Rule 8: ventilation

The silver bullet for almost all damp, rot or mould is ventilation.

Every London property suffers from excess humidity to some degree, especially ground floor bedrooms, as occupiers are reluctant to leave windows open, especially when away.

1. Install an external vent to the bathroom, either a humidistat (humidity activated vent) or one that is switched on when the lights are turned on and remain on for at least 20 minutes.
2. Install an external vent in the kitchen that occupiers are encourage to use.
3. Keep a window permanently open, or ajar in the property. It is often a good policy to keep a top floor window, sky-light or Velux permanently open.
4. Make sure rooms are easy to ventilate. Occupiers are not always good at keeping windows open, especially during cold winter nights.
5. Vent chimney breasts, chimneys should be capped with a vent or cowl (if not used for burning fuel). Chimney breasts are the ideal form of ventilation as;
   1. They are passive i.e. not driven by electrics or other means that can be switched off,
   2. Quiet, so not encourage occupiers to close them,
   3. They naturally draw air continuously out of the room,
6. Don’t dry clothes indoors without an externally vented drying machine. If this is too restrictive, then select one well ventilated room, with the door closed, such as a bathroom.

Heat and insulation

1. Maintaining a minimum temperature of 10-12˚C, especially at night. The cost of steady heat is less than fluctuating heat, given the reduced insulation caused by condensation.
2. It is recommended to use a modern thermostat (Nest, Hive etc) that allows many different minimum temperature settings. This method allows you to keep multiple settings including a minimum night time temperature, throughout the year, with a small amount of heat circulating through the property when the walls are cold.
3. Consider thermal insulating plaster board for shaded or north facing walls.

Sub-floor and loft ventilation

1. Make sure you have a flow through of air from front to back of a property.
2. Consider vulnerable areas such as obstacle, especially if the height of the void is low.
3. Consider if warm humid air can enter the sub-floor void. One of the greatest property crimes, is extending the rear, but allowing warm humid air, perhaps from the kitchen to be drawn via the vent into the cold sub-floor void where it condense.
4. Telescopic or periscopic vents reduce airflow – consider whether there is sufficient alternative airflow.
5. Consider leave a wifi or bluetooth connected hygrometer or data logger in the sub-floor void and a hole to regularly observe the sub-floor state using a borescope.

Ventilation is the key to virtually all damp, codnensation, “rising damp” and even penetrating damp to some degree.