External French doors are a great way to make your home feel brighter and more spacious. They create a seamless transition between your interior living area and your patio or garden. When fully open, they let in lots of light and fresh air and give you a wider open space to enjoy. When closed, they still allow light to flood into your living area, while offering the energy efficiency savings of double glazing – including both noise and thermal insulation.

You may notice, particularly in colder weather, that you get condensation on the inside of your French doors. We’ll look at what causes this, if it’s an issue and how to deal with it.

What Causes Condensation to Form on French Patio Doors?

Condensation on your external doors occurs when warm, humid air hits a surface that’s colder than the surrounding air – e.g. glazing or windows – causing the water in the air to ‘condense’ and form droplets. You can also get condensation on walls and ceilings.

To an extent, condensation is unavoidable, and is simply a natural process of warm air inside our homes interacting with cold glasswork. This is particularly evident in winter when the heating is on a lot and it’s cold outdoors. Nearly all homes will experience condensation on patio doors or windows and it generally isn’t something to worry about. Too much condensation which is left to sit on your doors can lead to damp and mildew though. Occasionally, condensation can be a sign of a larger problem.

Condensation On the Outside of Your Patio Doors

It’s very uncommon for condensation to appear on the outside of patio doors in this part of the world. That’s because condensation can only form on the exterior of windows when it’s very hot and humid outside, and significantly cooler inside – i.e. in hot climates and in properties with aircon.

Regardless, since the moisture sits on the outside of the windows, it won’t cause any problems, and can be left alone.

Condensation Inside Your Patio Doors

Condensation can form inside your home if you have poor ventilation, or if patio doors or windows are located near to, or in, a room that frequently gets steamy – like the bathroom or kitchen.

In this case, the hot air hits the cooler windows and condensation starts to form. This is why condensation is worse in winter, when windows are particularly cold.

If ignored, condensation can cause significant problems. We’ll talk about this more in a moment.

Condensation Between Patio Door Window Panes

Condensation inside double glazing is a big cause for concern. The panes of glass between double glazing are designed to be highly energy efficient, and should be completely sealed.

If condensation is forming between the panes, the seal between the two panes has been breached and the glazing will not be performing as it should be.

If you see water inside windows we advise contacting the manufacturer of the doors, or the company that supplied them as a repair or replacement will be necessary.

Condensation and New Build Homes

Newer properties naturally contain a lot of water. A new build can have as much as 1500 gallons of liquid in it, because of the moisture in the cement, plaster, paint and other building materials.

This is why it’s a good idea to get into the habit of opening the windows, using a dehumidifier, and keeping the property warm and aired out for a while after you move in – especially since your day to day living activities will be adding even more moisture from cooking, showering, and even keeping household plants.

If you ventilate the property well, moisture will eventually decline to more normal levels.

How to Stop Condensation from Forming

There are many causes of condensation in the home, but by far the most common cause of condensation is poor ventilation. This means that to reduce or get rid of condensation you need to reduce moisture levels in your home. Typically, energy saving advice involves stopping as many draughts as possible, but you can go too far with sealing your home. If you have done any of the following:

  • Plugged up ventilation panels

  • Closed the window trickle vents

  • Started drying your washing on your radiators instead of in a tumble dryer

  • Told people to keep the windows closed when cooking/showering

Then you could be creating a condensation issue in your home.

Condensation is more likely to happen in a room that is very humid. The average home is somewhere between 40 to 60 percent relative humidity, but we don’t notice that because the water is just moisture in the air – indeed breathing slightly humid air is usually nicer than breathing completely dry air. When that moist air hits a cold window, though, it turns to condensation and starts running down the window, pooling at the bottom and potentially causing mould and mildew build up. In fact, condensation is the leading cause of damp, and mould on walls.

How to Reduce Condensation on Your Doors & Windows 

The best solution to condensation and high humidity is good ventilation. Here are some tips on how to reduce condensation in your home and prevent condensation build up on patio doors, windows and more:

  • Opening trickle vents – the small vents fitted above your window glazing – across your home can do a lot to help stop condensation build up.
  • If you have a condensation problem in your bathroom, get into the habit of opening the windows after you shower.
  • To stop condensation in the kitchen, fit an extractor hood or fan over the cooker so that it can vent moisture to the outside. You should also open the windows as much as possible.
  • If you have them, open the trickle vents in your bedroom. If you don’t like sleeping in a cool room, leave the windows closed overnight, but open them slightly when you get up in the morning. Two sleeping adults can produce as much as a pint of moisture between them per day, which is why you’ll often find condensation on bedroom windows in the morning.
  • If you can’t ventilate the house properly, consider getting a dehumidifier. These are quite inexpensive to run and will go a good job of getting rid of excess moisture. Dehumidifiers are particularly useful in parts of your home with minimal air flow.
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