Solutions For Mould and Black Spots on Windows, Walls and Ceiling

Have you noticed black mould, marks and spots on ceilings, walls or near to the windows in your home?

If you have, don’t worry; thousands of homes in the UK suffer from this issue but there is a quick, permanent solution and it may cost less than you think.

Last week a friend of mine asked me to check her roof, she’d noticed some damp patches on her ceiling near to the window in her bedroom.

It didn’t take me long to realise that the issue had nothing to do with the roof.

Here’s a couple of photos I took:

Mould on windows

Black marks, spots and mould on the window frame and wall

Mould forming on the ceiling near the window

Although I had a good idea of what was causing this, I asked a few probing questions:

Q) How long have you lived here and had you seen this before?

Q) Have you made any changes to the home since last winter?

Q) Any lifestyle changes that would result in you creating more moisture in the bedroom?

The answers were predictable and confirmed what I already knew:

A) I’ve lived here five years and never had any issues like this before.

A) I had new triple glazing windows installed in April this year.

A) My partner moved in with me recently, so two people are now sleeping in the bedroom.

New Windows and Black Spots/Mould

Did you know that windows installed to a “new build” property should have “trickle” vents (or similar) fitted?

Window vents, trickle vents

Window trickle air vent

These vents aren’t big enough to adversely affect your heating bills, but they do help to remove moisture from the room.

Unfortunately, while the regulations state ventilation is mandatory for newly built homes, there’s no requirement to install them when replacing windows in existing homes.

So did the installer fit these vents when replacing my friend’s windows?


So my friend replaced her old drafty timber-framed windows with airtight sealed triple glazed units with no vents, AND because her partner is now sleeping in the same room as her, they are now creating twice as much moisture via their breathing.

Why Didn’t She Notice The Issue Earlier?

The original windows were 30 years old and drafty so they provided natural ventilation.

Those windows were replaced and her partner moved in during the summer but it wasn’t until November that the outside temperature dropped and the first frosts were seen.

A warm, unvented room + extra moisture + cold windows/walls = condensation.

Condensation, if left unchecked will lead to damp walls, ceilings, black spots and mould.

Here is an extreme example, the photo was taken in another house:

Condensation around window

Excessive condensation around the windows can lead to mould and damage

If you think the mould shown in the first two photos on this page isn’t too bad, don’t forget that the photos were taken in mid-November.

As it gets colder outside, more moisture will form, and the mould will spread further. You might be surprised at how quickly it can spread.

Other Causes of Black Mould/Spots on Walls, Windows and Ceilings

Upgrading the windows isn’t the only cause of mould/condensation.

Loft and cavity wall insulation may improve the thermal efficiency of the home, but to some degree will also prevent moisture from escaping.

You should also consider any lifestyle changes that have occurred which may increase the volume of moisture being created in the home or room.

For my friend, the catalyst was her partner sharing the bedroom with her, but do consider:

  • Additional occupants of the home.
  • Drying clothes on radiators when it’s cold outside.
  • Roof leaks, pipe leaks or faulty extractor fans not removing the moisture.
  • Homes with newborn babies often experience mould/condensation in the winter – windows are kept shut, the heating on high, items sterilised with hot water which produces moisture etc. This all creates a perfect environment for mould.

Now You Know The Cause – What Next?

Now you know the cause of the mould (occupants creating moisture in the winter and lack of ventilation), there are two steps you can take to prevent mould from forming:

1 ) Install trickle or passive air vents.

2 ) Reduce the amount of moisture created.

1 – Install Trickle Vents and/or Passive Vents

If your home doesn’t have trickle vents on the windows, they can be retrofitted to most Upvc frames.

There are tons of videos online explaining how to do this. I would suggest you start by watching this one.

Trickle vents alleviate most condensation related problems of mould and dampness but there are occasions when they aren’t 100% effective:

  • The home is unusually airtight (excessive insulation, triple glazing, waterproof paints etc.).
  • Occupants are creating exceptionally high levels of moisture (clothes on radiators etc.).
  • Occupants were not opening windows or too few windows with trickle vents.

This is when a Passive Input Ventilation system should be installed.

I recommend these to landlords as their tenants won’t be able to wreck the walls and ceilings through condensation damage.

Air vent system to reduce condensation

Passive air vent (PIV) system. The reviews speak volumes

This vent system has many benefits:

  • Requires little ongoing maintenance.
  • Cheaper than re-plastering damaged walls and ceilings.
  • Low wattage so won’t cost a fortune to run.
  • Can be fitted with an optional wall-mounted switch so it can be turned off in the summer.
  • Removes moisture and unpleasant smells so will improve the overall air quality in the home.

I’m a huge fan of passive input ventilation systems, but I’m not the only one.

Here’s a review from an Amazon customer:

Our house had black mould on the walls and damp Windows (we have an old house with solid walls). We bought this and improved ventilation in the rest of the house. We also got a condensing tumble dryer. The average humidity is now 40% (compared with 60-70 before) and I haven’t seen any moisture anywhere all winter. The house also smells so much better. I would highly recommend this!

The Passive Input Ventilation system has a 5-star rating on Amazon and over customer 230 reviews.

Read Reviews of the Drimaster PIV

2 – Reduce the Amount of Moisture Being Created in the First Place

This is easier said than done but the general advice is:

  • Keep kitchen and bathroom doors closed when in use.
  • Use lids on cooking pots and pans.
  • Don’t dry clothes on radiators, use a tumble dryer instead.
  • If you must dry clothes on the radiators, do so in a room where you can leave the window slightly ajar.
  • Make sure all bathrooms and kitchens have powerful extractor fans especially if there are no windows in the rooms.

What to do if You Discover Mould or Black Spots in the Summer

Mould usually forms as the result of condensation which is most common in the winter or any time the temperature drops below the dew point.

If you see mould, black spots or dampness in the summer, it will most likely be the result of:

Installing vents may help to alleviate the symptoms of these issues but certainly won’t solve the underlying cause. You’ll need to investigate the issue further rather than installing vents.

Specific Advice For Landlords

I have two friends that own properties which they rent out, both have experienced issues with damp, mould and condensation.

In both cases, it was partly the fault of the tenants and partly due to the design of the buildings.

Here are my top tips for landlords:

  1. Make sure the windows have trickle vents installed, especially in the bedrooms.
  2. PIV systems are great for homes that have previously suffered from condensation related damage; this is a no-brainer in my opinion.
  3. Install door closure devices on bathroom and kitchen doors, so they’re forced shut, this keeps the moisture from escaping into other parts of the home.
  4. Invest in good quality and powerful extractor fans in the bathroom and in the kitchen cooker hood. This is a must if the rooms don’t have their own windows. Bathroom extractor fans should be hooked up to the light switch with a delayed switch-off timer, so they continue to work after the occupants have left the bathroom. Personally, I would install a bathroom extractor fan even if there’s a window, some tenants keep the windows closed, and this will extract the moisture preventing mould formation.
  5. If there’s enough space in the kitchen, install a tumble dryer, so the tenants don’t need to dry their clothes on the radiators.
  6. Add a clause to the tenancy agreement forbidding them from drying clothes on the radiators and place a clothesline in the garden if possible.

Painting and Decorating Over Mouldy Walls and Ceilings

Once you’ve fixed the underlying cause of the mould, you can clean the mould off and treat the surface with a chemical prior to painting or decorating.

The best chemical to use is Benzalkonium Chloride, it’s a fungicide that will completely kill off any mould spores on the wall or ceiling.

Read my review of this moss and mould treatment product here.

Conclusion and Additional Tips

As you now know, ventilation is part of the solution for winter mould, but if you have wardrobes or other furniture pushed tightly against a cold wall, the area behind the furniture could still get stale and mouldy.

As a general rule of thumb, there should be a two-inch gap between any external walls and furniture.

Mould on walls and ceilings can be prevented, and it doesn’t need to cost a fortune.

You should start by investigating the root cause of the mould; it will most likely be either rising/penetrating damp or condensation related.

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