The wall is not dirty, and it is probably not your lifestyle. Water is arriving from somewhere, and the pattern on the wall says where.

What the wall shows

Nothing is saved and nothing leaves the page. Mark only what you can actually see or smell — not what you suspect. Then mark the facts about the home; several of them quietly change whose problem this is.

Why the kind of damp decides everything

• Condensation, rising damp, penetrating damp and a leak are four different problems wearing the same stain. One is water made inside the home meeting cold surfaces; one is ground water climbing a wall that has lost its barrier; one is rain getting through the outside of the building; one is a pipe or a roof failing. They are treated in opposite ways, and treating the wrong one wastes months while the wall gets worse.
• The pattern carries more information than the stain. Where it sits — corners and cold outside walls, or a level band above the skirting, or directly below a bathroom — when it grows — after rain, in cold weather, after showers — and what edge it has, are what actually separate the causes. A photograph a week, dated, is worth more than any adjective.
• You cannot ventilate away a building defect, and you cannot repoint away a lifestyle. Opening windows does nothing for a failed gutter; fixing the gutter does nothing for a bathroom with no working fan. This cuts both ways, and it is why the routing has to come before the argument about whose fault it is.
• "Just clean it and air the place" is the sentence this page exists to answer. Cleaning removes spores from the surface and is worth doing — carefully, not by dry-brushing. It does not touch the cause. Mould that returns to the same place within weeks of cleaning is a moisture problem announcing itself, and its return is itself evidence worth photographing.
• Some of the causes are structural, and structural causes are normally the building's to fix, not the occupier's. A damp-proof barrier, the roof, the gutters, the pointing, the pipes inside the walls, an extractor fan that was never fitted: an occupier cannot repair any of these, whatever they do with the windows. What exactly a landlord must do differs by country — but who is physically able to fix it does not.
• Mould is a health matter, not only a repair. The link between damp housing and respiratory illness is one of the most consistent findings in housing research, and it is strongest for children, for asthma, and for anyone whose immune system is compromised. That belongs in the first sentence of every report, because it changes the urgency everywhere.

The four ways water arrives

This is the sort the tool applies. Each row says what that cause commonly looks like — and every answer the tool gives you comes with the observation that checks it against your own wall.

• Condensation. Water made inside — cooking, showers, drying clothes, breathing — landing on the coldest surfaces: windows in the morning, corners of outside walls, behind wardrobes, bathroom ceilings. Spotty black mould rather than a stain, worst in the cold months. The only one of the four where habits play any part — and even there, missing extractor fans, single glazing and walls too cold to keep dry are the building's side of it.
• Rising damp. Ground water climbing the base of a wall that has lost its barrier: a level tide mark with a defined top edge, usually below a metre, on a ground floor or basement, sometimes with white fluffy salts. Rare — much rarer than it gets blamed — and structural when real. No amount of ventilation touches it.
• Penetrating damp. Rain coming through the shell of the building: a patch that darkens during or after wet weather, anywhere on an outside wall, often opposite a failed gutter, cracked render, missing pointing, or earth piled against the wall outside. It follows the weather, not the season.
• A leak. The building's own water: a ceiling ring or a sagging patch below a roof, a bathroom or a neighbour; dampness under a sink, around a bath, behind a toilet, near a radiator. It follows use or rain, it does not care about cold, and it is the one that grows fastest — an active leak is a today problem, not a this-month problem.
• The two questions that separate them. Does it follow the rain, or follow the cold? And is the water coming out of the wall, or landing on it? The first is a diary; the second is a piece of kitchen foil taped tight over the patch for two days — wet on the room side means condensation, wet underneath means the wall itself is wet.

“It is your lifestyle” — and what is actually yours

Almost everyone with a mould problem in a rented home is told, sooner or later, that they caused it. Sometimes part of that is even true. Here is how to keep the conversation factual.

• Living produces moisture, and living is not negligence. Cooking, washing, breathing and drying clothes are what homes are for. A home that cannot cope with being lived in — no working fan in the bathroom, no vent in the kitchen, walls so cold that ordinary air condenses on them — has a building problem, whatever anyone says about pan lids.
• Drying clothes indoors is the accusation you will hear most. If there is a dryer, a balcony or a drying room, use them and say so. If there is nowhere else — which is the usual case — dry them in one room with the door shut and a window cracked or a fan running, and put in writing that no alternative exists. That single sentence moves the conversation from your habits to the building's provision.
• What you can genuinely change: lids on pans, the bathroom door shut and the fan or window on during and after showers, furniture a hand's width off cold outside walls, brief cross-ventilation after cooking and washing, heating kept steady rather than off all day in the affected room. Do them, and date when you started — not because you are on trial, but because doing them and photographing the mould's return is what proves the cause is not you.
• What you cannot change, whatever you do: a missing or broken extractor fan, single glazing, an uninsulated cold wall, a failed gutter, cracked pointing, a bridged or absent damp barrier, a leaking pipe in the wall. Anyone who tells you to ventilate your way out of that list is asking you to fix the building with a window handle.
• The foil test settles the loudest argument. Tape kitchen foil tightly over the patch, sealed at the edges, and leave it for a day or two. Droplets on the room side: the moisture is in the air — condensation. Damp underneath: the wall is wet from inside itself — rising, penetrating or a leak, and no habit of yours produced it. Photograph both sides with a date.
• Never accept a diagnosis delivered in one glance. “That is just condensation” from the doorway, with no moisture meter, no look outside at the gutters and no question about when it is worst, is a guess with a rent attached. You are entitled to describe the pattern precisely and ask that the answer engage with it.

What to do, in order

The first three cost nothing and are worth doing whatever the cause turns out to be.

• Start the record today. One photograph of each affected place, with the date, from the same spot each time, weekly. Add a line for the weather. Two weeks of this is usually enough to see whether it follows rain, cold or showers — and it is evidence nobody can talk over.
• Run the foil test on the worst patch. It costs nothing, takes two days, and splits the problem in half: moisture from the air, or moisture from the wall.
• Report it in writing, dated, and keep a copy. A conversation on the stairs does not exist afterwards. Describe what you see, where, since when, and when it is worst; name anyone in the home in a risk group in the first sentence; ask for inspection and repair; keep it factual and keep the tone boring.
• Clean visible mould safely, once the photos exist. A proper mould cleaner or diluted white vinegar on hard surfaces, wiped, not dry-brushed; throw away heavily affected soft items; do not sand or scrape large areas. If a large area is involved, or anyone in the house is in a risk group, ask for professional removal rather than doing it yourself.
• Do the occupier-side list and date it. Fans on, lids on, furniture off the cold wall, steady background heat in the affected room if you can afford it — and if you cannot afford it, write that down too, because unaffordable heating is part of the picture, not a confession.
• If the answer is a wipe-down and a lecture, escalate with the record. Repeat the report, attach the photo series and the foil result, and ask specifically what inspection was done of the gutters, the roof, the fan, the glazing or the pipes. Whatever formal complaint route exists where you live — a housing authority, an ombudsman, a tenant organisation — it will want exactly the file you have been keeping.
• Keep paying the rent while you argue, unless someone qualified where you live tells you otherwise. In many places withholding rent has consequences that outlast the damp. Take advice before any step of that kind; the record you are keeping loses none of its force in the meantime.

What people believe, and what is so

The drill: 16 walls

Sixteen ordinary moments — the landlord in the doorway saying “condensation”, the bleach that keeps working for two weeks at a time, the wardrobe against the cold wall, the ring on the ceiling on a dry day, the letter you nearly did not send. Each has an answer that keeps the peace this week, and one that gets the wall fixed. Pick the one that holds up; every answer explains why.

The record card

One card per affected room. The top half is the pattern; the bottom half is the paper trail.

🖨️ Print the card