What is the Cause of Damp in Bathrooms

By Ruth MacEachern

Product Manager

During the winter months, colder weather may mean that you may start to see mould growing on your bathroom walls and ceilings – particularly if you live in an older house with poor insulation. Dark patches of mould growing in your otherwise clean bathroom can be unsettling, and pose a risk to your health, but they are also a signal that your property may have an underlying damp problem that could cause damage to the fabric of the building and result in expensive repairs if it is not dealt with.

While there are various causes of damp in UK homes, a damp patch in your bathroom is most likely to be a result of either penetrating damp or condensation damp.

Penetrating damp in bathrooms

Penetrating damp is caused when water is getting through the envelope of your home or leaking internally. In most cases, penetrating damp soaking through from behind will leave a brown stain on the surface of the wall which is caused by the pigment of the plaster or rusting metalwork inside the wall.

Penetrating damp in your bathroom may be caused by water leaking from pipework, in which case you will need to contact a plumber for repairs or could be entering through a gap around a window or a hole in your ceiling, in which case you should contact a builder.

Condensation damp in bathrooms

Condensation damp forms when water vapour released from the air as it cools soaks through a porous surface such as paintwork. Condensation damp is quite common in bathrooms, as their use creates a large amount of steam. Taking a bath or shower can result in more than 600ml of liquid water escaping as steam, which will form droplets of condensation when it settles onto a cold surface.

Condensation damp can be tricky to deal with in a bathroom and the only real solution is to improve the airflow so that moisture laden air can be removed.

Opening a window when you take a bath or shower can help to reduce humidity, but in some cases, it can cause the humid air to spread around the rest of your home, creating damp patches and mould in other rooms where it becomes more of a problem. Instead, you should use a bathroom extractor fan.

Extractor fans such as the EnviroVent Cyclone 8 work by sucking the humid air out of the bathroom and expelling it to the exterior of your home where it can dissipate. This creates slight negative air pressure in the bathroom which prevents the steam from spreading around your home.

In most houses, the extractor fan should be connected to the same circuit as the lighting in the bathroom so that it runs automatically, and ideally, you should run it for 30 minutes after bathing to ensure that all the humidity is removed. Optionally, modern extractor fans may feature a humidity sensor. This measures the amount of water vapour in the air and adjusts the power of the fan to remove the moisture-laden air more quickly and then switch off when condensation is no longer likely to form.

Find out more

Are you concerned about a damp or mould patch in your bathroom? Book a free home survey from one of our local ventilation consultants. They can visit your home to identify the cause of the problem and provide you with advice about the best solution for your needs. Enter your postcode below to get started.