Expertise & Advice
An overview of mold, moisture, and building physics
In this section, we share our knowledge about moisture, mold, and structural damage.
The content is based on the daily assessment practice of certified expert Michael Trübswetter and takes into account the requirements of DIN standards, the German Federal Environment Agency (UBA), and the WHO.
The aim is to provide owners, managers, and specialist companies with clear information on identifying the causes of typical building damage, assessing it, and repairing it.
Mold & Interior Hygiene
Mold develops when moisture comes into contact with organic materials—such as wallpaper, plaster, wood, or dust—over a prolonged period of time.
The causes are often thermal bridges, inadequate ventilation, construction defects, leaks, or water damage.
Condensation on cold wall surfaces or in poorly ventilated areas creates ideal conditions for mold growth.
Yes. Mold can cause allergies, respiratory irritation, asthma, or headaches.
According to the UBA and WHO, all visible mold should be removed professionally, regardless of the type.
There is no such thing as a “safe” amount of mold.
Children, allergy sufferers, and people with weakened immune systems are particularly at risk.
For more information on health, please visit: WHO Guidelines on Mold and Moisture
According to the guidelines issued by the Federal Environment Agency, a distinction is made between three categories of damage:
- Category 1: minor, superficial infestation – local cleaning possible.
- Category 2: moderate infestation or hidden areas – professional remediation recommended.
- Category 3: Extensive or deep infestation – remediation by a specialist company with free measurement required.
Ab Kategorie 2 sollte ein Sachverständiger eingeschaltet werden.
Weiter Informationen zur Bewertung von Schimmel finden Sie beim Umweltbundesamt: Download Schimmelleitfaden
The distribution of costs depends on the cause:
- Construction or design defect: Owner or developer
- Incorrect ventilation/heating: Tenants
- Burst pipe/water damage: usually covered by building insurance
An expert opinion helps to clarify the cause objectively and avoid disputes.
If you commission an expert opinion, the costs are always borne by the client initially. The extent to which the costs can be passed on to the other party depends on the individual case.
The basic principle is: Stop moisture = Stop mold. Without moisture, mold cannot grow.
To prevent mold growth permanently, the cause must be identified. The most common causes are:
- thermal bridges
- Incorrect ventilation and heating behavior
- Insufficient heating
- construction defects
- Water damage repaired improperly
There are no standard values for proper ventilation or humidity. The rule of thumb is that at a room temperature of 20°C, the maximum relative humidity should not exceed 60%. This applies to modern buildings constructed since the early 1990s. For older buildings, other lower humidity values may apply.
DIY tests often provide only a general overview of the spores present in the ambient air. They cannot confirm whether a source of mold actually exists.
Professional laboratory analyses (air sampling or material testing) are significantly more precise and, above all, admissible in court, as they detect and document even hidden infestations and the exact spore concentration.
You can find more on this topic here: Mold Test
Moisture & building physics
Thermal bridges are areas in building components where heat is lost to the outside more quickly than in the surrounding structure. This results in locally cooler surfaces where moisture condenses. This moisture can lead to mold growth, structural damage, and increased energy consumption. Typical thermal bridges occur at window reveals, corners, balcony slabs, roller shutter boxes, or poorly insulated component junctions. A professional analysis—e.g., using thermography—clearly identifies these weak points and enables targeted measures. Below is the operating principle of a geometric thermal bridge:
Building moisture refers to the moisture contained in building materials that has entered the material through diffusion, capillary action, or water ingress.
A certain moisture content is normal – it becomes critical when the equilibrium moisture content is exceeded and damage, mold, or salt contamination appears.
There are various methods for measuring moisture content. The most important ones are listed below:
- Drying and CM methods: precise moisture determination of material samples, in some cases also admissible in court.
- Resistance measurement: quick reference values via electrode measurement.
- Capacitive & Microwave Measurement: Non-destructive measurement methods for assessing surface and deep moisture.
- Thermography: Detection of temperature variations and thermal bridges.
In practice, as shown in the figure, the capacitive method is most commonly used.
You can find more information on this topic here: Assessment of moisture damage
The moisture profiles obtained can be compared with typical moisture scenarios (rising damp, moisture from outside, condensation, and hygroscopic moisture). This allows a specialist to pinpoint the exact cause and develop an appropriate remediation plan.
Moisture damage requires expertise, measurement technology, and an understanding of building physics. Only by accurately identifying the cause can a lasting solution be achieved. The analysis of the measurement data obtained is not always straightforward and must be considered in conjunction with other influencing factors.
Preservation of evidence & expert opinions
The cost of an expert report can vary significantly depending on its intended use and scope. In all cases, there is a charge for the on-site visit to collect data. This is typically billed as a flat fee. The cost for preparing a brief report is approximately 450 euros. For a detailed expert report in accordance with the expert guidelines, the costs vary between €750 and €2,000, depending on the scope.
For more information on flat-rate fees for mold damage assessments, click here: Mold Damage
Preservation of evidence is the objective and comprehensible documentation of the condition of a building or damage at a specific point in time.
It serves to avoid subsequent disputes about causes, responsibilities, or the course of damage.
The result is legally admissible evidence of the actual condition.
Preserving evidence is always recommended when:
- Construction work takes place near existing buildings,
- Risse, Setzungen oder Feuchtigkeitsschäden bereits sichtbar sind,
- Renovations or modernizations are planned,
- or legal disputes/insurance issues are to be expected. It can be carried out before the start, during, or after the completion of construction or renovation measures.
An expert opinion must be understandable to the layperson and comprehensible to the expert.
A legally binding expert opinion should include the following mandatory elements:
- Minimum formal information (title, creator, client, project description, site visit, property address)
- Facts / Background (property description, documents provided, spatial scope, any restrictions)
- Measurements (measurement methods, measuring instruments, measurement strategy, measurement results)
- Objective findings without personal assessment (building materials, condition, extent of damage, photos)
- Technical Assessment (Comparison with accepted engineering standards, determination of the cause, technical delineation of responsibilities)
- n (strictly technical)
- Summary / Conclusion
An expert report strictly reflects the technical conditions on site and does not constitute a legal assessment!
DIN EN ISO/IEC 17024 is an internationally recognized quality standard for experts. It certifies verifiable professional competence, formal examination, regular recertification, and standardized quality of expert reports.
Unlike public accreditation, which is valid only nationally, ISO 17024 is recognized worldwide and thus also meets the requirements of insurance companies, government agencies, businesses, and international clients.
For you, this means: An ISO 17024-certified expert operates at a professional and quality level that is at least equivalent to that of a publicly appointed expert—with the added benefit of international quality assurance.
Learn more about ISO 17024 certification here: European Committee for Quality Assurance
Expert opinions are classified, first of all, according to their intended use:
- Private appraisal
- Expert report
- Court-appointed expert opinion
- Arbitration award
Inhalt und Umfang können auch unterschiedlich sein:
- Court expert opinion, complete with all information relevant to the proceedings
- Full expert opinion (private) equivalent to a court-appointed expert opinion
- A brief report, which assumes that the parties involved are familiar with the property. Detailed descriptions of the methods used are omitted. The focus is on the technical assessment.
Practice & Case Studies
An on-site appointment serves to objectively assess the current state of damage.
The affected rooms and building components are systematically inspected, measured, and documented.
The process follows a fixed, transparent pattern:
- Inspection and visual inspection
- Recording of the affected rooms and building components.
- Documentation of abnormalities, damage, signs of odors, or moisture.
- Production of overview and detailed photos.
- Measurements and technical recording
- Moisture measurements (capacitive or resistance) at representative points.
- Surface and room temperature measurements, thermography if necessary.
- Measurement of indoor humidity, outdoor climate data if applicable.
- Comparison with reference values.
- Interim evaluation / on-site meeting
- Brief explanation of initial observations.
- Information on possible causes or further investigations.
- Keine rechtliche Bewertung oder Sofortgutachten – nur technische Einschätzung.
- Überprüfung der Messergebnisse und Fotos.
- Review of measurement results and photos.
- Preparation of a brief report or expert opinion with evaluation and, if necessary, recommendations for action.
- Shipping to the client (digital).
Note:
The on-site appointment forms the basis for every expert opinion.
It represents the condition at the time of inspection and serves as objective evidence for later evaluations or comparisons.
In the case of mold or moisture damage, the damage pattern can change after just a few days—which is why prompt assessment and documentation are crucial.
The cost of an expert opinion is always initially borne by the client, i.e., the person who commissions the expert. However, who ultimately has to pay depends on the cause and the legal situation.
In the case of private expert opinions, the following scenarios can generally be expected:
1. Construction defects (new construction / renovation)
Liability: The developer, contractor, or business owner, if a defect is proven.
→ The expert opinion serves as evidence in the defect proceedings.
2. Rental Apartment – Mold / Dampness
- Cause is structural → Landlord bears the costs.
- Cause: User behavior → The tenant bears the costs. → The expert opinion clearly establishes responsibility.
3. Wasserschäden / Leitungswasserschäden
Covered by: Building insurance or liability insurance, if a claim arises.
→ Some insurers explicitly require an expert opinion.
4. Purchasing Real Estate / Market Value
Paid by: the buyer or seller, depending on who commissions the appraisal.
→ Market value appraisals are investment decisions and are not reimbursable.
Yes, in-person consultations are available.
Generally speaking, written reports and expert opinions are not strictly necessary. Especially if you simply want to know the cause of the damage, an in-person explanation on-site may be sufficient.
If other parties (property management, landlords, tenants, contractors, etc.) are involved, it is always advisable to document the situation in a report.
Home Inspection & Buying Advice
Before the final inspection, you must report any defects to the developer. The developer bears the burden of proof regarding whether the issue constitutes a defect. After the final inspection, the burden of proof shifts. This means you must prove to the developer that the defect existed prior to the inspection and that it is indeed a defect.
An expert can identify defects that laypeople often overlook (e.g., thermal bridges, waterproofing defects, workmanship defects) and can provide an assessment right on site.
A professional inspection will be conducted. During the inspection, we will use non-destructive testing methods to measure the moisture content of the walls, identify any thermal bridges, assess any damage, and evaluate the property’s energy efficiency and overall condition.
Learn more about this topic here: Building inspections and construction supervision
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