Condensation forms when the air inside the house holds more moisture than it can keep once it touches something cold. On a winter night the coldest things in most rooms are the windows, so that is where the water appears. It is a ventilation issue rather than a window issue, which is why new windows still get condensation. The way to reduce it is to put less moisture into the air and to move the damp air out.
Where the Moisture Comes From
People are the main source. Breathing, cooking, showers, drying washing indoors and unflued gas heaters all put water into the air, and a closed-up house in winter has nowhere to send it. Bedrooms are usually the worst because two people breathe in a closed room for eight hours while the temperature outside drops.
That is why condensation says more about the house than about the window. Two homes with identical joinery can look completely different at seven in the morning.
What You Can Do This Week, for Nothing
- Air the house every morning. BRANZ tested this in a heated room and found that opening a window 300 mm reduced the moisture in the air by 14 per cent within 10 to 15 minutes. Its guidance on home ventilation also notes that a home with a condensation problem may need airing twice a day for two or three weeks before the moisture stored in linings and furnishings comes down to an acceptable level.
- Use the extractor fans, and leave the bathroom fan running for a while after a shower. Put lids on pots.
- Dry washing outside or in a vented dryer, not on a rack in the lounge.
- Heat the rooms you use. Warm air and warm surfaces hold off condensation; a cold bedroom with the door shut is where it is worst.
- Leave a gap behind curtains now and then. Heavy curtains keep the room warm but leave the glass colder, so the glass behind them is often wet.
Will New Windows Fix It?
No, and we would rather say so before you buy than after. New windows still get condensation. A window cannot remove moisture from the air, so if the house is damp the water has to settle somewhere. The home in the BRANZ guidance above that needed two or three weeks of airing was a modern one with double glazed windows.
There are good reasons to choose double glazing, Low E glass or a thermally broken frame, and those pages explain them. Curing condensation is not one we will promise. Ventilation is the answer, and it is the cheaper one, so start there.
Windows That Make Airing Easier
Where new joinery can help is in making ventilation part of the day. An awning window is hinged along the top edge, so rain runs off the outside of the sash and it can stay open in a shower. Fitted with a security stay it is restricted to a 100 mm opening, so a room can air with the house locked. If you are replacing windows anyway, tell us which rooms get wet and we will make sure each of them has a window you will actually open.
Mist Between the Panes Is a Different Problem
If an older double-glazed unit has gone misty between the panes, that is not condensation from the room. The seal around the unit has failed and the unit needs re-glazing, which in an aluminium frame is a straightforward job.
Rental Properties
If you rent out a property, the healthy homes standards set requirements for ventilation and draught stopping, which we touch on in our window replacement guide.
A Sensible Order to Tackle It
- Air the house, use the extractor fans and heat the rooms you use for three weeks, and see how much is left.
- Deal with the sources: washing dried indoors, an unflued gas heater, a bathroom or kitchen with no extraction.
- If the windows are hard to open, or you never open them because they are not secure, that is the point to talk to us about joinery that makes airing easy.
Contact Us
Tell us which rooms are wet in the morning and how you use them, and we will suggest where opening windows and stays should go. Call 09 278 4089 or use the form below for a free measure and quote.
