Broken heating, mould, noise: your right to reduce the rent

If your rental flat has a serious defect—whether it is broken heating, mould, noise, or water damage—German law gives you the right to reduce your rent automatically, without needing a court's permission. But this right only kicks in if you notify your landlord in writing immediately. Reducing rent without proper notice, or by too large an amount, carries real risks: your landlord can terminate your lease for non-payment of rent, and you could end up in an expensive legal dispute.

Step One: Send a Written Mängelanzeige (Defect Notification)

The moment you discover a defect in your flat, you must report it to your landlord in writing. This written report is called a Mängelanzeige. Without this notice, you lose your right to reduce rent—even if the defect is serious and lasts for months. Do not rely on phone calls, WhatsApp, or emails that could disappear into a spam folder. Instead, send a letter with tracking (Einschreiben mit Rückschein) or deliver it in person and keep a receipt.

Your Mängelanzeige should include a clear description of the defect, the date you discovered it, photos if possible, and a reasonable deadline for the landlord to fix the problem. For urgent issues like heating failure in winter or severe mould, a deadline of a few days is appropriate. For less critical problems, one to two weeks is standard. Be as specific as you can: instead of 'the flat is cold,' write 'the radiator in the bedroom is not working and the temperature is 15 degrees Celsius.'

How Much Can You Reduce the Rent?

German courts do not have a fixed formula for rent reduction. Instead, judges decide case by case, based on how severely the defect affects your ability to use the flat as agreed. This is the critical danger zone for many tenants: reducing too much can trigger eviction for non-payment, while reducing too little may not give you fair compensation.

Typical court-accepted ranges

Court decisions reveal rough patterns. For a complete heating failure in winter, courts have awarded reductions of 20–30% when indoor temperature drops to around 18 degrees Celsius. If temperatures fall below 15 degrees Celsius, where the flat becomes genuinely unusable, reductions can reach 50–100%. One Berlin court awarded a 10% monthly reduction for widespread mould across multiple rooms, including bedrooms and kitchen.

For significant mould damage that affects several rooms and requires regular cleaning, courts typically allow 10–20% reduction. However, if the landlord can prove the mould is your fault—because you failed to ventilate properly or maintain adequate heating—the reduction may be denied entirely. Persistent noise from neighbours or nearby construction, or water damage affecting usability, may justify 5–50% depending on severity. Minor defects affecting only one room or easily repaired issues typically justify less than 10%.

The Safer Route: Pay Under Reservation (Unter Vorbehalt)

If you are uncertain whether the defect justifies a rent reduction, or unsure of the right percentage, German law offers a safer path: payment under reservation. Instead of reducing the rent yourself, you continue paying the full rent but inform your landlord in writing that the payment is made 'under reservation' (unter Vorbehalt) due to an existing defect.

This approach protects you from eviction for non-payment, because you are paying the full amount due. At the same time, you preserve your right to claim a refund later—either through negotiation with the landlord or by winning it in court—once the defect has been legally assessed. If a court later rules that you are entitled to a 15% reduction for a three-month period, you can demand a refund of the overpaid rent going back to the date of your original notification.

Payment under reservation works best when a repair deadline passes without action, or when the repair is attempted but fails. Write to your landlord: 'I am paying the rent in full, but under the reservation that it is due to the defect of [describe defect]. I reserve the right to claim a reduction or refund once this matter is resolved.' Keep copies of all correspondence.

Special Case: Mould

Mould (Schimmel) receives special treatment in German law. Normally, the tenant must prove that a defect is the landlord's responsibility. With mould, the burden of proof flips: the landlord must prove that the mould is your fault, caused by improper heating and ventilation behaviour. If the landlord simply claims you did not air the flat enough, that argument alone will not succeed in court unless backed by evidence.

However, landlords can gather expert reports showing interior temperatures and moisture levels. If an engineer confirms that you failed to maintain minimum temperatures (usually 17–18 degrees Celsius) or refused to ventilate, the court may find you partly or wholly responsible. Courts currently expect tenants to ventilate briefly three to four times per day; demanding more than six ventilation sessions daily is considered unreasonable and cannot be imposed on you.

Documentation and Evidence

Before asserting any rent reduction, gather evidence. Take dated photos and videos of the defect. For heating issues, photograph the thermometer reading on different days and in different rooms. For mould, photograph affected walls, windows, and any condensation. Keep a log of your attempts to contact the landlord (phone calls, emails, texts), dates when you noted the problem, and any receipts for temporary fixes or cleaning supplies.

Save all letters and emails from your landlord. If you pay rent by bank transfer, the bank statement serves as proof of payment. If paying under reservation, always include the reservation clause in the transfer note or a separate letter. Document temperatures with a thermometer or hygrometer (humidity meter, available cheaply online). This evidence will be crucial if a dispute goes to court.

Getting Legal Advice: The Mieterverein Route

Before reducing rent unilaterally, membership in a Mieterverein (tenant association) is your best investment. Membership typically costs between 50 and 100 euros per year, including a small joining fee. In return, you gain access to free legal consultation on all rental matters, including whether your case justifies a reduction and by how much. Many local Mietervereine will even draft a formal letter to your landlord on your behalf.

All 16 German states have local Mietervereine that belong to the national Deutscher Mieterbund (German Tenants' Association). You can find your nearest branch by postcode at mieterbund.de. Once you join, there is typically a three-month waiting period before the association will handle a brand new dispute, so join early, ideally when you move in. If you already have an active legal case, you cannot join and receive immediate support for that specific issue—so proactive membership is the smarter choice.

Advice from a Mieterverein is conducted primarily in German, but larger city offices (Berlin, Munich, Frankfurt) often have English-speaking advisors or allow you to bring a translator. The cost of private legal consultation on rental disputes easily exceeds 250 euros per hour, so the annual membership fee quickly pays for itself.

The Risk of Going It Alone

If you reduce rent without proper notice to the landlord, or by an amount a court later deems excessive, your landlord can file a formal eviction notice (Kündigung) for non-payment of rent. German law allows eviction if rent is unpaid for two consecutive months. Even if you later win in court and are owed a refund, the eviction process has already begun and will be expensive and stressful to defend.

Additionally, some leases contain a 'Kleine Reparaturen' clause (small repairs clause) that shifts responsibility for minor repairs to you, up to a cap (often around 120 euros per year). If a defect falls within this cap and the contract explicitly assigns it to you, you may not be entitled to a rent reduction at all. A lawyer or Mieterverein can review your contract and advise whether such a clause is valid and applicable.

If the Landlord Does Not Respond

If the landlord ignores your Mängelanzeige and does not repair the defect within the deadline you set, you have options. You can issue a second, more formal notice (often written by a Mieterverein or lawyer) giving a final deadline. If still ignored, you may hire a tradesperson to do the repair yourself and demand the landlord reimburse you. You can also file a small claim in the local court (Amtsgericht) requesting a refund of rent or a court-ordered reduction retroactive to the date of your original notification.

Some tenants also consider withholding rent entirely after a defect goes unrepaired for an extended period, but this is riskier than paying under reservation and should only be pursued with legal advice. Again, the safest path is to keep paying, document everything, and pursue a refund claim with the support of a Mieterverein or lawyer.

Key Takeaway

German tenancy law does protect you from living in a defective flat. But exercising that protection requires care: notify the landlord immediately in writing, document the problem thoroughly, and either consult a Mieterverein before reducing rent unilaterally, or use the safer 'payment under reservation' method while you gather evidence and seek advice. This methodical approach maximises your legal protection and minimises the risk of eviction or lengthy court battles.