Why Do Windows Condense? What Each Location Means

Cooking, bathing, drying clothes and breathing add water vapour to indoor air. When the glass or frame surface falls below the dew point, that vapour becomes droplets. Lowering humidity or raising surface temperature changes the balance.

Persistent water at reveals can also indicate a cold bridge or air leakage around the installation. Wipe standing water promptly, record the room humidity and check whether the pattern follows the glass edge, frame or wall junction.

On clear, still mornings, the outer pane of a well-insulated unit can cool below the outdoor dew point because little room heat reaches it. Moisture may form outside and disappear after the sun or air temperature rises.

This temporary external misting is different from leakage. It is most common on exposed glass with an open view of the sky and does not normally require a repair.

A sealed insulating glass unit should keep its cavities dry. Haze or droplets that cannot be touched from either side may mean the edge seal has failed and moisture has entered the unit.

Cleaning and ventilation cannot remove moisture trapped in the cavity. Record the glass marking and contact the supplier or service team to confirm whether the glazing unit can be replaced within the existing sash.

Use extraction during cooking and bathing, keep air paths open between rooms and operate mechanical ventilation as designed. Short, effective purge ventilation is generally preferable to leaving a window slightly open for many hours in cold weather.

Avoid blocking radiators and vents with heavy curtains or furniture. A hygrometer helps relate symptoms to actual relative humidity instead of guessing from how the room feels.

Arrange an inspection if there is water between panes, draught at the gasket, visible mould at one junction, damaged seals or recurring moisture despite controlled indoor humidity. The cause may be glazing, adjustment, ventilation or the wall connection.

LUPOL can assess timber and uPVC window symptoms and advise whether adjustment, glass replacement, installation repair or complete replacement is proportionate. Avoid sealing intentional drainage or ventilation openings as a DIY cure.