It's that time of year again when cold night temperatures offer the optimum conditions for condensation to form on the external surface of double-glazed windows.
High-performance windows and glazing now insulate the home far better than older windows and single glazing. This keeps the heat within the room and reduces loss through glazing. This means the outer pane is no longer heated by heat escaping from the home. Therefore, this outer surface is much more relaxed, and if the conditions are appropriate - cold temperature and atmospheric moisture- condensation can form on this outer pane surface.
Whilst this can raise concerns for homeowners, it is normal and a good indication that the windows are performing correctly. Just as snow will remain longer on insulated loft roofs, condensation can form on better-performing windows.
Once the sun comes up and temperatures rise or if there is a breeze, this condensation will evaporate and disappear.
External condensation can often exhibit patterns and marks that cannot be seen when the window is dry. These patterns may be label marks, crisscross lines from our toughening plant (picture below), protection pad marks, etc. All these, in effect, repel moisture and often show up within the condensation both outside and inside the home.
Although homeowners may be alarmed by condensation and patterns, this is normal and does not represent any fault with the glass. Visual standards state that glass should be inspected when dry and clean. Under these terms, condensation is not present, and no patterns/marks can be seen.
