Why are my windows wet every morning?

A sleeping adult adds a significant amount of water vapour to a closed room overnight. Meeting cold glass, that water condenses — which is why bedroom windows are wet in the morning and living room windows often are not.

What you'll need

• Window vacuum or absorbent cloth
• Hygrometer (optional)

Step by step

1. Recognise that some morning condensation is normal.It becomes a problem when it is persistent enough to keep frames and reveals wet, which leads to mould and, in timber, rot.
2. Leave the bedroom door ajar overnight.It lets moisture disperse through the house rather than concentrating in one cold room.
3. Open the trickle vent in the window frame.It is designed background ventilation. Many people close them without realising what they are for.
4. Wipe or vacuum the glass each morning.This is damage limitation rather than a fix, but wet timber and plaster is how condensation turns into rot and mould.
5. Keep a low background heat rather than letting the room go cold.Surfaces stay closer to the dew point. A cold room with warm moist air is exactly the condition that produces condensation.
6. Check whether the moisture is coming from elsewhere in the house.Laundry drying indoors, unvented cooking and long showers all raise humidity throughout.
7. Measure the humidity if it persists.Sustained readings above 60% relative humidity mean a genuine moisture problem worth addressing.
8. Distinguish condensation inside the glazing from condensation on the room side.Moisture between the panes means the glazing unit's seal has failed and the unit needs replacing. Nothing else will fix it.

Tips

• A window vacuum removes the water in seconds and is far quicker than a cloth if you have several windows.
• Condensation appearing on the outside of double glazing in the morning is a sign of good insulation, not a problem.
• If only one room is affected, look at what happens in that room rather than at the house generally.

Common mistakes

• Closing trickle vents to stop draughts — They are the designed ventilation path, and closing them is a common cause of new condensation problems.
• Ignoring it because it is only water — Sustained moisture on frames and reveals leads to mould and, in timber, to rot.
• Confusing condensation between panes with room-side condensation — The first means a failed glazing unit; the second is a ventilation issue. Completely different fixes.

Questions people ask