Cold attic spaces are at the greatest risk
84% of these attics are cold attics with natural ventilation.
There are many things that can cause problems with moisture and mould in the attic:
• Warm moist air from the indoor environment enters the cold attic through unsealed areas and condenses.
• Additional attic insulation means that the attic gets colder, which means that moisture condenses more easily.
• Changing a heat source also means changes to the air pressure throughout the house. Switching to ground source/district heating means that a chimney that was previously warm is now cold, and there is no longer any “chimney effect”.
• Built-in construction moisture can also cause moisture and mould in the attic.
• The ventilation requirement varies from attic to attic and during the course of the year. Ventilating an attic too much can also cause problems. If the outdoor air is cold, the air in the attic is cooled and can cause condensation against the cold outer roof. Or, when the temperature of the outer roof falls, for example after a warm day, the cooling and the increased relative humidity can lead to condensation on the inside of the roof.