The right windows will help towards reducing condensation in the home

Modern living has often created much more habitable rooms, but also living spaces that are much warmer. However these changes can lead to less ventilation and fewer air changes. The result is that water vapour produced by normal living is no longer able to escape up the chimney or through door jambs, window joints and other outlets.

In fact, in certain circumstances, such material comforts can combine to create ideal conditions for the birthing of condensation, which tends to form on the coldest surfaces within any room. This may not necessarily be on the glazing.

Air inside a building contains a certain amount of water vapour, which generally increases for example when kettles are boiled, baths are run and if clothes are dried indoors. The volume of water vapour that the air can hold is a function of its temperature. Obviously warm air has the capacity to hold more moisture vapour than cool air. Therefore as the air circulates, and comes into contact with surfaces cooler than itself such as walls, woodwork and windows, the water vapour condenses, becoming liquid again. The steaming up of a bathroom mirror at shower time is a good example of how condensation droplets are formed; the mirror surface being cooler than the moisture-laden air. Whilst the condensed liquid will run-off glass or painted timber surfaces it is likely to soak into porous surfaces such as walls and ceilings.

Condensed water that soaks into walls or untreated woodwork will damage the underlying substrate of the building while simultaneously providing the perfect environment in which unpleasant and unhealthy mould colonies can grow. Many studies into the effects of inhaling mould spores unanimously agree that it causes damage to the immune system, skin rashes and respiratory disorders such as sinusitis and pneumonia

If home owners who have fitted energy rated replacement windows still experience condensation on the inside of their windows, it usually means that their property has a particular problem with condensation that they need to address through improving the balance between heating and ventilation. More often than not, these cases are caused by insufficient ventilation within certain rooms that need addressing, as new windows and doors are designed to retain heat, so if there is not enough ventilation then condensation can build up if warm moist air is trapped with nowhere to escape to. Such condensation can be reduced by leaving open window vents to allow fresh air in, or retro-fitting trickle ventilation (although these trickle vents can be expensive, ugly and defeat the object of fitting thermally efficient window products). Other solutions include adding air bricks, buying a de-humidifier or installing mechanical ventilation.

The Glass and Glazing Federation’s own publication about condensation on their website, entitled “Condensation, Some Causes, Some Advice” goes out of its way to make it clear that if condensation occurs on the outside of the external pane on double or triple glazed windows this is a positive sign that these thermally efficient replacement window products are in fact performing well. Such a phenomenon tends to only occur at certain times of the year, depending on a property’s location and aspect. Normally such condensation forms early morning and is gone by lunchtime.

As the GGF article on condensation advice for UK home owners states “Due to recent innovations in the efficiency of double and triple glazing, along with updated requirements of building regulations and the lowering of carbon emissions, certain weather conditions may allow the formation of external condensation on energy efficient windows and doors. This is a natural phenomenon and a clear indication that the window or door is preventing heat loss from your house.”

That said, condensation between the panes of glass in a double or triple glazed sealed unit means the unit has “blown” and is no longer providing the same level of thermal barrier that a modern high performance hermetically sealed unit can provide. Such blown units should be replaced ASAP, particularly in the colder months

When fitting replacement double glazing, homes with a known pre-existing internal condensation problem (e.g. which is quite common in blocks of flats) that need more permanent ventilation can have trickle vents built into the window’s or door’s outer frame. Modern double glazed replacement windows should offer a lockable night vent facility on all opening vents, which is a far better solution to condensation than trickle vents as the window can then be shut to keep out extreme cold if need be. The key factors in reducing condensation are having a) thermally broken, energy efficient windows and doors, b) sufficient heating, and c) enough ventilation.


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