Dealing with Condensation

Dealing with condensation.

At this time of the year we get a lot of calls about mould spots growing on walls, ceilings and even clothes and furnishings. Most calls are from tenants wanting to know what their landlords should be doing about the defective building unaware that the problem has more to do with lifestyle issues.

I know this is the boring bit but its important to know what condensation is and where it comes from.

There is always moisture in the air in the form of water vapour, although it can’t usually be seen. There is a limit to the amount of moisture the air can hold at any particular temperature, but the warmer the air is, the more it can hold.

So, when the moist, warm air comes into contact with a cold surface it can no longer hold so much moisture and condenses as water on the cold surface.

That’s where it comes from – so whats the cure?

There are two main things you need to do ( apart from ventilation which I’ll come to later).

Either the moisture content of the air must be reduced or the air needs to be warmer. In practice you will need to do both.

Now some interesting facts –

Every day the average UK household puts about 12 litres of moisture into the air in their home through normal activities such as cooking, washing clothes, and bathing: breathing alone contributes about 1 ltr per person every 24hrs. In homes where clothes are dried indoors or which use bottled gas heaters the total can be over 20 litres a day. Most of this moisture is produced slowly throughout the day in different rooms when it has a chance to disperse . The remainder is produced very quickly in the kitchen or bathroom where it is more likely to become a problem.

Typical moisture levels produced in a typical 3 bedroomed house per day –

A family asleep                          1.5 – 2.0  kg moisture.

A family during the day              2.5 – 3.5

Cooking                                    2.0 – 3.0

Washing and bathing                  1.0 – 1.5

Washing clothes                         0.4 - 0.6

Drying clothes indoors               3.0 – 5.0

Large dogs also produce high amounts of water vapour.

Things you can do.

Now that you know where the moisture comes from you can probably work out ways to reduce it, this might include – 

Keeping lids on saucepans, drying clothes outdoors, not using bottled gas fires and another useful tip when running a bath is to put some cold water in first, this reduces the amount of steam. Also closing doors to bathrooms and kitchens prevents moisture from seeking out cold surfaces in other rooms and producing condensation.

Ventilation

High moisture production is not necessarily a problem if there is enough ventilation particularly in kitchens and bathrooms where most moisture is produced.

I’m not sure how many people take a bath or shower in the winter with the window open but I wouldn’t think its very many so in most cases its best to install electric extractor fans which take the moisture laden air to the outside of the building. The best fans for the job are fitted with a humidistat control so they automatically respond to the amount of moisture in the air.

Heating

Condensation is almost bound to occur in rooms which are cold. The best remedy is to provide low background heat all day during cold weather. It is better to do this rather than relying on a high level of heating for short periods, and the cost is usually no higher. A minimum air temperature of 10 degrees C is recommended day and night.

I hope you have gained some useful knowledge by reading this but please remember this is a very simplified version of a very complicated subject and many technical books have been written on it. Most of the information I have given has been taken from the Building Research Establishment (BRE) Good Repair Guide series and other authoritive publications and, of course, my own experience.

Thanks for reading.

Tony Smith.  Certified Building Surveyor