High Humidity Mould & Condensation

Condensation is the most common cause of mould within a property.

Unfortunately, student properties can be particularly prone to it due to the high levels of occupancy. Properties that have been recently modernised are also more susceptible to high humidity mould than older properties due to differences in ease of ventilation. This is made worse by tenants not heating the properties sufficiently in an attempt to save on heating bills.

The first sign of condensation mould is normally the mould growth on permeable surfaces such as walls and ceilings whereas impermeable surfaces such as windows and gloss painted surfaces will cause the water droplets to bead together. Condensation will occur on these permeable surfaces where extremes of temperatures occur.

High humidity mould is most common in bedrooms, bathrooms and in kitchen/dining rooms. The drying of clothes releases more moisture into the air which will exacerbate the problem. Having windows and interior doors closed prevents the air naturally circulating around the house.

High humidity mould caused by condensation is normally seasonally occurring during the colder months when windows may be shut and clothing dried inside the property, usually between October and April. During the summer months, the problem is usually not such an issue as windows are open more frequently and clothing is dried outside reducing the amount of moisture within the property. In addition, the outside temperature is closer to the inside temperature reducing the amount of condensation.

Due to poor ventilation, water vapour can build up within the property, from those living within the property through breathing, cooking, drying clothing inside without proper and effective ventilation.

High humidity mould can easily be prevented by those living in the property; experts are only a last resort should the problem be allowed to worsen.

1st Method – Improve Ventilation:

This is the simplest method of preventing mould growth. Opening a window slightly for an hour or so each morning and after showering will allow clean dry air to enter the house, circulate and replace the moisture rich air within the room. You must ensure that the windows, when left open, are not left unattended, or are open but securely locked in the ajar position. It is your responsibility that the security of the property is not compromised by windows being left open when ventilating the property. This should be done all year round. In bathrooms where extractor fans have been installed, ensure that they are working properly and not switched off.

2nd Method – Improve Heating:

To remove the moisture from the air, in addition to proper and effective ventilation, a slight gradual increase in low level background heating will allow the surfaces to warm slightly to reduce the risk of water vapour condensing on a cold surface. It will also warm the air temperature reducing the amount of water vapour in the air, therefore, removing the problem entirely.

To remove the black mould build-up, use an antibacterial spray and wipe any mould away every few weeks.

Further information can be found on the Sheffield City Council website: