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Mould in Berlin’s old buildings: Why the most beautiful apartments in the city have a wet secret

21 July 2026 · 6 min read

Where does mold come from in Berlin’s old buildings, and when does it become dangerous? In short: Most often, there is a combination of moisture, cold exterior walls and too little ventilation behind it. It becomes dangerous especially in large, recurring infestations in rooms where you spend a lot of time. Small, fresh spots can often be removed yourself; in case of stubborn infestation, the cause must be clarified by a specialist.

There is this moment in Berlin’s apartment life that is almost romantic: you move into an old building apartment with plaster on the ceiling, bay windows and parquet floors, which tell a little story with every step. Four meters of ceiling height, light that falls through old sash windows. And then, somewhere in November, when the first real rain comes and the heating runs at half power, you discover it: a dark shadow behind the wardrobe, a stain in the corner of the room, a diffuse pattern on the cold exterior wall.

Between the back houses of Kreuzberg, Prenzlauer Berg Gründerzeit buildings and the concrete block buildings in Marzahn, countless apartments share the same problem. Moisture and mold are not a niche topic for building experts, but something that affects shared kitchens, family bathrooms and bedrooms. Because the topic begins so invisibly and ends so uncomfortably, it is worth a look.

An underrated mass phenomenon

There is no comprehensive official statistics, but various surveys point in a clear direction: Moisture and mold damage are a widespread problem in the German housing stock. In a tenant city like Berlin, where a large part of the housing stock consists of old buildings and buildings in need of renovation, the topic is particularly present. Moisture damage is one of the most common housing defects of all.

Anyone who suspects persistent infestation should think of specialists early on – for example, providers who specialize in Professional mold remediation in Berlin And are specialized in the Brandenburg region and can assess the difference between superficial flooring and a deeper moisture problem. This very distinction determines whether a stain remains a cosmetic annoyance or becomes a tangible construction and health problem.

Why are Berlin apartments so prone to this?

Mould needs one thing above all: moisture. And it finds many ways into the walls in the city. In old buildings, it is often poorly insulated exterior walls, so-called thermal bridges on window sills and corners of rooms as well as rising moisture from the masonry. Cold wall surfaces act like a collector: when warm, humid room air hits them, the water condenses – similar to a frosted bottle in summer.

In addition, there is the modern daily life in the living room. Taking showers, cooking, drying laundry on the stand in the living room, plants, aquariums – a multi-person household quickly brings several liters of water per day as moisture into the room air. In well-sealed but poorly ventilated apartments, this moisture remains where it doesn’t belong. Ironically, many energy renovations have exacerbated the problem: new, dense windows in an otherwise old building prevent the previous “unvoluntary” air exchange through leaky cracks. If the ventilation behavior is not adapted, the moisture accumulates.

However, it is not always the fault of the residents’ behavior. Leaky roofs, damaged pipes, cracks in the facade or a lack of building waterproofing in the basement can permanently let water into the building. This is exactly where one of the most common points of contention between tenants and landlords lies: Is the mold a result of a lack of trees or poor ventilation? The answer is rarely clear – and that is why it is important to have it clarified professionally, instead of hastily asking the question of blame.

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When the stain becomes a health issue

Mould is not just an optical problem. Mould spores and sometimes volatile substances are released into the room air, which can affect health, especially with prolonged exposure. Mould in the interior is considered a risk to health – especially for people with respiratory diseases, allergies or weakened immune system as well as for children.

Typical complaints range from irritated respiratory tract, frequent coughing and red eyes to an exacerbation of asthma and allergic reactions. It is important to be honest rather than panic: a small stain on the window frame does not make anyone sick overnight. But a large-scale, recurring infestation in the bedroom, where you spend a third of the day, is a serious signal – especially in a city where housing space is scarce and many affected people simply cannot afford to move.

What you can do yourself – and where the line is

Part of the Berlin mold problems can be significantly reduced with your own behavior. Several times a day, opening windows wide and letting in fresh air for a few minutes has proven to be more effective than permanently lowering windows, which in winter mainly cool down the basements. Furniture should be a few centimeters away from the outer wall so that air can circulate. When cooking and showering, it helps to close doors and then ventilate them specifically. A simple hygrometer that shows the humidity level costs little and creates surprisingly much clarity.

Small, fresh surface stains on smooth materials can often be removed yourself, provided you follow the usual protective instructions. But there is a clear limit. If the infestation spreads beyond a plate-sized area, it will always reappear after wiping, if it is in wallpaper, plaster, joints or behind coverings, or if it smells musty without anything visible to be found, then DIY is the wrong strategy. Painting over the stain only fights the symptom, not the cause – and the mold continues to grow in hiding.

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Why professional renovation is more than just “cleaning up”

A serious mold remediation does not start with the brush, but with the question of why. Specialized companies first measure the humidity in walls and room air, find the source and clarify whether it is a construction problem, a use problem or a combination. Only then is the infestation removed professionally, the affected material removed if necessary and the area treated so that the fungus does not return. The decisive factor is the permanent solution of the underlying cause: Only when the moisture source disappears does the mold disappear permanently.

A regionally anchored provider that covers exactly this chain combines mold remediation with adjacent fields such as building waterproofing, wood protection and sponge remediation – an advantage if moisture is not only superficial, but in the masonry or the installed wood. This allows a problem to be addressed holistically rather than in individual measures, and residents get a point of contact who has both the cause and the secondary damage in mind.

Tenants, owners and the matter of responsibility

For tenants, the following applies: Moisture and mold should be reported to the landlord promptly and in writing, ideally with photos and date. Those who document the defect are in a much better position to clarify the situation. Tenant counseling centers help to place their own position in the often delicate relationship between causation, burden of proof and rent reduction. Owners, on the other hand, are well advised not to ignore infestations: Untreated moisture will attack the building structure in the long term and turn a manageable renovation case into a costly building damage.

In the end, mold in Berlin is above all one thing: a topic that should be taken seriously, but not dramatically. If you look early, ventilate properly, clarify the causes and bring in experts in time in case of stubborn infestation, you protect your health, your wallet and a piece of Berlin’s living culture. The characteristic old apartments in this city deserve to be taken care of – including dry walls.