Typical signs
- Fogging or droplets on glazing or frames.
- Local blackening at corners, damp curtains or peeling paint at the perimeter.
- Seasonal condensation that is worse at night or in deep cold.
Where it is often found
- Bedrooms, bathrooms, kitchens, basements and rooms with blinds kept closed.
What it can mean
- Indoor humidity too high for the season.
- Low-performing window, thermal bridge or poor fit.
- Insufficient ventilation or blocked airflow in front of the glass.
What to check next
- Compare relative humidity with outdoor temperature.
- Check exhaust fans, HRV/ERV operation and clear grilles.
- See whether fogging is between panes, which can indicate seal failure.
Reasonable immediate actions
- Reduce moisture sources and increase extraction/ventilation.
- Pull bulky furniture back and open blinds or curtains slightly.
When to stop and call a professional
- Condensation inside an insulated glazing unit, frame rot, liquid water entry or significant mould.
Prevention
- Match indoor humidity to season, ventilate kitchens and bathrooms, maintain weatherseals and caulking.