Black spots along the top of a bedroom wall in a rented flat are nearly always condensation damp, and the government’s own guidance says it is “totally unreasonable” to blame whoever lives there. That doesn’t let you off entirely. The habits that reduce it are free, a small patch is yours to clean, and anything larger, or anything that keeps coming back, is for the landlord to investigate. I started by looking up whose problem damp actually is, before sorting out which habits were worth bothering with, and the answer begins with the building, not the tenant.
Whose problem it is: the three kinds of damp
Landlords in England are expected to follow guidance that sorts damp into three causes. Condensation damp is “moisture generated inside the home” that “cools and condenses onto colder parts”. Penetrating damp is “water that gets into the building from outside due to defects in the walls, roofs, windows or floors”. Rising damp is “moisture from the ground that rises up through parts of the buildings in contact with the ground” (GOV.UK, damp and mould guidance).
Of those three, your routine only touches the first. Even on that one, the guidance is blunt. It states “it is totally unreasonable to blame damp and mould in the home on ‘lifestyle choices’”, and adds that “tenants cannot be expected to reduce moisture levels if their home does not enable them to do so.” Nobody can stop showering, cooking or drying clothes. If a flat can’t cope with those, it has a ventilation or insulation fault, which sits on the landlord’s side of the line.
The smell is the least of it. The real reason to care is health, and the same guidance names the people most at risk, including those with “allergies, asthma, COPD, cystic fibrosis, other lung diseases and cardiovascular disease”. So if someone in a shared house has asthma, the mould in their room is a health problem first. Looks come a long way behind.
Why it shows up on the coldest wall in the coldest month
Condensation needs warm, damp air and a cold surface to meet. According to the guidance, homes “that are insufficiently insulated and heated are more prone to the build-up of moisture and condensation on the inside of external walls and windows”. This is why the wall by the hallway stays clean. The mould turns up on the outside wall: the top corner, behind the wardrobe, round the window frame. Those are the coldest spots in the room.
The timing works the same way. In July, the water from breathing, from washing on a rack and from a bathroom door left open went straight out of an open window. By September the heating is off, the nights are colder and the windows stay shut, so it settles on the coldest wall instead.
The cheap habits that are worth doing anyway
The guidance won’t blame tenants, but the habits are still worth keeping up. They’re free, and any landlord or surveyor will start by asking whether you’ve tried them. Shelter’s list for private renters is short: “open windows regularly, cover pans when you cook, dry clothes outdoors or in a dryer, close internal doors when you cook or shower, use extractor fans in the kitchen and bathroom, leave a gap between furniture and external walls, wipe condensation from window sills each morning” (Shelter).
Forced to choose two, I would go for these. First, closing the bathroom and kitchen door during a shower or while cooking keeps the steam in with the fan instead of letting it wander into the bedroom. Second, moving a wardrobe or bed a few centimetres away from an outside wall lets air get behind it, which is exactly where the worst patches tend to hide. Wiping the sills each morning takes under a minute per window, and it belongs with the other small jobs in a weekly cleaning schedule rather than being left for the weekend.
Which habit does the most good depends on who you share with. In a shared house with one bathroom and five showers before nine, the fan and the shut door carry most of the load, and the rows are usually about whoever keeps leaving it open. A couple has two people’s laundry going into one bedroom, so the rack should live in the room with the fan. Living alone, a rack of washing in the one room you actually use is the largest source of airborne water you control, and drying it indoors without adding to the damp is its own small set of habits worth getting right.
Photo: Ron Lach via Pexels
The bathroom fan: what it is meant to move
Until I looked it up, I didn’t know the building regulations set a minimum rate for extractor fans. Approved Document F, which is the ventilation part of the Building Regulations for England, gives minimum rates for fans that run intermittently. A bathroom needs 15 litres per second. A kitchen with a cooker hood that extracts outside needs 30 litres per second, and a kitchen with no hood, or with one that only recirculates, needs 60 litres per second (Approved Document F, Volume 1, Table 1.1). A separate toilet needs 6 litres per second. Lots of older flats weren’t built to those figures, but they still tell you roughly what a working fan ought to manage.
The same document says “all rooms with external walls should have background ventilators”. Those are the trickle vents running along the top of the window frame. Shut them, paint over them or tape them up to stop a draught, and the room has lost its background ventilation. For a bathroom without a window, the fan should have controls that “continue to operate the fan for at least 15 minutes after the room is vacated”. If the fan stops the second the light goes off, it wasn’t fitted the way the guidance intends.
A rough check works on any fan. While it’s running, hold a sheet of toilet paper against the grille and see if it stays put. If it drops, report the fan instead of living with it, because the steam it is supposed to shift is ending up somewhere else in the flat.
Cleaning what is already there safely
Small patches are your job, and the guidance explains how to do it. It says “most tenants could reasonably be expected to remove condensation and very small amounts of mould using an appropriate mould and mildew cleaner”, whereas “larger areas of mould should only be addressed by qualified professionals” (GOV.UK, damp and mould guidance). There’s no size in square metres, so my reading is a patch you can wipe off in a few minutes. A whole wall is not that.
What you clean it with matters as well. The guidance says “mould and mildew products should be used in preference to bleach, for health and safety reasons”, which surprised me, since bleach is the thing most people grab first. Whatever the size of the patch, “the person removing the mould should wear protective equipment, such as a mask, gloves and goggles”, and “windows should be left open during and after the clean up activity”. Scrubbing puts spores into the air, and breathing them in is the thing to avoid. Throw the cloth away when you’ve finished. Don’t dry-brush the patch either: that sends the spores into the air, when the point is to get them onto the cloth.
When it is the landlord’s job, and how to report it
If the habits are in place and the mould still returns, the building has a fault that wiping won’t fix. Shelter’s advice at that stage is to “tell your landlord if you’ve taken these steps but still have damp and mould”. The landlord “should check why the property cannot cope with everyday living” and “fix the underlying problem, such as not enough insulation or ventilation” (Shelter). Not enough insulation or ventilation is a description of the building, and the building is theirs.
How you report it has a lot to do with whether it gets fixed. Do it in writing, with dated photos and a list of what you’ve already tried, so the “just open a window” reply is answered before it arrives. Shelter says to “keep a record of all conversations, emails and messages” and to let the landlord in for an inspection. If the landlord can’t find the cause, “they should ask a damp surveyor”, and “you do not have to pay for this”. The photos, messages and any surveyor’s report should go with the tenancy agreement, which is precisely what a paper and admin filing system is for. When the problem is serious and nothing is done, you can “ask your council for an environmental health inspection”, and “the council can order your landlord to fix damp and mould”. That comes after the written report. It doesn’t replace it.
Tenants of councils and housing associations have legal deadlines working for them. Awaab’s Law has covered social landlords in England since 27 October 2025. They must investigate significant hazards, including damp and mould, “within 10 working days” of finding out about them, send a written summary “within 3 working days of the conclusion of the investigation”, and, where they find a significant hazard, do the safety work “within 5 working days of the investigation concluding”. Emergencies have to be dealt with “within 24 hours” (GOV.UK, Awaab’s Law timeframes). The guidance says it “refers specifically to Awaab’s Law in the social rented sector”, so I’m not suggesting those deadlines cover private tenancies.
What I would not bother with
Anti-mould paint over a patch on a rented wall is one I’d skip. It covers up the symptom on a wall that isn’t yours, and while the wall stays cold and the room stays unventilated, the mould just grows back next to it. I also wouldn’t use a dehumidifier instead of a working fan and open trickle vents. It pulls the water out once it’s already in the air, it costs money to run, and it’s compensating for somebody else’s poorly ventilated flat. And I’d leave the hygrometer on the shelf, since there’s no humidity target in the guidance for it to help you hit.
Where I would put the time: the free habits, the toilet-paper test on the fan, one careful clean of the mould that’s already there, and a dated message to the landlord if it comes back. Most of the other cleaning articles here are about not doing more work than a job needs. This one is about turning down a job that was never yours in the first place.
