Each case is unique and requires individual consideration. With this in mind, we strongly advise against self-diagnosis or carrying out remediation without consulting an expert. Doing so could recklessly endanger your health. A detailed analysis by experts, such as Building Biology Testing Specialists IBN, is always necessary, as is professional remediation.

Common causes of mold growth

Construction defects and structural damage

• Moisture from the ground caused by groundwater and/or rainwater
• Lack of waterproofing and/or a vapor barrier in basement floors/walls and other building components in contact with the ground
• Structural defects, such as uncontrolled water ingress through the roof
• Leaks in pipes or rain gutters

Causes related to building physics

• Insufficient surface and/or core temperatures of building components. This can lead to high relative humidity and the formation of condensation:
  (a) over large areas due to poor thermal transmittance (U-value) and/or
  (b) in specific, localized spots due to thermal bridges. Example of thermal bridges include exterior corners of the house, window reveals, cantilevered balconies, and radiator niches.
• Using building materials that do not buffer moisture (non-hygroscopic)
• Improperly installed interior insulation, such as excessive thickness, unsuitable materials, or installation defects. Behind interior insulation, building components become colder, causing the dew point – the level at which water vapor condenses – to shift further inward.

Occupants/users

• Incorrect heating and/or ventilation strategies:
  • Insufficient air exchange rates, such as inadequate or infrequent ventilation
  • Frequently turning down the heat, such as reducing the temperature at night, during working hours, or on weekends, and/or continuously leaving windows tilted open results in the excessive cooling of building component surfaces (see „Causes Related to Building Physics“ above)
  • Ventilating or heating colder rooms, such as bedrooms, with air from warmer and/or more humid rooms, such as bathrooms or living rooms
  • Ventilating cool basement or ground-floor rooms in summer with warm (and humid) outside air increases relative humidity
• Above-average moisture levels caused by showering, bathing, cooking, having many plants (which evaporate water when watered), having pets, and having too many occupants…

In cases of construction defects or structural damage, liquid water usually enters the building, which makes the damage easy to identify. In other cases, mold growth is caused by water vapor in the air. Here, an interaction usually occurs between causes related to building physics (see „Causes Related to Building Physics“ above) and user behavior (see „Occupants/Users“ above). For example, mold may develop in areas with inadequate thermal insulation, a problem that can be exacerbated by improper use by occupants. However, this can be prevented through proper heating and ventilation strategies.

1 Excessively moist indoor air and condensation on windows almost guarantee the growth of mold.
2 Mold growth is common in exterior corners of the house (which act as thermal bridges), especially behind baseboards.
3 Professional mold remediation requires protective clothing, a dust mask that filters out microscopic particles (NP95), and an industrial vacuum cleaner with a HEPA filter.
4 Improperly installed interior polystyrene insulation can lead to mold growth.

Possible consequences

• Health issues related to toxic molds, their spores, allergens, and toxins (mycotoxins) may include respiratory diseases, asthma, allergies, skin and mucous membrane damage, lung infections, fungal infections (mycoses), organ damage, impaired immune and central nervous systems, and cancer. A poor indoor climate, including cold walls, can trigger diseases such as rheumatism, gout, colds, and sinusitis (often chronic sinusitis).
• Unpleasant odors negatively affect well-being, a fact that is often underestimated.
• Favorable conditions for insects, bacteria, and mites (including pathogens)
• Building structures may deteriorate due to the activation of salts, frost, mold, corrosion, and insects. This can result in damage to furniture, books, files, clothing, etc.
• Higher heating requirements due to increased masonry moisture that degrades thermal insulation

Remediation and prevention options and strategies

Taking prompt remedial action is generally advisable to prevent the spread of mold.

Repair of construction defects, structural damage, and weaknesses related to building physics:

• Waterproofing against rising water using barrier membranes, slurries, drainage systems, and layers of water-permeable round gravel, moisture-buffering restoration renders/plasters, correcting structural defects
• Repairing pipe leaks
• Improving U-values for exterior building components and windows and preventing thermal bridges
  Caution: Do not seal or install new windows without consulting qualified building professionals. This can shift the dew point to other weak areas, such as window reveals or building corners, which can lead to mold growth. It generally only makes sense to replace windows when the exterior walls and possibly the roof are insulated simultaneously.
• Remove interior insulation (including so-called insulating wallpaper) unless it is hygroscopic and vapor permeable. Remove sealing paints and wallpaper.

Mold removal

• Properly remove mold-infested materials such as wallpaper, drywall, plaster (where applicable), and porous masonry. Also, completely remove any easily removable building components, such as flooring, wood paneling, and interior insulation. Scrape or plane the surface of non-removable materials. Wear personal protective equipment, such as an N95 (FFP2) mask. For large infestations, for example, use plastic sheeting to contain the contaminated area and prevent the spread of mold fragments and spores. For small infestations, it may be sufficient to use a HEPA vacuum cleaner continuously during remediation.
• If remediation cannot be performed promptly, seal mold-infested areas with plastic sheeting. Do not use rooms with extensive damage.
• After mold removal, it is often necessary to quickly and professionally dry damp building components. Prefer vacuum-based methods. Do not use gas-powered building dryers because they release significant amounts of water vapor. Do not use fan heaters, as this can cause mold spores to spread uncontrollably.
• Use HEPA air scrubbers in conjunction with mold removal and drying.
• Thoroughly clean the affected room or building to remove deposits of mold spores, allergens, toxins, and other irritants (so-called secondary contamination). Use a suitable vacuum cleaner equipped with a HEPA filter or an H class industrial vacuum cleaner. Wash with cleaning agents that effectively dissolve grease. Frequently change the cleaning water and cloths. Vacuum cleaners without appropriate high-efficiency filters can stir up and spread mold spores throughout the house!
• Disinfection measures are generally unnecessary and counterproductive because the goal is not to kill mold. Even dead mold can cause allergic reactions and irritation. The key is to remove all mold fragments, spores, allergens, toxins, and irritants. If temporary disinfection is necessary, such as until professional remediation can be performed or in areas where remediation is not feasible due to moisture issues, use a solution containing 70% to 80% alcohol. Note that alcohol poses a fire and explosion risk in large quantities or in poorly ventilated areas. As an alternative, use a solution containing 10% to 30% hydrogen peroxide. Wear safety goggles and gloves! However, avoid using fungicidal agents due to the associated health risks. Vinegar or vinegar essence is suitable only for wiping down smooth, non-hygroscopic surfaces. Vinegar becomes ineffective on mineral building materials due to chemical reactions.

Mold prevention

• Use a hygrometer to regularly check the humidity level. The lower the indoor humidity, the less likely condensation and mold growth are to occur. Increase ventilation when the relative humidity reaches 60% or higher. Also, ventilate more frequently in winter if there are cool building components and the humidity levels are between 40% and 50%. If ventilation is insufficient, which is often the case in below-ground rooms during summer, use a dehumidifier. Due to their high power consumption, dehumidifiers should only be used temporarily.
• The warmer the air, the more moisture it can hold.
  • 10°C (50°F): 9.4 g/m³
  • 20°C (68°F): 17.3 g/m³
  • 25°C (77°F): 23.1 g/m³
• When cold outdoor air is heated, it absorbs moisture from building materials, furnishings, and other sources. Based on this, the following ventilation strategies are recommended: In cool weather, cross-ventilate by opening windows and doors wide for a few minutes several times a day. The colder and drier the outside air, the shorter the ventilation periods can be. On humid, hot summer days, it is best to ventilate primarily late at night or early in the morning rather than during the day. This is especially true for basements and lower-level rooms.
• Ventilation is especially important after showering, bathing, cooking, and cleaning.
• Ensure sufficient air exchange, especially at night in the bedroom. For example, open doors to sufficiently heated adjacent rooms or tilt windows (see „Occupants/Users“ above). People release a lot of moisture through breathing and sweat (ca. 0.5 liter / 16 ounces per person!).
• Install supply air inlets in windows, use a decentralized or centralized ventilation system including an exhaust fan or exhaust air vent in the bathroom and kitchen.
• In winter, heat the space sufficiently, ideally with a radiant heating system such as wall or baseboard heaters or a „true“ tile stove or grundofen masonry heater.
• Ensure rear ventilation of interior furnishings and cabinets against exterior building walls with a clearance of at least 10 cm (4 in). Remove wall hangings if necessary.