Surface condensation

A practical comparison of weather, water-use and temperature patterns. This renewed guide explains what to document, which competing pathways remain plausible, where ordinary self-help should stop and how to verify the outcome.

Water on the interior surface forms when humid indoor air reaches glass below its dew point.

The pane surface and whether moisture can be wiped away provide the decisive clue.

Compare liquid water entry with vapor condensing on a cold surface.

Warm humid outdoor air enters and reaches surfaces cooled by ground contact or air conditioning.

Indoor moisture meets cold glass, collects at edges and can wet seals, frames and nearby finishes.

A localized brown or yellow mark can reflect active water entry, an old dry stain or repeated condensation.