Complaining About Building Defects: Report Defects Correctly and Secure Your Rights
Cracks, damp basements, crooked windows – hardly any build stays entirely defect-free. Your reaction is decisive. This guide shows the concrete procedure in a defect case in 2026: a formally correct defect notice, an appropriate deadline, right of retention, securing of evidence and the use of surveyors – step by step and legally sound.
Cracks in the plaster, damp basement walls, crookedly fitted windows, a ventilation system on strike – hardly any building project remains entirely free of defects. What is decisive is not the occurrence of a defect but your response to it: anyone who complains in the correct form, sets deadlines and secures evidence safeguards their rights and forces the construction company to remedy the defect. Anyone who, by contrast, only raises the defect verbally or hesitates too long often ends up stuck with the repair costs. This guide takes you step by step through the correct approach in the event of a defect – legally secure and practical.
When a building defect exists – and what rights you then have
Short answer: A building defect exists as soon as the structure deviates from the contractually agreed or the customary, expected condition (§ 633 BGB). The spectrum ranges from a cosmetic blemish (a scratch in the parquet) through functional faults (leaky windows) to a serious building defect (a damp basement, structural problems). Within the five-year warranty period, you are entitled to five rights under § 634 BGB: subsequent performance (rectification), self-remedy with reimbursement of costs, reduction of the payment, withdrawal from the contract and damages. The first and most important step is always the correctly formulated notice of defects (Mängelrüge) with a deadline for subsequent performance.
Of central importance is the point in time of the building acceptance (Bauabnahme): before acceptance, the construction company must prove that its work is free of defects – after it, the burden of proof reverses and you must prove the defect. That is why every recognisable defect belongs in the acceptance protocol. How acceptance takes effect legally and which deadlines depend on it can be read in detail in the guide to building acceptance & warranty. This guide follows on from that and explains the concrete approach when a defect arises during the warranty period.
The builders’ rights regarding defects under the German Civil Code at a glance
| Right | When it makes sense | Prerequisite |
|---|---|---|
| Subsequent performance / rectification | always first | notice of defects + reasonable deadline |
| Self-remedy + reimbursement of costs | deadline elapsed without success | prior setting of a deadline |
| Reduction of the payment | defect remains / minor | deadline unsuccessful + payment outstanding |
| Damages | consequential damage occurred | fault of the construction company |
| Withdrawal from the contract | serious, irreparable defect | significant defect + deadline |
How to formulate the notice of defects correctly
Short answer: In 2026, an effective notice of defects is made in writing, describes the defect as precisely and comprehensibly as possible (location, type, extent), expressly demands subsequent performance and sets a reasonable deadline for its remedy. You need neither know the cause nor propose a solution – it is enough to describe the defective appearance (the “symptom”). Send the notice verifiably by registered letter with acknowledgement of receipt or by e-mail with read receipt, and document its delivery. Only in this way can you later prove that and when you gave notice.
The most common mistake is the purely verbal complaint on the building site. It is hard to prove legally and often fizzles out without effect. Instead, describe every defect individually and concretely: not “the bathroom is defective”, but “in the upper-floor bathroom, the floor tile next to the washbasin has a 15 cm long crack and the tile splashback has chipped at the corner”. The more precise the description, the fewer ways the construction company has to dodge.
Why the symptom theory works in your favour
As a builder, you only have to describe the visible defect symptom – not its technical cause. So if you give notice that “mould keeps forming in the corner of the bedroom”, this notice automatically covers all conceivable causes (a thermal bridge, a leaky vapour barrier, faulty ventilation). The construction company must determine the cause and remedy the defect completely. This protects you from naming the wrong technical reason.
Setting a deadline: how much time the construction company must be given
Short answer: The deadline for subsequent performance must be “reasonable” – it is measured by the type and extent of the defect. For smaller works (readjusting a window, patching plaster) one to two weeks are often sufficient in 2026; for extensive measures (basement drying-out, screed replacement) three to six weeks are reasonable. Set the deadline with a specific calendar date (“by 15 March 2026”), not with vague wording. A deadline that is too short does not render the notice ineffective but automatically sets a reasonable deadline in motion. Only when the deadline elapses without success do your further rights, such as self-remedy or reduction, open up.
Always word the deadline in a binding way and announce the consequences: “Should you fail to remedy the defect by the stated date, I reserve the right to have the remedy carried out by a third-party company at your expense (self-remedy) and/or to reduce the payment accordingly.” This announcement increases the pressure and creates the legal basis for the next step. Important: if the company expressly and definitively refuses subsequent performance, the need to set a deadline lapses.
Avoiding defects starts with the choice of provider
The best notice of defects is the one you never have to write in the first place. Compare, free of charge, the fixed-price offers of vetted manufacturers from our network – with a clear building and service specification as well as documented build quality, you reduce the risk of defects from the outset.
Right of retention: using payment as a lever
Short answer: As long as a defect has not been remedied, you may retain part of the payment (§ 641 (3) BGB). In 2026, the law permits you to retain double the expected defect-remediation costs – in practice, two to three times the amount is often recognised. For a defect whose remedy costs €4,000, you can therefore hold back around €8,000 to €12,000 of the final instalment. The right of retention is your strongest lever, because no company likes to forgo money. Important: the amount retained must be in reasonable proportion to the defect, otherwise you yourself fall into default of payment.
Use the right of retention deliberately and document it in writing: inform the construction company which amount you are retaining for which specific defect and that you will pay it out promptly once subsequent performance is free of defects. In a consumer construction contract (Verbraucherbauvertrag), the security retention is also relevant: at the start of construction, the contractor must provide a completion guarantee of 5 % of the remuneration – you can also fall back on this in the event of defects. Keep both instruments in view to secure your position.
Securing evidence: with photos, protocols and experts
Short answer: After acceptance, you bear the burden of proof – which is why seamless documentation is decisive. Record every defect with dated photos and videos, a written description, a construction diary (Bautagebuch) and, if possible, with witnesses. For larger or contentious defects, you should call in an independent building surveyor (Bausachverständiger): their report (usually costing €500 to €2,500 in 2026) proves the cause, extent and remediation costs and is often decisive in court. For acute, worsening damage, you can additionally apply to the court for independent evidence proceedings, which record the condition in a legally secure manner.
- Document every defect with dated photos from several perspectives.
- Keep a construction diary: date, weather, companies present, any anomalies that arose.
- Archive all correspondence (notices, deadlines, replies) chronologically.
- Name witnesses who can confirm the defect and its reporting.
- For contentious defects, commission an independent building surveyor early.
- For progressing damage, consider independent evidence proceedings.
How to find a suitable surveyor and what a report costs is explained in the guide to prefab house surveyors. For the systematic recording of defects, our instructions for the defects inspection help.
The independent evidence proceedings
If a defect visibly worsens or evidence threatens to be lost (for example because construction continues), you can apply to the competent court for independent evidence proceedings (selbstständiges Beweisverfahren) under § 485 of the German Code of Civil Procedure (ZPO). A court-appointed surveyor then secures the condition neutrally and in a legally secure manner. The proceedings suspend the limitation period and are often cheaper than a later trial based on inaccurate recollections.
The most common building defects – and what matters with them
Short answer: Among the most common building defects in 2026 are: moisture in the basement and at the floor slab, cracks in plaster and masonry, thermal bridges and the mould that results from them, leaky window and door connections, defective sealing of bathrooms and balconies, faults in the vapour barrier in the roof area as well as sound insulation and screed defects. Many of these only come to light after months – so keep a careful eye on your house throughout the entire warranty period and give notice of every suspicion in good time, before the deadline expires.
Common building defects and their typical urgency
| Defect | Typical cause | Urgency |
|---|---|---|
| Damp basement | faulty sealing / tanking | very high |
| Mould in room corners | thermal bridge, ventilation concept | high (health) |
| Cracks in the plaster | settlement, drying, workmanship | check |
| Leaky windows | faulty connection / installation | high (energy) |
| Leaky bathroom / balcony | defective sealing | very high (consequential damage) |
| Screed / sound defects | workmanship error, impact sound | medium to high |
When in doubt, report a defect one time too many rather than too late: a notice of defects does not suspend the limitation period on its own – for that you need an acknowledgement by the company, evidence proceedings or a lawsuit. If the five-year period is nearing its end and a defect is still open, you should seek legal advice early. Technical terms relating to building law and construction execution are explained by the construction glossary.
How to proceed in five steps in the event of a defect
Short answer: In the event of a defect, in 2026 you are best advised to proceed in five steps: first, document the defect (photos, description, date); second, send the written notice of defects with a reasonable deadline verifiably; third, if necessary, engage a surveyor and use the right of retention; fourth, after the deadline has elapsed unsuccessfully, decide on self-remedy, reduction or damages; fifth, in serious or contentious cases, bring in a specialist lawyer for construction and architectural law. Calm and system pay off – anyone who proceeds in an orderly manner enforces their rights significantly more successfully.
- 1. Secure the defect: dated photos, precise description, construction diary.
- 2. Send the notice of defects in writing and verifiably with a specific deadline.
- 3. Use the right of retention and – in the event of a dispute – commission a surveyor.
- 4. After the deadline elapses unsuccessfully: self-remedy, reduction or damages.
- 5. For serious defects or an expiring deadline: bring in a specialist construction lawyer.
A solid basis of evidence is created long before the first defect – namely with a clear contract and a careful acceptance. So check your contract thoroughly (see the guide to checking the building contract) and never approach the acceptance under time pressure. In this way you give yourself the best starting position should rectification ever be required. How contract, acceptance and warranty interact across the entire process is summarised by the guide to buying a prefab house.
Build safely – with vetted manufacturers and a clear fixed price
You most effectively avoid a dispute over defects by relying from the outset on a reputable provider with a seamless service specification. We connect you free of charge with suitable manufacturers offering a fixed-price guarantee – for a building project that never becomes a matter of dispute in the first place.
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The most common price questions around Complaining About Building Defects – answered concisely by the Prefabricated House editorial team (as of 2026).
