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Under the skin of the letting market

Here we share news and views on both the local letting market in & around Oxfordshire and all planned and recent legislation.


What causes condensation and mould in rental properties?


Stopping condensation and mould

In most cases condensation and mould build up is down to lifestyle rather than a problem with the property – always check if there has been a history of it before moving into a rental property.

Condensation occurs when water vapour in the air condenses into a liquid, for example, during the winter on to glass windows. It is a real issue between October and April as the external air temperature falls and water from the air forms as condensation on cold surfaces such as windows and external walls.

Everyone has heard the horror stories of bathrooms and kitchens with marked ceilings and window sills as condensation turns into black mould growth, but explaining to tenants that the cause is most probably due to their lifestyle – rather than underlying problems with the property – is not always an easy conversation.

The biggest hurdle is in explaining something invisible to someone. Water in the air from cooking, washing and showering is clearly visible as steam, but there is also much more water in the air that you cannot see, especially in areas where the water table is fairly close to the ground (as it is in Oxford) rather than buried many metres below it.

This ‘invisible’ water content is just waiting to condense on a cold window or north facing wall.

What causes condensation in homes?

1. Too much moisture in the property

Surprisingly 2 adults sleeping in an unventilated room for 8 hours release an average of 1.5 pints of moisture into the atmosphere.

Cooking – Cooking on the hob or boiling a kettle can produce up to 6 pints of moisture. Steam condenses on colder surfaces, exterior walls, tiles and windows.

Bathrooms and Laundry – This can produce up to 11 pints of moisture which may spread around the house and not just remain in the bathroom or utility room.

2. Not enough ventilation

Ventilation helps to remove moist air by replacing it with drier air from outside.
This normally fails when there is no extractor fan fitted in the bathroom / kitchen or when the fan has a separate switch which the tenant turns off.

3. Putting on the heating with no ventilation

Warm air holds more moisture than cooler air. Heating one room to a high level and leaving others cold makes condensation worse in the unheated rooms.

How do I stop mould and avoid being charged to remove it?

Generally, the tenant will be charged to get rid of mould if it arises from condensation which in turn is caused by tenant behaviour. Following all the instructions mentioned here should prevent mould occurring.

Mould can be wiped off with a proprietary fungicidal wash that is available from supermarkets. Make sure it carries a Health and Safety Executive (HSE) approval number and that you follow instructions for its safe use.

How to stop condensation and mould

1. Open windows and trickle vents! Even keeping a small window open will make a big difference.

2. Use and maintain extractor fans in kitchens and bathrooms and keep doors closed.

3. Dry washing outside where possible. Open a window if drying washing indoors or use a tumble dryer.

4. Ventilate cupboards and wardrobes – do not overfill. Let the air circulate freely.

5. Wipe water from windows and sills where condensation has gathered.

6. Draw back curtains in all rooms every day to avoid staining the linings.

This is one of the 50 most asked questions in our book: Landlord Intelligence.