How do I ventilate my home properly?

Modern homes are sealed against draughts, which saves heat and traps moisture. The result is condensation and mould in houses that were previously fine. Deliberate ventilation replaces the uncontrolled ventilation that draught-proofing removed.

What you'll need

• Windows that open (optional)
• Working extractor fans (optional)
• Hygrometer (optional)

Step by step

1. Ventilate briefly and fully rather than constantly and slightly.Windows fully open for five to ten minutes exchanges the air with little heat loss. A window ajar all day cools the walls and furniture, which costs far more.
2. Use extractor fans during and after moisture-producing activities.Showering, cooking, drying clothes. Run the fan for fifteen minutes afterwards, which is when most of the moisture is still airborne.
3. Open trickle vents and leave them open.The small vents in window frames. They are there deliberately and closing them is a common cause of condensation problems.
4. Do not block air bricks.They ventilate underfloor voids and, in some cases, are required for appliance combustion. Blocking them causes rot and can be dangerous.
5. Dry washing outside or in a ventilated room.A load of wet washing releases a great deal of moisture indoors. If it must be inside, use one room with the window open and the door closed.
6. Put lids on pans and use the extractor while cooking.Cooking is one of the largest moisture sources in a home and it is the easiest to control.
7. Leave gaps behind furniture on external walls.About 5cm. Air needs to circulate or the wall behind stays cold and damp, which is where mould appears first.
8. Measure the humidity if you have a persistent problem.A cheap hygrometer. Consistently above 60% indoors means the ventilation is insufficient for the moisture being produced.

Tips

• Cross-ventilation — opening windows on opposite sides of the house — exchanges air far faster than one window, so the period can be shorter.
• Bathroom and kitchen doors closed during and after use stops the moisture spreading into cooler rooms where it condenses.
• If a house is persistently damp despite good habits, a continuous mechanical ventilation system may be worth investigating.

Common mistakes

• Leaving a window slightly open all day in winter — It cools the walls, furniture and fabric of the room, which costs far more heat than a short vigorous airing.
• Closing trickle vents to stop draughts — They are the designed background ventilation. Closing them is a very common cause of condensation and mould appearing.
• Drying washing on radiators with the windows shut — It releases a large amount of moisture into a sealed room, which condenses on cold surfaces and causes mould.

Questions people ask