 65 S 524/13 |
| Living room, several square metres | 20% | LG Dresden, 22/11/1994, 15 S 481/93 |
| Kitchen and bathroom, small spots | 5% | AG Schöneberg, 13/01/2009, 109 C 256/08 |
| Whole apartment, health risk | 100% | LG Berlin, 13/07/1990, 65 S 299/89 |
| Basement, slight dampness (old building) | 0% | LG Berlin, 26/03/2013, 63 S 621/12 |
03Who has to prove what? (Burden of proof)
The dispute usually revolves around the cause: Building defect or ventilation error? The Federal Court of Justice (BGH) has established a clear sequence for this (judgment XII ZR 272/97):
- Tenant: Must report the defect and prove that there is mould.
- Landlord: Must prove that the cause does not lie in their area of responsibility (e.g. leaking roof, thermal bridges, rising damp). They must prove that the building is "technically defect-free".
- Tenant: If the building is defect-free, the tenant must prove that they have ventilated and heated sufficiently.
04First steps for landlords when a tenant reports mould
- Immediate inspection: View the damage yourself or send the property management. Take photos.
- Duty to mitigate damage: As a landlord, you are obliged to keep the damage as small as possible. Even if you think the tenant is at fault, you should first have the mould removed.
- Mould protocol: Give the tenant a protocol to fill out (when did the mould appear? how is ventilation done?).
- Expert: In case of large damage or a persistent dispute, hire a certified expert for indoor mould. Their report is the basis for a court case.
05How to react to a rent reduction
If the tenant shortens the payment:
- Acceptance under reserve: If you are not sure, write to the tenant that you accept the reduction only under reserve. This allows you to claim the money back later if it turns out the tenant was at fault.
- Warning/Notice: If the tenant reduces the rent too much or unjustifiedly, and the arrears reach more than one month's rent, you can issue a warning. If the arrears reach two months' rent, a notice (Kündigung) is possible. Caution: This is risky if the court later decides the reduction was justified.
- Repair: The reduction ends as soon as the defect is removed. If you fix the mould, the full rent is due again from that day.
06Calculation of the reduction
The reduction is calculated from the gross rent (Bruttomiete), i.e. net cold rent plus all service charge advance payments (BGH XII ZR 225/03).
| Sarah's tenant reduces by 15% due to mould in the bedroom. | |
|---|---|
| # | Calculation |
| Net cold rent | €800 |
| Service charge advance payment | €200 |
| Gross rent | €1,000 |
| Reduction (15% of €1,000) | €150 |
| Rent to be paid | €850 |
For Sarah as a landlord, the loss of €150 affects the cold rent 1:1 because she still has to pay the service charges (heating, water, insurance) to the service providers.
07Risks for landlords
- Maintenance backlog: If you ignore mould, it can attack the building fabric and lead to much higher costs later.
- Lost rent: An unjustified reduction can often only be recovered through a court case.
- Notice by the tenant: In case of severe mould, the tenant can give notice without observation of a period (extraordinary notice).
08Read more
- Rights and obligations of landlords
- Property management: letting without stress
- Service charge settlement: what to check
- Extraordinary notice in the glossary
09Sources
All sources accessed on 13/10/2026.
- § 536 BGB (Rent reduction for material and legal defects)
- § 536c BGB (Duty of the tenant to report defects)
- BGH, judgment of 15/12/2010, VIII ZR 113/10 (Reduction basis is gross rent)
- BGH, judgment of 05/12/2018, VIII ZR 271/17 (Mould and thermal bridges in old buildings)
- BGH, judgment XII ZR 272/97 (Burden of proof for mould)
Note: This guide provides general information and does not replace legal advice. Each case of mould is individual and should be assessed locally.
FAQHäufige Fragen
Is there a binding rent reduction table for mould?
No. The law does not state percentages. Tables on the internet collect individual judgments that do not bind any other court. The rate always depends on the room, area, duration and health risk in the specific case.
How high is the rent reduction for mould in the bedroom?
The Regional Court (LG) of Berlin applied 15% for mould in the bedroom above the skirting boards (judgment of 23/05/2014, 65 S 524/13). This is a guideline, not a fixed value. For larger infestations or multiple rooms, courts have assumed higher rates.
Must the tenant announce the reduction beforehand?
The tenant must report the defect immediately, not the reduction. The rent is reduced by operation of law as soon as a defect exists. If the tenant fails to report it, they cannot reduce for the time you were unaware of it.
Who has to prove where the mould comes from?
Initially the landlord. They must show that the cause does not originate from their area, i.e. it is not due to the building. If successful, the tenant must prove that they have heated and ventilated sufficiently (BGH XII ZR 272/97).
Is mould in an old building always a defect?
No. Thermal bridges and a resulting risk of mould are not a defect if the house meets the standards of its time of construction and nothing else has been agreed (BGH VIII ZR 271/17). The tenant must then heat and ventilate reasonably. If mould still occurs, it again depends on the cause in the individual case.
Can I give notice if the tenant reduces too much due to mould?
Under certain circumstances, yes, if the arrears reach the legal limit and the reduction was unjustified (BGH VIII ZR 138/11). The tenant can, however, make the notice ineffective by paying within the grace period. Have the individual case checked by a lawyer beforehand.
Is the reduction calculated from the cold or warm rent?
From the gross rent (Bruttomiete), i.e. cold rent plus advance payment of service charges (BGH XII ZR 225/03). For landlords, it nevertheless acts fully on the cold rent because the service charges continue.
Who pays for the mould removal?
If the cause lies with the building, the landlord; for condominiums with the cause in the common property, the association (WEG). If the tenant caused the mould through their behaviour, the landlord can claim damages.