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Sound Proofing Thermal Insulation Condensation Control Added Security



Secondary Glazing for Condensation

What Causes Condensation?

The simple answer is - airborne moisture coming into contact with a cooler surface - this causes the airborne moisture, if the air is saturated, to condense onto the coolest surface in your house - the first result is usually condensation on windows.

In practice, though, home condensation problems are often elusive!


They are generally caused by a combination of very local, varying factors - and they can be incredibly frustrating to deal with & eradicate at times:


  • Why does one property have condensation problems and not another, similar, property?
  • Why do one or two rooms within a property attract condensation and not others?






The answer to these questions is more complicated!

Window Condensation

Air & Airborne Moisture

Air is the word we use to describe the atmosphere around us.


It is made up of a mixture of gases - composed roughly as follows:


Nitrogen        78%

Oxygen          21%

Other Gases    1% - Argon, Carbon Dioxide, Methane, Neon, Helium, Krypton, Hydrogen & Zenon


Air also contains (or carries with it) minute solid particles, which we commonly refer to as pollution.


Additionally, air always carries with it varying amounts of moisture, in the form of water vapour.


Outside, the amount will depend upon the day – hot, cold, warm, sunny, rainy, dry, humid, etc.


Inside, the amount will depend upon what it’s like outside plus what we are doing to keep ourselves comfortable inside if it is cold - plus anything else that we are doing that adds water vapour to the air.

Gas Composition of the Atmosphere



"Just breathing is a major problem!"



“One person simply breathing adds nearly half a pint of water vapour to the air every hour!”



"A couple, sleeping the average 8 hours, will produce 8 pints during the night!"

Simply Breathing Causes Condensation!

Add to that items such as cooking, bathing, washing and drying clothes. Hover over the pictures below to see how much moisture each activity adds to the air inside your home:

Cooking a Main Meal for a Family of Four on a Gas Cooker Adds Around 3/4 of a Pint A Quick Shower Adds Nearly 1/2 a Pint
The Weekly Wash for a Family of Four - 4 pints! Drying Those Clothes Indoors, Either Naturally or in an Unvented Dryer - Over 3 Gallons!!!!

Add to the above doing the washing up and mopping the floor and it soon becomes apparent that we are adding dramatically to the water vapour in the air.


Therefore, we are also adding to the possibility of home condensation problems, especially condensation on the windows, which are usually the coldest suitable surface in a room.

Saturated Air

The warmer the air, the more water vapour it can hold - conversely - the cooler it is, the less water vapour it can hold.


When the air in your house becomes colder, it cannot hold all the water vapour that it has previously absorbed.


When it reaches the temperature at which it cannot hold any more water vapour - it becomes, quite literally, saturated.


This is known as the - “Dew Point.”


Any further drop in the temperature inside your home results in the air expelling the excess water vapour in the form of condensation.


The condensation will form on any cooler, impervious surfaces, such as:

  • Windows
  • Mirrors
  • Painted woodwork
  • Cold spots such as the corners of rooms
  • North facing external walls

Most frequently, you will experience window condensation, firstly condensation on the glass and then, depending upon the severity of the problem and the type of window, on the frames, the internal sill & around the window reveals, surrounding wall area & especially below the window.

Condensation Damage


The real key to all of this is - humidity - the balance of moisture in the air.


In cold weather we reduce ventilation to keep the warmth in, thereby reducing the natural cycle of ventilation which allows moisture laden, humid air, to “escape” from the property and be exchanged for drier, less humid air from outside.

The result - the “trapped,” humid air, reaches dew point & the inevitable, unavoidable result, is that it expels the excess humidity, or moisture, which then forms as condensation on any available, cool surfaces.


NB - the facts are - the higher the humidity, the higher the temperature needs to be in order to prevent condensation from forming on cool surfaces.


It is, however, virtually impossible to maintain a comfortable indoor temperature combined with a high humidity level &  reduced ventilation - without condensation forming!

Ambient Temperature - Humidity - Dew Points

So having identified the major cause of condensation as humidity, how do we resolve it?


The only solutions are ventilation and controlling the amount of moisture that we produce.


These are both dealt with in detail in the control, reduce & eliminate condensation section.

Condensation & Double Glazing


Condensation problems are not isolated to single glazed windows - in fact condensation inside of double glazing is a frequent problem due to a lack of ventilation.


  • We regularly install secondary glazing for condensation inside double glazing!


If  your problem is much more severe or complicated, please also consult the severe condensation problems, condensation & dampness page.

Condensation on Inner Glass of a Double Glazed Window


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