How do I ventilate a bathroom with no window and no fan?

An internal bathroom with no window and no fan has no way for the moisture from a shower to leave. It spreads into the rest of the house, condenses on the coldest surfaces it finds, and the bathroom itself grows mould. It is a genuine building defect rather than an inconvenience.

What you'll need

• A squeegee
• A dehumidifier if the problem is severe
• A door that can be left open

Step by step

1. Accept what the physics allows.The moisture from one shower is a substantial amount of water. Without extraction it can only go into the fabric of the house or be carried out on air movement. There is no third option.
2. Reduce what you produce.Shorter, slightly cooler showers make a real difference. So does not running the bath while the room is already humid.
3. Squeegee the walls and screen immediately.Most of the water in an internal bathroom is on the surfaces, not in the air. Wiping it into the tray in thirty seconds removes far more moisture than an hour of airing.
4. Take wet towels out of the room.A wet towel evaporates its water into the room over hours. Hang it somewhere heated and ventilated instead.
5. Open the door straight after.Counterintuitive but correct where there is no extractor — the moisture has to go somewhere, and spreading it into a warm ventilated house is far better than leaving it condensing on cold bathroom surfaces.
6. Ventilate the room the moisture goes into.If the landing is where the humidity ends up, air that properly. Short sharp airing of the house does far more than a window on the latch.
7. Heat the bathroom.A warm room holds more moisture without condensing, and warm surfaces do not attract it. An unheated internal bathroom is the worst case.
8. Use a dehumidifier as an interim measure.A small dehumidifier run in the bathroom after showering will remove real quantities of water. It is a stopgap, not a solution, and it uses electricity to do a fan's job.
9. Get a fan fitted.An internal bathroom is required to have mechanical extraction. It is notifiable electrical work, so it needs an electrician, but the duct route and builder's work can be yours.
10. Deal with any mould already there.Clean it off, and expect it to return until the ventilation is fixed. Mould is the symptom, not the problem.

Tips

• Thirty seconds with a squeegee removes more water than any amount of leaving the door ajar.
• Leave the door open after showering in a bathroom with no fan, and closed in one with a fan. The right answer is opposite in the two cases.
• A dehumidifier in the bathroom after a shower is a stopgap worth using while you arrange a fan.

Common mistakes

• Keeping the door shut to contain the steam — With no extraction, containing the moisture means it condenses on the bathroom's own cold surfaces. That is exactly how internal bathrooms grow mould on the ceiling.
• Treating recurring mould with bleach and nothing else — Cleaning removes the growth and leaves the conditions untouched. It returns within weeks because the moisture is still there.

If it doesn't work

Questions people ask