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Condensation and roof window

Condensation is usually more noticeable on roof windows and flat roof windows because warm, moist air rises to the ceiling. We add more humidity to the air around us when breathing, perspiring, cooking, cleaning and showering. And this excess humidity condenses into water droplets on the windows.

What to look for

Wet mist on the inside of your windows may be the first warning sign that the air is too humid somewhere in your house. Even if your house doesn’t actually feel damp, that excess moisture could be doing damage in unseen places.

You can also look for:

  • Mildew on walls, window seals and baseboards
  • Peeling or bubbling paint
  • Deteriorating attic and wall insulation
  • Damaged floor tiles and deteriorating furniture
  • Rotting of structural wood between outside walls
Prevent excess moisture - help your house breathe
Condensation occurs more often during cooler weather because of the greater temperature difference between the warm inside and the cold outside. To fight condensation, you need to limit the amount of water vapour in your home, especially in the winter. Your home needs to breathe to fight condensation.
Condensation woman ventilation

You can do several things to ventilate your home:

  • Open a window in each room for a few minutes, two to three times daily to keep air circulating
  • Keep curtains, blinds and shades open, allowing warm air to circulate around the glass
  • Take shorter showers to limit indoor moisture
  • Cook with lids on your pots to reduce the moisture that is put into the air
  • Keep loft vents open to let the warm air out
  • Run kitchen and bathroom exhaust fans to expel hot moist air
  • Run ceiling fans to keep warm air from rising to the ceiling to help prevent condensation on roof windows and skylights
  • Make sure your clothes dryer and gas appliances properly vent moisture-laden air to the outside

Keep the water from condensing

If you are taking the proper precautions, but still experience condensation on your windows, it may be easier to remove unwanted moisture through ventilation or better insulated windows.

  • Install double-paned insulated windows and doors with energy efficient Low-E glazings. This helps to keep interior glass panes warmer.
  • Install vents below your windows to help warm the interior glass.
  • Run a dehumidifier during winter months and in damp weather.
Stop excess moisture

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How installing roof windows can help
Ventilation can quickly and efficiently remove condensation. That's why VELUX makes roof windows with several exclusive features that can help your house breathe.

They are easily opened

VELUX roof windows can be opened with manual or electric controls to release the warm, moist air trapped in your home.

Wood sash and frame add insulation

All VELUX roof windows are constructed with quality wood. Unlike metal or vinyl, wood is an excellent natural insulator because it does not conduct heat.

Energy efficient glass

VELUX roof windows are available with Low-E insulated glass. Low-E keeps the interior glass pane warmer and reduces the chance of condensation forming.

Maintenance tips

Before leaving the factory, all VELUX roof windows are treated with a water-based fungicide and bactericide. After installation, they should be given further coats of good quality paint or varnish at regular intervals. If, however, condensation has been a problem, some discolouration or mould growth may have occurred, and although the strength of the timber is unaffected, the result can be unsightly.
Removing wood mildew
Mildew on a wooden window frame indicates there is an issue with too much water vapour in the air and too little ventilation. Besides being unsightly, the mildew can inflict damage on the wood. It also contains spores that can get into your body and result in discomfort and health issues. Therefore, removing mildew is vital if you want a healthy indoor climate and window frames that last for many years. Follow these easy steps to get rid of the mildew.

Step 1

The mould must be killed using a sterilising agent. Scrape off any surface mould, then clean the area with a solution of one part household bleach diluted in 10 parts water.

Step 2

Rinse well with clean water. When thoroughly dry, rub down wood with medium sandpaper. Repeat steps 1 and 2 until the mould is removed.

Step 3

Finally, coat with a proprietary clear wood preservative and then finish with paint or varnish as desired. 
How to use your roof windows during the winter
In snowy weather, the ventilation flap should be kept closed. If the ventilation flap is open, the warm air inside will flow out and melt the snow above the roof window. The melted snow will freeze on the window covers and make the window difficult to open. If you want to air the room, the window must only be opened briefly. Even without snow on the roof, water may drip from an open ventilation flap in cold periods. This may happen when warm, moist air inside the building meets extremely cold fresh air. In these situations, the ventilation flap should be kept closed. If you want to air the room, you can open the window for several minutes.

Why do new houses often have condensation issues?

Condensation is more prevalent in new homes. After a few years, new homes tend to dry out and have less moisture problems. Eliminating excess moisture by using a dehumidifier and providing adequate ventilation and air circulation will go a long way in preventing condensation.

Installing roofing underlay between the roof window frame and roofing material will also help prevent condensation on the cladding.

When a leak isn't a leak!

Condensation can form on more than just glass. In some cases, the installer neglects to use roofing felt and insulation between the frame of the unit and the rough opening. 

This allows warm, moist air to escape from the room and come into contact with the underside of the flashing and/or cladding. 

The resulting condensation will drip back into the room between the frame and roof opening, giving the appearance of a leak. Having the roofer or installer add felt and insulation between the frame and roof opening should prevent this problem.