The moisture that suddenly appears in cold weather on the interior or exterior of window and patio door glass can block the view, drip on the floor or freeze on the glass. It can be an annoying problem. While it may seem natural to blame the windows or doors, interior condensation is really an indication of excess humidity in the home. Exterior condensation, on the other hand, is a form of dew — the glass simply provides a surface on which the moisture can condense.