Secondary Glazing for Condensation Control
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?
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.
What are the Causes of 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 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
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
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
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!
Secondary Glazing for Condensation Control
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
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
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
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.
Severe Condensation Problems, Condensation & Dampness – includes advice on removing condensation mould growth and preventing its’ reoccurrence
And Finally - Some “Picture Tips” about Condensation & Dampness
- how to recognize the difference
- how to avoid it
- what to do about it if you have it