Cricklewood Glass - Quality Products & Services Since 1986

Now At Larger Premises: Unit 6d, Atlas Business Centre, Oxgate Lane, London, NW2 7HJ

Glass - Glazing - Secondary Glazing - Soundproof Windows - Splashbacks & Worktops -  Double Glazing & Units - Mirrors - Table Tops - In fact, Everything Glass!

Secondary Glazing for Condensation on Windows - Control, Reduce & Eliminate Condensation



Secondary Glazing for Condensation Control

Condensation on Windows, Secondary Glazing London

We have been helping people deal with condensation control for many years and it can be a complicated problem - understanding the causes properly is often half the battle!

Our extensive research into the problem of general condensation and particularly condensation on windows, is presented in the following sections, where we discuss it in detail.

We apologize in advance for the length of this page!

At the bottom of the page you will also find some helpful downloads and pictures.

Condensation is Normal!

  • it occurs whenever moist, warm air, encounters a cold surface
  • it is most common during the coolest, dampest months of the year
  • particularly from October through to April

What can be considered Normal Condensation?

Single Glazed Window Condensation is Normal

Virtually every property gets condensation at some time - usually when it is cold and damp outside, the heating is on & lots of steam & moisture are being produced inside - such as bath times or when washing clothes and cooking meals.

Normal condensation occurs because the material structure of your home is naturally cool and because there is insufficient ventilation to allow the moist warm air inside to escape.

Put bluntly - it occurs because of our natural tendency to want to be as comfortable as possible inside - whenever it is cold outside:

  • we turn the heating up
  • close all the windows & doors
  • & do anything else that we can to stop the draughts

The result - airborne moisture cannot escape & therefore condenses on the coldest surfaces, usually & firstly resulting in window condensation on the glass, around the windows and on the lower parts of the external walls.

Condensation on the lower parts of walls is easily confused with rising damp - we deal with this below.

Bathing - Produces Condensation, Secondary Glazing London
Washing - Causes Condensation, Secondary Glazing London
Cooking - Creates Condensation, Secondary Glazing London

What are the Causes of Condensation?

Person Breathing, Adds Nearly Half a Pint of Water to Air Every Hour, Secondary Glazing London

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 window condensation.

These are the major causes of condensation:

  • when it’s cold outside and warm inside
  • high inside humidity - followed by a fall in temperature - the air expels water as condensation
  • activities such as bathing, washing and drying laundry, and cooking
  • one person simply breathing adds nearly ½ a pint of water vapour to the air every hour!
  • insufficient ventilation - a modern property needs a complete air change every 2 hours - older properties need a complete air change every hour! So, shutting up everything tight is guaranteed to cause condensation. Controlled ventilation is a must!
  • the building research establishment reports that - “80-85% of dampness problems arise due to man-made moisture and condensation.”

What Causes Condensation on Windows

It is Normal for Condensation to Occur Predominantly on the Windows, Secondary Glazing London

During cold, damp weather - windows provide the ideal surface for condensation to form, they are usually the coldest surface in a room, therefore:

  • when warm air passes over the cold glass, the air cools
  • as the air cools, it becomes saturated & reaches “dew point”
  • the cooler air can no longer hold its’ excess water vapour
  • the excess water vapour is expelled & forms as condensation on the glass

Hot air rises, cold air falls!

The air, now cooled by passing across the cold glass:

  • then naturally drops downwards
  • this creates a convection current
  • which pulls more warm air from above the window across the cold glass
  • depositing more condensation - on & often below the window
  • and also causing cold drafts

This creates a vicious circle, which is what causes the condensation on windows!

Condensation on Bedroom Windows

Morning Condensation on Double Glazed Bedroom Window Secondary Glazing London

Bedroom windows are especially prone to condensation.

We tend to have the heating set lower or turned off during the night.

The air gradually cools and sets off the condensation cycle described above.

Additionally, as previously stated, each of us:

  • adds nearly ½ a pint of water vapour to the air every hour breathing during the night

As can be seen on the image here, condensation on bedroom windows is not isolated to old 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!

After installation, customers often comment that apart from resolving the condensation problem, their bedrooms are both warmer during the winter and significantly quieter all year round!

How to Control, Reduce & Eliminate Condensation

Secondary Window over Modern Double Glazing Stops Condensation being Caused by the River, Secondary Glazing London

The critical factors in condensation control are:

  • good insulation
  • controlling the production of excessive moisture
  • keeping humidity levels in check
  • sufficient balanced ventilation
  • reasonable but not excessive heating

These factors must be properly balanced!

How to Control, Reduce & Eliminate Condensation pdf

Secondary Glazing for Condensation Control

Balanced Ventilation in the Secondary Glazing Cavity Prevents Condensation

The best solution specifically for window condensation, is secondary glazing.

Good quality, well fitted, secondary windows, with unsealed primary windows or trickle vents, provide a complete, tight, internal seal and:

  • allows balanced, low level ventilation within the window reveal cavities
  • stops the inner glass from becoming too cold
  • prevents condensation forming on both the primary & secondary windows
  • protects the primary windows from condensation damage

Additionally, the added insulation:

  • prevents the heat, which you are paying for, from escaping too quickly
  • allows background ventilation within the property time to clear excess water vapour from the air
  • helps to prevent condensation forming elsewhere

Treatment of the Existing Windows when Installing Secondary Glazing

Where the Existing Primary Window is Very Well Sealed, Cavity Should be Ventilated, Secondary Glazing London

When fitting secondary glazing, the existing windows:

  • should not be sealed up or fitted with draught excluders
  • it makes very little difference to the overall thermal & noise insulation
  • doing so can create a condensation trap within the cavity

Where the existing primary windows are already double glazed or are very well sealed:

  • we recommend ventilating the cavity with a “trickle vent” in the frame at the top of the secondary window - to avoid creating a condensation trap

Condensation - Secondary Effects

Black Mould Growth and Damage Caused by Condensation on and around the Window, Secondary Glazing London

Apart from mopping up the condensation itself, especially in bedrooms, the secondary effects of condensation can include:

  • stained curtains
  • condensation stains below windows on wallpaper & other decorative finishes
  • the condensation runs & gets into the window frames via joints and seals
  • interior wooden window sills start to rot, often hidden beneath the paintwork
  • timber frames, especially around main frame, transom & mullion joints, start to rot
  • putty seals break down and start to bulge
  • paint starts to peel
  • black mould can form
  • metal (Crittall type) frames suffer rust spots & rust build up in the glazing channels
  • in extreme cases, in both timber & metal windows, glass can crack

All in all, window condensation can be very costly as well as very unsightly & inconvenient!

Severe Condensation Problems, Condensation & Dampness

Rising Damp 'Tide Mark,' Secondary Glazing London

Sometimes it is difficult to tell the difference, on walls, between condensation and rising or penetrating dampness.

As a rule of thumb, you can use the following guidance to differentiate:

  • rising and penetrating damp are generally caused by underlying structural defects
  • how can you tell?
  • condensation does not leave a 'tidemark' - rising and penetrating damp do

If you are not sure, or feel that your problem is much more severe or more complicated than just simple condensation, please consult the Severe Condensation Problems, Condensation & Dampness download below.


How to Control, Reduce & Eliminate Condensation pdf

Severe Condensation Problems, Condensation & Dampness pdf – includes advice on removing condensation mould growth and preventing its’ reoccurrence

And Finally - Some “Picture Tips” about Condensation & Dampness

Just hover over pictures to see:

  • how to recognize the difference
  • how to avoid it
  • what to do about it if you have it
Badly Positioned Radiators plus Draughts Create Convection Currents and Condensation on Windows
Balanced Heating Helps to Reduce Condensation
Blistered Paintwork Penetrating Damp
Blocked Downpipe Causing Lateral Damp Damage
Cold Spot Condensation Mould Growth
Condensation Damage Around Double Glazed Window
Condensation Mould Growth Around Double Glazed Window Frame
Condensation Mould on Internal Window Cill and Frame
Condensation Run Off Gets Into Joints Causing Wet Rot
Condensation Wardrobe Placed in a Cold Corner No Air Flow
Cover Pots and Pans to Stop Excess Moisture in the Air
Cracked Solid Floor Causes Damp and Increased Humidity
Damaged Brick Ties Causing Failed Mortar Lines and Allowing Water Ingress
Do Not Block Airbricks Essential for Balanced Ventilation
Double Glazed But with Severe Condensation Damage
Double Glazed Condensation Run Off Causing Damage to the Internal Cill and Side Plasterwork
Failed Perforated Lead Flashing
Faulty Replastering Trapping Moisture Caused This Damage
Fit Humidistat Fans to Kitchens Bathrooms and Problem Areas
Make Sure Clothes Dryers are Vented to the Outside
Mould Growth at Base of Wall No Tide Mark so it is Condensation not Damp
Mould Treatment Kits Available at Your Local DIY Store
New Extensions and Solid Floors Need Time to Dry Out
Penetrating Damp Damage
Rising Damp Caused by Faulty DPC
Slightly Open Windows for Background Ventilation
The Window is Double Glazed so the Condensation Forms on the Reveals
Very Cold Corner Severe Condensation Causing Mould Growth

Further information:

Download our Secondary Glazing Brochure pdf

Thank you for visiting - please Contact Us if we can be of any further help.