To stop condensation on windows, reduce the moisture in the air and keep the glass warmer. Open trickle vents or a window for part of each day, run extractor fans when cooking and bathing, dry washing outdoors where you can and heat rooms steadily. Single glazing and failed sealed units run wettest, so replacing them helps.
Why condensation forms on windows
Warm air holds moisture. Cooking, showers, drying clothes and breathing all add water to the air indoors. When that air touches a surface colder than itself, it cools and leaves some of the water behind as droplets. Glass is usually the coldest surface in a room, so that is where you see it first, often on bedroom windows in the morning after a night with the door shut.
The GOV.UK guidance on damp and mould says an energy-efficient home is less likely to get condensation, provided it is adequately ventilated. A warm room with nowhere for moist air to go will still run wet, and so will a well-aired room with cold single glazing.
Where condensation appears and what it means
| What it usually means | What to do | |
|---|---|---|
| Inside face of single glazing | The glass is cold and heat is leaving through it | Ventilate daily and consider double glazing |
| Inside face of double glazing, in the morning | Moist air has built up overnight, often in a bedroom | Open trickle vents and heat the room steadily |
| Between the two panes | The seal on that sealed unit has failed | Replace the glazed unit; the frame may be sound |
| Black spots on frames, reveals or sills | Water has sat long enough for mould to grow | Clean the mould and deal with the moisture |
Everyday ways to reduce condensation
The GOV.UK guidance suggests two habits that cut moisture at the source:
- Cook with pan lids on, and keep internal doors shut while cooking and bathing so steam does not spread to colder rooms.
- Use extractor fans in kitchens and bathrooms. Humidity-controlled fans, or fans with an over-run that keeps them going after you switch off, work without anyone having to remember.
A few more habits help on top of those:
- Open trickle vents in rooms you are using, and leave bedroom vents open overnight.
- Dry washing outside when you can. Indoors, dry it in one room with the door shut and a window or vent open.
- Keep the heating at a steady, moderate level in cold weather, so rooms do not cool sharply overnight.
- Wipe the glass and sill dry in the morning so water does not sit on the timber or the seals.
- Leave a gap between large furniture and cold outside walls so air can move behind it.
Do trickle vents stop condensation?
Trickle vents are small, controllable vents in the window frame that let a steady flow of air in and out without opening the window. The GOV.UK guidance notes that under building regulations all replacement windows are required to have trickle vents, and that they should be controllable rather than permanently open. The Planning Portal explains that kitchens and bathrooms need higher rates of ventilation, while other rooms can rely on background ventilators such as trickle vents. The detail is in Approved Document F of the Building Regulations.
Tilt and turn windows give another option. The tilted position provides secure background ventilation, so a bedroom window can stay slightly open overnight. Our timber tilt and turn windows are available with trickle vents as well.
Condensation between double glazing panes
Misting or droplets between the two panes of a sealed unit mean moist air has got inside the unit, which usually means its seal has failed. Wiping cannot reach it and ventilation will not clear it. The glazed unit needs replacing. The timber frame around it may still be sound, so have the frame checked before deciding on a whole new window.
Will new windows stop condensation?
Better glazing helps with condensation on the inside of the glass. Modern double, triple, Slimlite or vacuum glazing keeps the inner pane warm, which is why upgrading single glazing usually ends the morning towel routine. GOV.UK also suggests considering replacing single glazing with double glazing. Timber helps here too, since the frame itself resists heat loss.
New windows cannot remove the moisture a household makes, so the habits above still count. A sealed-up house with closed vents and no extraction can still run wet, which is one reason replacement windows come with trickle vents. If you are weighing up glazing, our guide to double vs triple glazing compares warmth, weight and light, and our timber windows and heritage slimline windows pages list the options for each style.
What to do about mould around windows
If condensation sits on a sill or reveal for long enough, black mould can follow. GOV.UK advises that removing surface mould alone will not stop it coming back, and recommends mould and mildew products in preference to bleach. Larger areas need a professional. Deal with the moisture as well as the mould, and if you rent, tell your landlord.
Condensation and timber frames
Water that runs off the glass collects on the sill and the bottom rail of the sash or casement. On a timber window, a sound finish keeps it out of the wood. Wipe standing water away and touch up chips in the paint before winter; our timber window winter care guide covers the ten-minute yearly check. Water-sealed or pre-treated timber needs attention only every 5 to 10 years.
Do you need permission to replace windows?
For a house, new windows of a similar appearance usually do not need planning permission, according to the Planning Portal. Listed buildings, conservation areas and homes covered by an Article 4 Direction are the exceptions, and Greater Cambridge planning suggests its pre-application service for insulation and glazing work in listed buildings and conservation areas. Windows are controlled fittings under the Building Regulations. Schnauber is FENSA registered, so the work can be certified without a separate building control application.
Window advice around Cambridge
From our head office on Mill Road in Cambridge, we survey homes across the region, including Cambridge, Ely, Huntingdon, St Ives and Newmarket. If wet windows are one reason you are thinking about replacements, book a free survey and you will get a detailed, no-obligation quote for the windows you want to change.