You pull back the curtains one morning and discover something you weren't expecting.
Small black spots have appeared around the window.
The wallpaper feels damp.
Perhaps there's even a musty smell.
Across Preston, this is one of the most common mould problems we investigate.
Homeowners often ask:
👉 "Why is there mould behind my curtains?"
👉 "The rest of the room looks fine, so why is it only here?"
👉 "Is my window leaking?"
In most cases, the answer isn't a leaking window at all.
Curtains can create the perfect environment for condensation by trapping cold air against the wall and restricting airflow, allowing black mould to develop over time.
🪟 Windows Are Naturally The Coldest Surface In The Room
Glass loses heat much faster than insulated walls.
During colder weather, window panes and the surrounding reveals become some of the coolest surfaces inside your home.
Warm indoor air naturally moves towards these colder surfaces.
When the air cools to its dew point, moisture turns from water vapour into liquid water.
This is condensation.
🌬️ Curtains Restrict Airflow
Curtains are excellent at reducing draughts and improving comfort.
However, when fully closed, they also create a pocket of trapped air between the fabric and the window.
This area receives very little air movement.
As a result:
- Moisture remains trapped.
- Surfaces stay colder.
- Condensation takes longer to evaporate.
These conditions are ideal for mould growth.
💧 Condensation Often Forms Where You Can't See It
Many homeowners wipe condensation from the glass every morning.
What they don't see is the moisture collecting:
- Behind the curtains
- On the window reveal
- Along the window sill
- On the surrounding plaster
Because this area is hidden, condensation can remain for hours before anyone notices.
Repeated day after day, black mould begins to establish itself.
🍄 Black Mould Needs Three Things
Black mould grows when three conditions come together:
✔ Moisture
✔ Organic material (such as paint, wallpaper or dust)
✔ Time
Behind curtains, all three are often present.
Once mould spores settle on a persistently damp surface, they begin to multiply.
🏠 Bedrooms Are Often The Worst Affected
Behind-curtain mould is especially common in bedrooms.
Why?
Because overnight:
- Doors are closed.
- Windows remain shut.
- Heating is often reduced.
- Occupants release significant amounts of moisture simply by breathing.
By morning, humidity levels are at their highest.
The colder window area becomes the first place condensation forms.
🌡️ Thermal Bridging Around Window Reveals
It's not always the glass that's affected.
The wall surrounding the window may also be colder due to thermal bridging.
Common causes include:
- Concrete lintels
- Older solid-wall construction
- Limited insulation around the opening
- Structural changes within the wall
These colder surfaces encourage condensation and provide another area where mould can develop.
🌬️ Poor Ventilation Makes The Problem Worse
Everyday living produces moisture through:
- Showering
- Cooking
- Washing
- Drying clothes indoors
- Breathing
Without adequate ventilation, humidity continues rising.
The moisture then settles on the coldest surfaces in the room.
Behind curtains, there is often very little airflow to help dry these surfaces.
🪟 Are The Windows Faulty?
Usually not.
Many people assume condensation means the windows have failed.
In reality, condensation is often a sign that:
- Indoor humidity is too high.
- Ventilation is insufficient.
- The surrounding surfaces are too cold.
Even modern double-glazed windows can experience condensation if humidity levels remain elevated.
🌧️ Could It Be Penetrating Damp?
Sometimes, but less commonly.
If mould is accompanied by:
- Damp patches beneath the window
- Bubbling plaster
- Water staining after rainfall
- Damaged external pointing
- Failed window sealants
then rainwater ingress may also be contributing.
A professional inspection helps distinguish between condensation and penetrating damp.
⚠️ Signs To Look Out For
If mould is developing behind your curtains, you may also notice:
✔ Condensation on the glass every morning
✔ Black mould around window frames
✔ Damp window sills
✔ Musty smells
✔ Peeling paint
✔ Bubbling wallpaper
These are often signs that moisture is remaining around the window for too long.
🔍 How We Diagnose Hidden Mould
At Weather Wise Solutions Limited, we assess:
- Relative humidity
- Ventilation performance
- Window detailing
- Thermal bridging
- External wall condition
- Moisture patterns
Because the important question isn't:
👉 "How do we remove the mould?"
It's:
👉 "Why is moisture collecting behind the curtains?"
🛠️ How We Resolve Mould Behind Curtains
The right solution depends on the underlying cause.
Recommendations may include:
- Improving ventilation
- Installing Positive Input Ventilation (PIV)
- Upgrading extractor fans
- Managing indoor humidity
- Repairing failed sealants
- Repairing external defects
- Installing insulation plaster systems where appropriate
Removing the mould without addressing the moisture will usually result in it returning.
👨🔧 Preventing Mould Behind Curtains
Simple changes can make a significant difference:
✔ Leave a small gap between curtains and the window sill.
✔ Open curtains during the day to improve airflow.
✔ Use extractor fans when cooking and showering.
✔ Keep trickle vents open where fitted.
✔ Maintain a steady indoor temperature.
✔ Avoid drying clothes indoors where possible.
These small habits help reduce condensation and keep the area behind your curtains drier.
📞 Need Help in Preston?
If you're finding black mould behind your curtains or around your windows, it's worth identifying the underlying cause before the problem spreads.
At Weather Wise Solutions Limited, we're a family-run damp company specialising in:
- Mould and condensation control
- Ventilation solutions
- Damp proofing
- Penetrating damp diagnosis
- Indoor air quality assessments
We're proud members of the Damp Proofing Association and the Federation of Damp, with surveyors holding the City & Guilds-recognised Federation of Damp Certified Surveyor (FODCS) qualification.
👉 Book your free quote here: https://weatherwiseuk.co.uk/pages/contact
👉 Contact us today: https://weatherwiseuk.co.uk/pages/contact