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Double Glazing Condensation problems in UPVC windows

Double Glazing condensation problems in uPVC windows, answered here with a comprehensive explanation and helpful advice. By David our expert Window Wizard.

Misted windows and double glazed condensation, is a common problem. We have received a lot of inquiries from customers regarding, condensation problems.

There are 2 very different types and causes, of condensation problems in uPVC windows. However, they are not to be confused, as solutions are completely different. I hope that our explanation will help you identify which type of condensation problem you have and how to fix it.

If you require a quote for new double or triple glazing windows Click Here.


What is Condensation?

Condensation consists of small drops of water which form when warm water vapour or steam touches a cold surface such as the glass in windows. This is a result of hot air or steam becoming cool.


Condensation problem 1: Condensation in between the double glazed, glass sealed unit.

This type of condensation you can see but not actually touch the water or condensation with your finger. Please see the picture as shown below, illustrating water and condensation between the glass.

The primary reasons for condensation between the glass is due to old age, typically over 10 years old. Or if the unit has been badly fitted such as a screw head, packing wedge has pierced the edge of the unit.

Furthermore, double glazed units that are south facing so extra exposed to the sun, are less durable than double glazed units that are not in direct sunlight.

Condensation within the glass can also occur, when the glue of the joining strip which holds the 2 pieces of glass together has broken down, this allows moisture to penetrate between the glass panes.

This type of double glazed condensation problem is a simple and easy fix. This can be solved by replacing the glass sealed unit.

Condensation Problem 2: Condensation appearing on the inside of the windows/glass.

This type of condensation you can touch and feel the water with your finger. Please see the picture as shown below, illustrating water and condensation on the glass.

Most times condensation within the room is NOT caused by a window issue but a damp problem or lack of airflow.

What causes Double Glazed Condensation on the inside of the windows?

One reason for condensation on the inside of the glass could be lack of airflow in the room.

For example, if you shut your bedroom door and wake up in the morning with condensation running down your window glass, this is caused by lack of airflow.

Some double glazed windows have a facility where you can lock the window open in the vent position, this could help solve the problem.

Check your properties air bricks and vents. Ensure that they are not blocked and allow adequate airflow.

Or if you have recently had your loft insulated but not had vents fitted to the soffits or roof tiles. Also if your loft installation was fitted tight into eves, this can cause a damp and condensation issue as well.

Common causes of damp and double glazing condensation range from

  • Moisture i.e Body heat – shower/bath
  • Damp clothes on the radiators
  • Drying washing
  • Fish Tank (without a fitted lid)
  • Fireplaces blocked off without a vent fitted

Heavy curtains or blinds can reduce airflow and cause double glazing condensation issues, on the inside of your windows.

Another possibility could be that your property has a damp problem, in which case you would need a to contact a local timber and damp specialist. Who have the correct instruments for testing and finding the source of the moisture.

Do trickle vents fix condensation problems?

I am often asked to fit trickle vents into the windows but I am not keen on this idea as it very rarely solves the problem and causes most of the heating to flow out of the open vent plus increased noise from outside wind/traffic etc…

You can test this by leaving your small window open one inch and see if it cures the problem.

A list of Double Glazing Condensation Causes

  1. Lack of Airflow in the room, for example; air bricks blocked or room doors closed
  2. No ventilation in the loft area i.e loft insulation blocking soffits vents or no roof tile vents
  3. Leaky water pipes i.e heating pipes leaking under floorboards…
  4. Damp i.e underfloor air vents blocked or not a min of 6″ about outside ground level

Another solution is to install a dehumidifier however, they can be expensive to run. Also very noisy and require the water tank to be emptied regularly.

If you need to close your room door, why not fit a louvred vent into the door so air can still flow between rooms.

Effective and simple ways reduce condensation on the inside of your windows

  1. Check that there are no leaky water pipes, including radiators.
  2. Ultimately ensure you have good airflow, by leaving your internal doors open such as your bedroom door at night.
  3. If you prefer to sleep with the bedroom door closed, then perhaps fit a vent in the lower panel of the door which will allow airflow even when the door is shut.
  4. Windows can be locked in the vented position
  5. Heavy thick curtains could be preventing airflow, why not try living the curtains open to see if it solves the problem
  6. Check that your air bricks are not damaged or have been obstructed inside and outside.
  7. Check that you have either vents in your soffits or roof tiles

In addition, if the glue joining the 2 pieces of glass together, is penetrated or deteriorated due to old age. This will allow moisture to get between the glass panes and cause a condensation problem.

If you require a quote for new double or triple glazing windows Click Here.

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