Why does my bathroom get so much condensation when other rooms do not?

Condensation is not a mysterious property of some rooms. It is simply water vapour meeting a surface below its dew point. Bathrooms produce more vapour than any other room and often have the least heating, which is the whole explanation.

What you'll need

• A working extractor, or an openable window
• A squeegee
• Optionally a cheap humidity meter

Step by step

1. Appreciate the scale of it.A ten-minute hot shower releases a substantial quantity of water into the air, into a room that might be eight cubic metres. That is why the bathroom, and not the kitchen, is where condensation shows first.
2. Find the coldest surfaces.Feel the walls, the ceiling, the window reveal and the mirror. Whatever is coldest is where condensation forms first, and it is usually an external wall or a poorly insulated ceiling.
3. Pull the extraction lever first.Removing the moisture while it is being produced is the highest-value change. Run the extractor from before the shower until well after — 15 to 20 minutes of run-on.
4. Keep the door shut while extracting.With a working fan, a closed door concentrates the moisture where the fan can reach it. Opening the door simply spreads it into cooler rooms.
5. Reduce the production.Shorter showers, slightly cooler water, and the lid down on the toilet. Small changes, but they compound.
6. Get the wet surfaces dry quickly.Squeegee the screen and tiles, and take wet towels out of the room. Standing water evaporates for hours after the shower ends and is a large part of the total.
7. Warm the room, at least a little.A bathroom kept a few degrees warmer has warmer surfaces, and warmer air holds more moisture before condensing. Heating a bathroom is not a waste.
8. Deal with cold spots specifically.A cold external wall corner, a single-glazed window, an uninsulated ceiling. These are where mould appears, and insulating or warming them is what stops it.
9. Stop drying washing in there.A load of wet washing releases litres of water over a day, into the one room least able to cope with it.
10. Measure if you are unsure.A cheap hygrometer showing relative humidity tells you whether your changes are working. Sustained readings above about 70 per cent explain recurring mould.

Tips

• Extraction beats everything else. If you only do one thing, run the fan from before the shower until 20 minutes after.
• Close the door if you have a fan; open it afterwards if you do not. The right answer depends on which you have.
• Mould grows where surfaces are coldest, which is why it appears in the same corner every year.

Common mistakes

• Turning the bathroom heating off to save money — Cold surfaces are half the equation. A cold bathroom condenses far more, and the resulting mould and decoration costs far exceed the heating saved.
• Treating recurring mould as a cleaning problem — Mould is the visible result of surfaces staying damp. Cleaning it removes the evidence for a few weeks and changes nothing about the cause.

If it doesn't work

Questions people ask