Condensation on your windows every morning? Why it happens and how to stop black mould

If your windows are dripping every morning and black mould is creeping out of a corner, the water is usually coming from inside the home. Everyday living puts litres of it into the air, and it turns back into water on whatever is coldest. That’s physics, not bad housekeeping, and official guidance in England is clear that damp and mould shouldn’t be blamed on how people live.

This guide follows the HanaHow episode: where the water comes from, why it lands where it does, what it means for your health, what the law says if you rent, and what to do about it. The calculator shows how cold a surface has to be in your room before it gets wet.

Where the water comes from

Breathing, showers, cooking and boiling the kettle all put water into the air. Sandwell Council’s condensation booklet, quoting the Building Research Establishment, says the average UK household puts about 12 litres of moisture into the air every day, and over 20 litres where clothes are dried indoors or paraffin or bottled gas heaters are used. The Energy Saving Trust says a household typically produces up to 100 litres of moisture a week.

A load of washing dried indoors adds about 2 to 2.5 litres on its own, according to a design guide on home laundry from the Mackintosh Environmental Architecture Research Unit at the Glasgow School of Art.

If you don’t have a leak or rising damp, the Energy Saving Trust says the problem is almost certainly condensation.

Why the window gets wet: the dew point

Warm air can hold more water than cold air. When air touches something cold enough, it can’t hold all its water any more, and some comes out as droplets. The temperature where that happens is the dew point.

In a room at 20°C with 60% humidity, the dew point is 12.0°C, so any surface colder than 12°C gets wet. On a cold morning, that’s usually the window. Roger Bisby of Skill Builder calls windows, especially single-glazed ones, passive dehumidifiers: the coldest surface in the room takes water out of the air first.

Put in your own room’s temperature and humidity below to see its dew point. A cheap digital hygrometer shows the humidity.

Cold corners and the wall behind the wardrobe

New windows alone won’t cure it, as Roger Bisby says. If the glass is warmer, the water finds the next coldest thing. UKHSA’s guidance lists the usual places: window frames, corners, and low points on walls behind sofas or wardrobes.

• Corners of outside walls lose heat on two sides, so they’re colder than the rest of the wall. Damp specialist Peter Ward measured one corner at about 9°C, colder than the rest of the wall.
• Behind furniture, air can’t move freely, so the wall stays cold and damp.
• After insulating, condensation can move to whatever is left uninsulated. The Energy Saving Trust gives single glazing in an insulated wall, or a gap in the insulation (often at the top of the wall), as examples.

Mould doesn’t need water running down the wall. A widely used building-science rule of thumb puts mould risk where a surface stays at about 80% humidity. In the 20°C, 60% room, that’s any surface below about 15.4°C, well before it looks wet. The Property Care Association makes the same point: mould can grow without the dew point being reached.

Why it’s worst in the morning

Overnight the heating goes off and the room cools, but the water stays in the air, and you breathe out all night. The same 20°C, 60% air cooled to 16°C reaches about 77% humidity, and at 15°C about 82%. Meanwhile the windows and outside walls get colder, so more of them drop below the dew point. Roger Bisby calls the time the heating goes off “prime time” for condensation. The Property Care Association says the UK’s condensation season usually runs from October to April.

Is black mould dangerous?

UKHSA’s guidance, published with the Department of Health and Social Care and the Ministry of Housing, says damp and mould mainly affect the airways and lungs, and can also affect the eyes and skin. The effects it lists include:

• coughing, wheezing and shortness of breath
• airway infections, including aspergillosis
• asthma, rhinitis and other airway conditions starting or getting worse
• eye irritation, eczema and skin rashes
• poor mental health, from the conditions themselves and from being blamed for them

Everyone is vulnerable, it says, but some people are at greater risk: babies and children, pregnant women, older people, people with health conditions such as allergies, asthma or COPD, anyone with a weakened immune system, people with a mental health condition, and people who are housebound or bedbound. It estimates that in 2019, damp and mould in homes in England were linked to about 5,000 cases of asthma and 8,500 lower respiratory infections.

You’ll read a lot about “toxic black mould”. The US Centers for Disease Control and Prevention says it isn’t necessary to find out what type of mould you have, and that all moulds should be treated the same, both for health risks and for removal. Its occupational health institute adds that some moulds can produce toxins, but the moulds themselves are not toxic or poisonous, and the CDC says no test proves a link between the black mould Stachybotrys chartarum and particular symptoms. Whatever colour it is, get rid of it and fix the damp.

If you or your children have symptoms, talk to your GP. Landlords shouldn’t wait for medical evidence before acting: UKHSA says it isn’t a requirement.

It’s common. The English Housing Survey found damp in 1.4 million homes in England in 2024, about 1 in 20, and in 1 in 10 privately rented homes. Severe condensation was the most common kind.

Awaab Ishak and Awaab’s Law

Awaab Ishak, from Rochdale, died in December 2020, aged 2. The coroner found he died of a severe respiratory condition caused by prolonged exposure to mould in his home, and that “action to treat and prevent the mould, was not taken.” His family’s landlord was told about the mould in 2017, and the advice to his father was to “paint over it”. The flat’s bathroom fan didn’t work effectively and the kitchen had no mechanical ventilation. The coroner found no evidence that the family’s lifestyle was “excessive”: cooking, washing, bathing and drying clothes are normal.

UKHSA’s guidance now says it is “totally unreasonable to blame damp and mould in the home on ‘lifestyle choices’”.

England: social housing

Awaab’s Law has applied to social landlords in England, councils and housing associations, since 27 October 2025. Under the government’s guidance, the landlord must:

• investigate an emergency hazard and make it safe within 24 hours
• investigate significant damp and mould within 10 working days of becoming aware of it
• give you a written summary of what it found within 3 working days of finishing the investigation
• do the work to make it safe within 5 working days of the investigation, if it finds a significant hazard
• start work to stop it coming back within 5 working days if it can, and physically start it within 12 weeks
• find you somewhere suitable to stay, at its own cost, if it can’t make your home safe in time

The 24-hour emergency rule already applies to any kind of emergency hazard, such as a gas leak or a broken boiler, not just damp and mould. From 30 November 2026, subject to Parliament’s approval, the 10-day rules are due to extend to other significant hazards such as excess cold, falls and fire. The damp and mould timescales stay the same.

England: private renting

Awaab’s Law doesn’t cover private renters in England yet. The government’s plan for the Renters’ Rights Act says it will extend it to private renting, with the timing “subject to consultation”. Private renters still have the council’s environmental health team, which can inspect and order repairs, and the Homes (Fitness for Human Habitation) Act 2018, which lets tenants take a landlord to court over a home that isn’t fit to live in.

Scotland

Scotland’s version started on 6 October 2026, and it covers social tenants and most private tenancies, including the common Private Residential Tenancy. Landlords must investigate damp or mould within 10 working days, give you a written summary within 3 working days of the investigation, and, if they find substantial damp or mould, start the repairs within 5 working days. Cases reported before 6 October 2026 aren’t covered by these timescales.

Wales

The England law doesn’t apply in Wales. Since 1 April 2026, the Welsh Housing Quality Standard has set timescales for social landlords: a hazard such as damp and mould that may present a significant risk, caused by defects or disrepair the landlord is responsible for, must be investigated within 10 working days and put right within a further 5 working days, or within 24 hours and then 24 hours more if harm is imminent. If it can’t be put right in time, the landlord must give the tenant a written plan within 5 working days. Private and social landlords in Wales also have to keep homes fit to live in under the Renting Homes (Fitness for Human Habitation) (Wales) Regulations 2022, where damp and mould growth is the first item on the list.

Northern Ireland

We couldn’t find a law in Northern Ireland like Awaab’s Law, with fixed timescales for damp and mould, as of 9 October 2026. Housing Rights, the Northern Ireland housing charity, says private tenants should raise repairs with the landlord first, and the council’s environmental health department can inspect the home and give the landlord legal notices to do repairs. Housing Executive and housing association tenants report repairs to their landlord, use its complaints process if that doesn’t fix it, and may then be able to go to the Northern Ireland Public Services Ombudsman. For advice on your own situation, contact Housing Rights or your council.

What you’ll need

How to stop condensation

There are two jobs: get less water into the air, and have fewer cold spots for it to land on. These come from the Energy Saving Trust, UKHSA and Shelter.

1. Put lids on pans when you cook.
2. Run the extractor fan while you shower or cook, and for at least 15 minutes after, with the door shut so the steam doesn’t spread through the home. No fan? Open the window, and leave it open for at least 15 minutes afterwards.
3. Dry washing outside when you can. If you can’t, a dehumidifier in the room where it dries helps. Shelter says a landlord shouldn’t ban you from drying clothes indoors if you have no outside space.
4. Keep trickle vents open and clear, and open windows wide for at least five minutes a few times a day.
5. Keep the heating low and steady, if you can afford to. Rooms left cold are prone to damp, but the Energy Saving Trust says leaving the heating on all the time just to avoid damp isn’t a sensible answer.
6. Pull furniture a few centimetres away from outside walls so air can get behind it.
7. Leave a gap under internal doors, at least 10 mm, so air can move round the home.
8. Wipe the windows and sills every morning, and squeegee the shower walls afterwards. A window vac speeds it up, and its tank shows how much water was on the glass.

The Energy Saving Trust also says not to fit new draught-proofing in a room that already has condensation. The US Environmental Protection Agency suggests keeping indoor humidity below 60%, ideally between 30% and 50%. We couldn’t find an official UK figure.

Cleaning a small patch of mould

UKHSA says most people can deal with condensation and very small amounts of mould themselves. Fixing the cause matters more than the cleaning: the mould comes back if the wall stays damp.

1. Take a photo first, and draw round the patch if you can. It’s a record if you rent.
2. Wear gloves, a mask and goggles. Shut the door to the rest of the home and open the window, and leave it open afterwards.
3. Use a mould and mildew product rather than household bleach. UKHSA recommends them in preference to bleach, for health and safety reasons. Follow the instructions on the bottle.
4. Wipe it off with a damp cloth, and bag the cloth and throw it away. Don’t brush or vacuum mould off dry, because that throws spores into the air.
5. Never mix bleach or a mould spray with vinegar or other cleaners. Some mould sprays contain bleach, so check the label. UKHSA says bleach mixed with acids such as vinegar gives off chlorine gas, and mixed with ammonia it gives off chloramines, both of which irritate the airways.
6. Paint only once it’s dry and the cause is fixed. Anti-mould paint goes on after the wall is completely dry and the source of the damp has been dealt with. Never paint or wallpaper over mould that hasn’t been treated.

Carpets, soft furnishings and ceiling tiles that go mouldy may have to be thrown away, as UKHSA says it can be hard or impossible to get all the mould out.

When to get a professional

If the mould covers a large area, keeps coming back, or looks like it’s from a leak, get a professional and find the cause. UKHSA says larger areas of mould should only be dealt with by qualified professionals. It doesn’t give a size. The US Environmental Protection Agency says you can usually handle a patch smaller than about 10 square feet yourself, which is just under a square metre.

If you rent

Tell your landlord in writing, with photos, and keep a copy. Shelter has a letter template, and says to keep a record of every conversation, email and message. Shelter’s advice for private renters in England is that your landlord must try to find out what’s causing the damp, and if they can’t, they should ask a damp surveyor, at no cost to you. It also says a landlord shouldn’t tell you to paint over mould that keeps coming back, say it’s just condensation without checking, or tell you to stop everyday things like cooking or showering.

If nothing happens:

• Private renters in England can ask the council’s environmental health team to inspect if the problem is serious. The council can order the landlord to fix it.
• Social tenants in England should use the landlord’s complaints process, then go to the Housing Ombudsman if it isn’t put right. The ombudsman can also help if the landlord doesn’t respond to your complaint.
• Private tenants in Scotland can apply to the First-tier Tribunal (Housing and Property Chamber), which can order repairs.
• In Northern Ireland, Housing Rights can advise on your options, including the council’s environmental health department.

Don’t stop paying your rent. Shelter says you can be evicted for not paying, even if your landlord isn’t doing repairs. You can ask for a lower rent until it’s put right, but your landlord doesn’t have to agree. Housing Rights gives the same warning in Northern Ireland.

Sources

• UK Health Security Agency, DHSC and MHCLG: Understanding and addressing the health risks of damp and mould in the home, updated 1 April 2026. UKHSA: Sodium hypochlorite: general information.
• Sandwell Council: condensation booklet, quoting BRE Good Repair Guide 7, Treating Condensation in Houses. Energy Saving Trust: How to get rid of damp (archived copy). MEARU, Glasgow School of Art: Healthy Low Energy Home Laundering design guide.
• Dew point: the Magnus formula with Alduchov and Eskridge’s coefficients, Improved Magnus form approximation of saturation vapor pressure, 1996. The 80% surface humidity figure is a widely used building-science criterion for mould growth, used in methods such as BS EN ISO 13788; the standards are paywalled, so we treat it as a rule of thumb.
• Skill Builder, Roger Bisby: Condensation gets worse when you do this. Peter Ward, Heritage House: a damp house with paint peeling off walls, measuring a cold corner. Property Care Association: What is condensation and mould.
• US Centers for Disease Control and Prevention: Facts about Stachybotrys chartarum and NIOSH Mold, testing and remediation. US Environmental Protection Agency: A brief guide to mold, moisture and your home.
• MHCLG: English Housing Survey 2024 to 2025, housing quality and energy efficiency.
• Senior Coroner Joanne Kearsley: Awaab Ishak, prevention of future deaths report, 16 November 2022.
• England: The Hazards in Social Housing (Prescribed Requirements) (England) Regulations 2025, MHCLG’s Awaab’s Law guidance for social landlords, the regulations as they apply from 30 November 2026, the phase 2 guidance and the Renters’ Rights Act 2025 roadmap.
• Scotland: Awaab’s Law: guidance for tenants in Scotland and mygov.scot on problems getting repairs done.
• Wales: Welsh Housing Quality Standard addendum on responding to hazards and fitness for human habitation guidance.
• Northern Ireland: Housing Rights on help from the council and repairs for social tenants.
• Shelter: damp and mould in private rented homes and withholding rent for repairs. Oxford City Council: get rid of mould. Housing Ombudsman.