Water vapour condensation on the window glass.

Water vapour condensation on the roof window pane is a frequent problem in autumn and winter. See why this phenomenon occurs and how to prevent it.

Condensation of water vapour on the pane is not a rare phenomenon; it occurs where there is too high a level of humidity in the room. However, the moisture in the house itself will not yet cause water to condense – a massive difference between the air temperature inside and outside the building is needed. Therefore, the most concerned about the phenomenon of condensation of water vapour on the windows (because the water vapour condenses in the coldest place). There are a lot of requests to the services dealing with the installation of windows in autumn and winter.

A roof window is an “ideal” place for water accumulation and condensation. Warm air wanders up the room and meets the coldest element there – the roof window pane. People who have such skylights know that even when it is difficult to see traces of moisture on other windows, they often occur on roof windows. It is enough that the difference between the air temperature inside and outside the room exceeds 20 degrees Celsius and the humidity in the flat will increase up to 60% for water drops to appear on window panes.

Ventilation in the attic

When should you not worry about moisture on your roof window?

The element that affects the accumulation and condensation of steam on the windows is the daily activities. The most significant “chance” for steamed up roof windows is when meals are being prepared in the kitchen, or the owners… or the owners of the roof window are cleaning the floor.
It is worth noting; however, that roof windows in individual rooms get naturally damp in away. This is the case in bathrooms, for example. If water collects on the window after bathing but disappears after a long time, there is no reason to worry. The same is true when there is a sudden cooling outside the building.

As a rule, recently completed flats have high humidity, as well as renovated rooms. “Breathable” walls, primers, mudding compounds – they will evaporate for weeks, and moisture will collect on windows very often.

Moisture on the window – a severe warning

Condensation of water vapour on roof windows is dangerous when it occurs systematically. This phenomenon should be a signal to residents that ventilation in their homes is inefficient. And it should be emphasised that too high air humidity in the house, which is indicated by a steam on the windows, has severe consequences for the household members.

Tolerating humidity is an invitation to the interior of fungi and moulds, which most often start their invasion around vaporised roof windows. Their appearance also means an unpleasant ‘basement’ smell in the flat and the danger of illness and allergy when mould spores appear in the air. Therefore, the signals of accumulated moisture on the windows should not be underestimated.

It is important that the humidity in the interior of the room remains at the level of about 50%. Sometimes it is just enough to ventilate the house more often. Slightly unsealing the window should also help to ensure proper micro ventilation, but ventilators are much more effective.

Roof window ventilators instead of open windows

Opening windows in winter have its disadvantages. Especially where thermal comfort is difficult to achieve, ventilation causes considerable energy losses and the necessity to obtain the expected temperature inside the flat for longer. Therefore, already at the stage of window replacement, it is worth taking care to have a ventilation system (optilight version VB) or micro-opening system.

A convenient solution also handles with a locking cube with a two-stage ear. They allow the air supply and at the same time, the window remains closed.

In autumn and winter, you should remember about regular cleaning, de-icing and snow removal of your roof window. It may happen that as a result of snowfall, the drainage elements will be clogged and the snow will settle on the roof window instead of flowing down.

Finishing the window recess

Whether or not water vapour accumulates on the roof window is also influenced by the finish of the window recess – it is about ensuring efficient air circulation around the window. That is why the so-called “slugs” (window niche trim elements) should be properly positioned. The lower one must be perpendicular to the floor, and the upper one parallels to it.

Additionally, it is worthwhile to install a radiator under a roof window. Warm air rising from it will dry the window. However, it should be remembered that if we do not follow these recommendations or use a window sill under a roof window, the air circulation will not be sufficient, which may cause condensation.

Make sure that the window is warmed up around it.

Moisture problems around the window may also result from the lack of proper insulation around the roof window. This results in large temperature differences, which are conducive to condensation of water vapour. Therefore, already at the window installation stage, it is necessary to take care of all insulation layers – i.e. the vapour barrier on the room side, the thermal insulation and the vapour-permeable layer on the outside.

At present, window manufacturers offer ready-made installation kits, which facilitate the proper execution of insulation around the roof window.

If not moisture – manufacturing or installation defects of the window

Sometimes condensation of water vapour does not result from poor ventilation in the house, and the responsibility for this phenomenon are window installation errors or manufacturing defects. Such a suspicion occurs when, next to water condensation, frost is visible on the window – which appears when the so-called thermal bridges are formed, which are usually the result of breaking the window insulation layer. The situation is similar when water accumulates on the inside of the window. This is a visible sign of a malfunctioning window. In this situation, either replace the inner pane or, if this is impossible, install a new roof window.