Why it appears
Condensation appears when humid air touches a cold surface. It may occur on glass, frames, shutter boxes or around the opening if there are thermal bridges or poor ventilation.
It is not always the window’s fault
New airtight windows reduce draughts but can reveal insufficient ventilation. Cooking, showers and drying clothes indoors increase humidity.
What efficient windows improve
Good frames, low-e glazing, thermal break in aluminium and proper sealing reduce cold zones, but ventilation remains essential.
What to check at home
Monitor humidity, ventilate briefly, review shutter boxes and wall junctions. Condensation inside the glazing unit may indicate a failed sealed unit.
What to request in the quote
Ask for suitable glass, thermal treatment, shutter-box solution, perimeter sealing and how thermal bridges will be handled.