How double or triple glazing helps reduce condensation on windows

As condensation only forms on surfaces cooler than the surrounding air, double or triple glazing can greatly reduce it by allowing the inner glass of windows to retain heat.

Cross section of double glazed and triple glazed windows

Energy efficient windows and condensation

Current Building Regulations specify that all new or replacement windows must meet minimum performance criteria. One method of meeting this requirement is to install energy efficient double or triple glazed windows.

For condensation to occur, a low glass surface temperature and high water vapour content in the air must be present.

What difference can double or triple glazing make?

Double or triple glazing and condensation

The basics: A warmer glass surface = less chance of condensation.

Double or triple glazed windows are designed to reduce the loss of heat from a room by conduction, from the inside to the outside of a building.

Under average conditions, and if a room is heated, the room side surface temperature of the inner pane of a double or triple glazed window will be much higher than with single glazing.

diagram of heat transfer through double glazed window

As a result, the likelihood of condensation occurring when warm, moist air in the room comes into contact with the glass is reduced.

The importance of adequate heating

Double or triple glazing can only work efficiently when there is sufficient heat within the room. When this is the case, it will greatly reduce the amount of heat loss through the window and as a result the room-side glass surfaces of the window will retain heat.

When rooms are poorly heated, double or triple glazing will not be able to reduce heat lost via conduction through a window. In this scenario, condensation may occur on the inside of windows regardless of the energy efficiency of the glazing (due to the low relative temperature of the glass surface).

The importance of adequate ventilation

Current regulations regarding replacing windows state that in regards to adequate ventilation, the situation should not be made worse than it currently is.

This means:

  • If there are trickle ventilators fitted in the existing windows, the new windows must also have vents that offer at least the same performance.
  • If there are no trickle ventilators in the existing windows, they are not required to be fitted to any new windows.

However a failure to have adequate ventilation in any heated room may result in condensation on other cold surfaces such as an un-insulated outside wall. For this reason it is important to consider ventilation requirements when replacing windows.

Why condensation occurs in unoccupied rooms

It is possible for condensation to occur in unoccupied rooms. This usually happens because such rooms aren’t heated and the inner surface temperature of window glass gets close to the outside temperature.

While the room may not have any active sources of water vapour generation, vapour generated elsewhere in the house can find its way into an unoccupied room. When it can’t escape it may then condense on the cooler glass of windows.

For more advice and information about reducing condensation in your home, get in touch with a local GGF Member company.

Related topics

Top tips on reducing condensation – room by room
What is condensation and why does it occur on windows?
Where condensation can form on a window and how to reduce it
Window condensation – where the water vapour comes from
A guide to home ventilation