Mold in a shared flat quickly leads to disputes, and it is often unclear who caused the problem and who has to fix it. For tenants in Germany, the general rules of the German Civil Code (Bürgerliches Gesetzbuch, BGB) apply, above all on defects in the rented property (Mängel) and the duty to report them. This guide explains when mold counts as a defect, what you must report, what you can do yourself and where the limits lie.
Short answer: Mold counts as a defect in the rented property if it removes or reduces the flat’s fitness for use. Under § 536c para. 1 BGB you must report it to the landlord without undue delay. Whether and how much you may reduce the rent depends on the extent and the cause and is decided case by case if there is a dispute. Last updated: November 2026.
The most important points at a glance
- Mold is a defect of the rented property if it removes or reduces the flat’s fitness for use (§ 536 para. 1 BGB).
- You must report the defect to the landlord without undue delay (§ 536c para. 1 BGB).
- For the period of impairment you only owe a reasonably reduced rent. The law does not set a fixed percentage.
- The cause plays a role in deciding who pays for the repair. Whether a structural problem or user behaviour predominates is examined case by case.
- Documenting the mold, the date and its extent gives you the better position in a dispute.
- If you are unsure, a local tenants’ advice service can help before you reduce the rent.
When does mold in a flat count as a defect?
Under § 536 para. 1 sentence 1 BGB, the tenant is released from paying rent if the rented property has a defect that removes its fitness for use, or if such a defect arises during the tenancy. For the period in which fitness is only reduced, sentence 2 requires the tenant to pay only a reasonably reduced rent.
Whether mold impairs a flat only slightly or considerably cannot be judged in general terms. What matters is the size of the affected area, its location, for example in a bathroom, on an outside wall or at a window reveal, and whether furniture, laundry or your health are affected.
| Typical situation | Classification | What you should check |
|---|---|---|
| Small spot at a window reveal | Often a sign of construction or ventilation problems, case by case | Photograph location and size and note the date |
| Extensive mold on an outside wall | Can be a defect that noticeably affects use | Inform the landlord promptly in writing |
| Mold in the bathroom after lasting dampness | Clarify the cause: building fabric, ventilation or heating habits | Document your ventilation and heating habits |
Do you have to report the mold immediately?
Yes. As soon as you notice the mold, you must report it to the landlord. Under § 536c para. 1 BGB the tenant must report a defect without undue delay, meaning without culpable hesitation, not only after several weeks. The law does not prescribe a particular form for this.
Even so, a message in text form is advisable, for example by email or by letter with a copy, so that you can prove when the landlord received it. If you wait a long time, the landlord may argue that the damage could have been prevented earlier. How much a delay matters is assessed by a court on the concrete facts.
What you should do as a tenant
- Photograph the mold with the date, note the locations and rough dimensions, and back up the photos several times.
- Report the findings in writing to the landlord or the property management and describe where and since when the mold appears.
- Ask for an inspection appointment and note in writing what was found.
- Ventilate and heat as the landlord or an expert recommends, and document this.
- Have larger work on walls or ceilings carried out only after agreement, so that your claims are not put at risk.
Which documents should you collect?
In a dispute, the better documentation often decides the outcome. Keep together the following items:
- The tenancy agreement and any attachments, such as the handover protocol.
- Photos with dates and a short timeline of when you noticed what.
- All letters and emails to the landlord or the property management, including their replies.
- Receipts for additional costs, for example for drying equipment or cleaning of clothes.
- A medical certificate if health complaints occur.
If you signed the tenancy agreement together with flatmates, inform them about the findings. Still send the report to the landlord in writing, so that receipt is clear.
Can you reduce the rent?
The reduction of rent is the legal consequence described in § 536 para. 1 sentence 2 BGB. The law does not set a fixed percentage. The amount depends on how far the use is affected and is determined case by case if there is a dispute. If you reduce the rent, explain the reduction in writing beforehand, because a reduction that is too high can be treated as arrears.
Worked example (assumption): The rent for the flat is 400 euros per month, and the impairment justifies a reduction of 10 percent in this case. The rent payable for that period would then be 360 euros. The figure only illustrates the calculation and says nothing about what applies in your case.
Who pays for the damage and the repair?
Responsibility depends on the cause. If it lies in the building fabric, for example in leaking windows or missing insulation, the repair is in principle the landlord’s responsibility. If user behaviour contributed to the mold, part of the cost may fall on the tenant.
Allocating responsibility is often difficult. A joint inspection with everyone involved or an independent expert report that records cause and extent can help.
Frequently asked questions
Can the landlord terminate my tenancy because of mold?
A termination because of a defect is not automatically permitted. Whether a ground for termination exists depends on the cause and on the conduct of both sides. If you receive a termination letter, have it checked promptly, because deadlines run from receipt.
Do I have to keep paying rent while the mold is there?
You only owe the full rent as long as the flat can be used fully. For the period of impairment, a reasonably reduced rent may be due (§ 536 para. 1 sentence 2 BGB). Do not simply keep paying in full. Clarify the amount in writing instead.
Do I have to ventilate myself to prevent mold?
Anyone using a flat should ventilate and heat it so that lasting moisture does not build up. Whether the conduct in a specific case was faulty is examined case by case. An expert report can clarify whether structural causes predominate.
What if the landlord does not respond?
Set a reasonable deadline for remedying the defect in writing. If the landlord still does not react, a tenants’ advice service or a lawyer can clarify the next steps. If you have health complaints, a medical record is important.
Where can I find the exact wording of the law?
The sections are freely available on gesetze-im-internet.de, the official portal of the German federal government for federal laws. There you will find the current wording of the German Civil Code that this guide refers to.
What to do now
- Photograph the mold, note the date and location, and back up the photos.
- Report the defect in writing and without undue delay to the landlord or the property management.
- Agree in writing which amount you pay until the repair, and explain any reduction clearly.
- Get advice before you stop payments or commission work yourself.
Related reading
- Wohnen im Studium: Miete, WG, Wohnheim und Wohngeld im Überblick
- Student Tenancy Agreement: What You Should Check Before Signing
- How to Find a Shared Flat: Tips for a Successful Search
- Student Dorm or Shared Flat: Which Suits You Better?
Sources: § 536 BGB: Mietminderung bei Sach- und Rechtsmängeln (Reduction of rent for defects), gesetze-im-internet.de, accessed November 2026 and § 536c BGB: Anzeige von Mängeln (Notification of defects), gesetze-im-internet.de, accessed November 2026. German legal text, English summary.
Last updated: November 2026. This guide is general information, not individual advice.
