Mold in the Apartment: Who Pays, and What Should Tenants Do First?

Why mold is suddenly a big topic again

Many tenants first notice it on a cold morning: a faint musty smell, a dark shadow in the corner behind the wardrobe, or small black dots around the window reveal. Mold is not a new problem—but it is getting more attention right now, for very everyday reasons.

Buildings are being insulated more tightly to save energy, windows seal better than older models, and people try to heat less to reduce costs. That combination can reduce air exchange indoors. At the same time, humidity sources haven’t changed: showers, cooking pasta, drying laundry inside, even breathing at night. When moist air meets cold surfaces (outer walls, corners, window frames), condensation can form—and mold loves that.

What makes mold so stressful in a tenancy is that it is both a health concern and a money question. Tenants wonder: “Is this my fault because I didn’t air the room enough?” Landlords ask: “Is this a usage issue rather than a defect?” And in the middle there is the practical problem: the stains often grow while both sides argue.

To make this concrete, imagine a typical scenario: You move into a renovated apartment with new windows. In winter, you lower the heating to save money. Two months later you spot mold behind a large cabinet placed against an outer wall. The landlord says: “You must ventilate more.” You say: “The wall feels icy cold; this can’t be normal.” Both might be partly right—or one side might be clearly responsible. The key is how you react from day one, because your next steps can influence who pays and whether you can reduce rent.

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First response checklist: what to do (and what not to do)

The first days after discovering mold matter. Not because a court case is around the corner, but because evidence disappears quickly and misunderstandings grow. Also, mold is not just a cosmetic issue—depending on the extent, it can affect health and furniture.

1) Document like you’d want to convince a stranger. Take photos in good light, from different distances (close-up and wide shot), and include a reference point (e.g., a ruler or coin). If possible, photograph the spot over several days to show whether it spreads. Make a short note: date, room, wall side (outer wall / inner wall), and what was nearby (wardrobe, bed, curtains).

2) Notify the landlord in writing—early. A quick phone call is fine as an extra, but it should not replace written notice. Use email or letter and keep proof (sent email, registered letter, or at least a witness for posting). Describe the location and size, attach photos, and ask for inspection and remediation.

3) Don’t “solve” it in a way that destroys evidence. Wiping a small spot for hygiene is understandable. But repainting the wall, applying anti-mold paint, or having someone remove wallpaper can make it harder to clarify the cause. If you must clean a small area for health reasons, photograph it first and note exactly what you did.

4) Reduce humidity drivers where possible. You don’t have to live like a lab technician, but practical steps help: lid on pots, use bathroom fan if present, keep furniture a small distance from cold outer walls, and avoid drying laundry in unventilated rooms. These steps are also useful later if someone claims the problem is purely “tenant behavior.”

• Quick sanity check: Is the mold on an outer wall/corner? Around windows? Behind furniture? Or in the bathroom with no window?
• Look for warning signs: Cold wall surfaces, persistent condensation on windows, peeling wallpaper, salty stains (possible moisture intrusion).
• Think “pattern”: One small corner can be ventilation-related; widespread patches or recurring dampness can indicate a defect.

5) Set a reasonable deadline for action. If you report mold, you can request that the landlord takes steps to inspect and fix it. In everyday practice, a deadline of around 10–14 days is often used for a first reaction/inspection, but the “right” timeframe depends on severity. Heavy mold or health risk calls for faster action.

6) Consider measuring humidity—carefully. A cheap hygrometer can help you understand what’s happening. If indoor humidity is permanently high (for example often above ~60%), it supports the idea that ventilation/heating adjustments are needed. But don’t treat it like a magic legal weapon: single readings without context rarely prove fault. Still, a small log can help clarify your routine if the dispute escalates.

Who pays for what: typical cost questions (and what decides them)

When people ask “Who pays?”, they often mean several different things at once: Who pays for removal? Who pays for a professional assessment? Who pays for damaged furniture? Can the tenant reduce rent? The answer depends heavily on cause and process (especially notice and documentation).

In many tenancy systems (including the typical approach in Germany), the landlord is responsible for providing and maintaining an apartment that is fit for living. If mold results from a defect in the building fabric—like water ingress, a leaking pipe, insufficient insulation causing severe thermal bridges, or construction flaws—then remediation is typically the landlord’s job.

On the other hand, if mold is mainly caused by the tenant’s behavior—like consistently not heating at all in winter, never ventilating, drying laundry daily in a small room with closed windows, or blocking air circulation with huge furniture pressed against cold walls—then the tenant can be held responsible for damage and costs.

The difficult reality: many cases are mixed. For example, a poorly insulated corner (landlord issue) combined with a wardrobe placed flush against the wall and low heating (tenant contribution). In such situations, disputes often turn into questions of evidence and reasonableness: How much ventilation is “normal”? Is the apartment designed so that normal living creates excessive humidity? Did the tenant receive instructions about ventilation after new windows were installed?

Rent reduction: If mold significantly restricts use of the apartment (for example, you can’t use a room, or there is strong odor or health concern), tenants often consider reducing rent. But the “how much” is not a DIY number you pick from frustration. It depends on severity and on whether the defect is properly reported. A common mistake is reducing rent without clear written notice of the defect and without giving the landlord a chance to remedy it.

Hotel / alternative accommodation: In extreme cases (major mold, uninhabitable rooms), tenants ask whether the landlord must cover alternative accommodation. This typically hinges on whether the apartment is genuinely unfit for living and whether the landlord is responsible for the cause. Practical tip: if you think it’s unsafe, get a professional medical or technical opinion rather than relying on assumptions.

Furniture and personal items: Mold can destroy wardrobes, mattresses, clothes. Whether you can claim compensation depends again on fault and causation. If the mold stems from a building defect, claims are more plausible. If the mold is linked to how items were stored (e.g., tightly against a cold wall with no airflow), the discussion changes. In any event: photograph damaged items, keep receipts if available, and don’t throw everything away before documenting.

Professional assessment (“expert”): When both sides disagree about the cause, an expert assessment can clarify. Who pays can become a dispute itself. In many real-life cases, parties try a step-by-step approach first: landlord inspection → remediation attempt → if dispute persists, then expert. Tenants should be cautious about commissioning expensive reports without coordination, because reimbursement is not guaranteed.

How to talk about mold without turning it into a fight

Mold discussions escalate quickly because they feel personal. Tenants feel accused of living “wrong.” Landlords feel blamed for “bad buildings.” A more effective approach is to keep communication practical and evidence-based—like troubleshooting a car issue instead of arguing about who is a bad driver.

Use neutral language. Instead of “Your building is defective,” try: “There is visible mold growth on the outer wall in the bedroom corner; photos attached. Please inspect and propose remediation.” This frames the issue as a shared problem to solve.

Offer cooperation without admitting fault. You can write: “We ventilate regularly (morning/evening) and heat the rooms. If you recommend a specific ventilation routine for the new windows, please provide it in writing.” That shows willingness and creates a paper trail.

Ask for concrete steps. A helpful request is not “Fix it,” but “Please arrange an inspection, check for moisture sources (leaks, thermal bridges), and advise on necessary measures.” If the landlord later claims you prevented access, you want a record that you asked for an appointment and were available.

Keep a simple ‘mold diary’ for two weeks. This is not about living under surveillance; it’s about clarity. Note ventilation times, heating level, indoor humidity (if measured), and any changes. If the landlord insists the mold must be your behavior, a diary can counter vague accusations.

Real-life mini scenario: A tenant discovers mold behind a sofa on an outer wall. They take photos, pull the sofa 8–10 cm away, ventilate twice daily, and measure humidity. The mold returns within weeks and the wall remains unusually cold. The landlord then arranges an inspection and discovers a thermal bridge at the wall junction. The tenant’s early documentation helps show the problem persisted despite reasonable behavior.

Another scenario: Mold appears only in the bathroom; the fan is broken and the window handle is defective. The tenant reported both issues months earlier. Here, the paper trail matters: it shows the tenant raised the issue and the landlord didn’t repair ventilation-related defects, which strengthens the tenant’s position.

Common mistakes that backfire:

• Waiting too long because you hope it goes away—mold rarely does.
• Only calling and never sending written notice—later there is “no record.”
• Reducing rent impulsively without correct procedure or documentation.
• Covering it with paint and then trying to argue about the cause.

Practical wording you can adapt (example):
“On 02/11/2026 we discovered mold growth on the bedroom outer wall (corner near the window), approx. 30 x 20 cm. Photos attached. We request inspection and remediation. Please propose an appointment within 10 days. We ventilate regularly; if you recommend specific measures, please let us know in writing.”

This keeps the message factual, time-stamped, and solution-oriented—exactly what you want if the case later needs clearer evaluation.