New windows, and in the morning the glass is misted up? Usually that's not a fault in the windows, it's a sign your home now breathes differently.

It happens a lot: old windows are replaced, winter arrives, and in the morning the glass is wet and a dark patch appears in a corner. The first thought is that something's wrong with the windows. In most cases it's the other way round.

Why now?

Old windows leaked air everywhere. Uncomfortable and expensive, but moisture from the house escaped on its own. New windows seal very well, so moisture from cooking, showers, drying laundry and even breathing stays inside, and condenses on the coldest surface in the room.

On the coast this is even more noticeable. The air is humid most of the year, and in winter, when the southerly jugo wind blows, indoor humidity easily rises past the point where mould appears.

How to ventilate properly

  • Short and wide open. Several times a day, open windows fully for a couple of minutes, ideally two opposite ones to create a through-draught. The air is replaced before the walls have time to cool.
  • Don't leave a window tilted for hours in winter. The wall and reveal around the window cool down, heat is lost, and those cold surfaces are exactly where condensation collects.
  • Kitchen and bathroom right away. After cooking or showering, ventilate immediately and keep those doors closed until the moisture is out.
  • Don't dry laundry in a closed room. If you have to dry it indoors, ventilate that room more often.
  • Move furniture away from outside walls. A few centimetres is enough for air to circulate and keep mould from forming behind a wardrobe.

Condensation on the outside of the glass? A good sign

If you see dew on the outside of the glass in the morning, it means the glazing insulates very well, heat from the room doesn't reach the outer pane, so it cools like everything else outdoors. As soon as the sun warms it, the dew is gone.

When you should call us

If moisture keeps appearing in the same spot, where the wall meets the frame, under the drip sill or on the reveal, even though you ventilate regularly, there may be a thermal bridge or an installation problem. Then it's best for us to come and take a look.