Condensation on the Outside of Double Glazing

Today’s modern double glazed windows come with very well insulated frames that are designed to be as energy efficient as possible.  This energy efficiency has come about through changes in Building Regulations and government commitment over recent years to reduce the carbon footprint generally as well as heat loss through our homes. However one unintended consequence of these improvements is the possibility of Condensation on the Outside of Double Glazing.

The Casement window is by far the most popular type of window used in typical British homes today.
Modern double glazing is very sophisticated in keeping heat in the home and cold out.

Therefore if you are purchasing new windows today, whether in aluminium, pvcu or timber, you can be assured that they will all meet the latest window energy ratings and current standards for thermal efficiency.

What is it that makes windows thermally efficient?

With aluminium windows this insulation is achieved by a sophisticated material called polyamide that creates thermally broken windows. 

In pvcu windows it is the multi chamber design within the frame that creates an insulated frame.  In timber windows, the solid nature of wood also acts as a great insulator.

The insulated frames available in aluminium, pvcu or timber windows are also complemented by very high specification double glazed units.  When double glazing first came about, the two panes of glass were simply standard glass with a hermetic seal around the double glazed unit and a normal air space in between.

Glass technology has now advanced significantly and your glass will now comprise either a Low Emissivity (low E) coating, K Glass and further enhanced by argon gas between the two panes of glass and a warm edge spacer bar that is far superior than the standard plastic or aluminium spacer bar that held the sealed unit together.

Modern replacement windows ensure heat is kept in and cold kept out.

So you can be confident that today’s energy efficient A, B or C rated and highly secure windows will help to retain heat in the home and keep the cold out.  One phenomenon that cannot be avoided is the presence of condensation and particularly on the outside face of your new windows.

If you do see condensation on the outside pane of your new windows, do not be concerned, the windows are simply doing their job. In simple terms you will see surface condensation where the temperature on the external pane of glass is lower than the temperature outside or where there external temperature is higher than the temperature of the glass.

The presence of Condensation on the Outside of Double Glazing is not a sign of a faulty window or glass.

But if you do see condensation between the two panes of glass on the inside of the sealed unit, this indicates that your double glazed unit has failed and needs replacement.  In most cases the hermetic seal that bonds the unit together and seals it will have failed, letting in air and moisture.

The presence of condensation on the inside of double glazed windows is not a fault but in many cases just a consequence of how we live.

What should you do if you see condensation on the outside of your window?

At certain times of the year, you will see condensation on the outside of your window.  This is a similar phenomenon to your car having condensation on seemingly dry nights or when only certain parts of your car are wet and others are dry.  Moisture will adhere itself to the first cold surface it finds.  The double glazed windows are actually doing their job of keeping the heat in and the cold out.

In most cases the condensation may only be visible on the centre area of your window rather than the edges where glass meets the frame. This again is a sign that the window is performing as it should be.  The condensation will disappear as the external temperature increases during the day.

 Should you be told about condensation before you sign up for new windows?

That will depend on your salesman.  The experience and knowledge of double glazing salespeople varies significantly from company to company.  You will find that many of the independent local double glazing firms will probably adopt a more professional approach to this issue.

Other national companies employing commission only salespeople keen to close a sale on the night are unlikely to highlight any kind of “negative” with their product and will choose to say nothing.

If you need further impartial and independent information about condensation on new windows or any other aspect of buying replacement windows, please contact us using the form below.
Have you started noticing condensation on your double glazed windows?  Double glazing condensation can occur the outside pane of glass or elsewhere on the window.  Naturally this can be alarming, particularly if the windows or doors are new, but it is not necessarily something to be concerned about.

Failed double glazed units will demonstrate condensation between the panes of glass.
There are many factors causing condensation but double glazing will never eliminate it.

Where new double glazed windows have replaced old single glazed windows such as old Crittall Steel windows or single glazed timber windows you may be  surprised at the presence of condensation.  After all, double glazing is supposed to eliminate condensation isn’t it?

The presence of condensation may also be particularly evident in the Autumn. But why is this, what is condensation and should your new aluminium double glazed windows even be allowing double glazed condensation in the first place?

Should new windows suffer from double glazing condensation?

Firstly, it is important to understand that all windows will condensate in some way.  You must never believe any double glazing salesperson that says “our windows will eliminate condensation”. This is untrue and completely misleading. New windows can never completely eliminate condensation.

What new double glazing will do is improve the current level of condensation on your old windows.  This is because the thermal properties of modern aluminium frames and the high specification of modern double or triple glazing will be far superior than single glazed windows and non insulated frames.  All the modern aspects of today’s windows  play a part in reducing condensation but nothing can eliminate it.

The presence of condensation is down to several factors but the main ones are how we live in our homes and what we do that causes moisture in the air.

Modern buildings are now very well insulated both in their construction and of course windows.  In older buildings that are less well insulated air flow changes are more frequent.  In modern buildings the water vapour that causes condensation is unable to escape through old windows, chimneys or the structure and has to settle on the first cold surface. This will often be the windows but can also be on bathroom tiles or walls.

Water vapour is the cause of condensation.

It is modern life and the advances in construction products that all play a part in causing condensation in the home.  Here are some common cause of double glazing condensation:

  • Simple cooking and the steam generated from pots on on the stove all generate water vapour.
  • New build properties contain a huge amount of moisture until they dry out completely.  Consider how exposed to the elements the building was during its construction and until it was sealed by the roof or windows.  Over 6000 litres of water are estimated to have been absorbed by a typical dwelling during its construction.
  • Heaters are also a cause of moisture in the air.
  • Breathing whilst we sleep is well known to produce several litres of water vapour during the night.
  • Drying washing indoors are also significant sources of water.

What benefits have double glazed windows brought to the improvement of condensation?

Single glass found in old single glazed windows simply cannot retain any heat.  As the glass has a lower temperature this lets moisture in the air condensate on the cold surface.  This is why single glazed windows condensate.

By comparison, double glazed windows offer two pieces of glass and therefore retain the heat inside the room.  Old double glazed units were simply two pieces of glass with an air space.

These still let out some heat but performed better than single glass.  Modern double glazing with sophisticated glass coating technology, high specification sealants and spacer bars and the presence of argon gas between the two pieces of glass all substantially reduce the loss of heat from inside the room.

Therefore the presence of condensation is unavoidable in our dwellings but there are of course steps you can take through adequate ventilation to reduce it as much as possible.

What to check for when your double glazed windows have condensation:

So, hopefully you can now see that there is always the possibility of some condensation forming on double glazed windows.  Condensation on the outside of double glazed windows is nothing to worry about, as is condensation on the inside of the window.  However, if the glass inside the window is misting up or showing signs of moisture then the window may be failing and should be investigated as a matter of urgency.

Condensation on the inside of your windows may be a sign that there is excessive moisture in the air, aside from the inconvenience of having condensation, you should consider what effect this could have on the plaster work and wood in your home.  Ensuring that there is plenty of ventilation flowing through your home is good for the building and your general health!


Published on October 12, 2014

Reader Interactions


  1. Michael Carter says

    So technology has now moved on and we have produced a window you can’t see through? Surely the main purpose of a window is to be able to see through it. If thermal efficiency was the main aim I would have an insulated brick wall.
    I have never heard of anything so ridiculous in all my life fancy having wonderful views, waking up in the morning and not be able to see them because the new windows have misted up. Absolutely ridiculous and infuriating if you have just paid for new windows.

    • Nick Dardalis says

      It’s as much to do with natural occurrences as it is to do with technology Michael – the effect of a cold surface one side and warm surface the other. Condensation is better on the outside of my property than the inside!

  2. Robert Hobkirk says

    Dear Sir madam,

    Am I more likely to get condensation on AL windows as opposed to Wood and or PVC, or its soley down to the U value, and how does AL, U values compared t that of Wood?

    Kind regards,


    • Nick Dardalis says

      Hi Robert, wood windows have some of the best insulation of any aluminium or PVCu window and the frames are the best for insulation. Condensation happens for many reasons and often the windows are not the cause. The Glass and Glazing Federation has some excellent advice about condensation that may help you too.

      No window completely eliminates condensation and the choice of glass is another factor.