Condensation and Damp Problems

Condensation and Damp problems have causes that are not always easy to recognise. Read this simple explanation to help you decide whether a dehumidifier is really what you need.


Damp within the home has three main causes; rain water from outside, ground water from outside and condensation caused from inside.

Other possibilities include leaking pipes and construction Moisture (CM). CM is water trapped in building materials at the time of construction.

CM can be released into the home at a rate of around two gallons per day in the first year, and one gallon per day in the second year, after the building is finished.

CM is, therefore, a problem mainly for owners of new homes or substantial new home extensions.

If the problem is coming from outside, either rain or ground water, the solution lies outside too.

Check your roof, roof gutters and downspouts/downpipes for example. Damaged and decayed walls can also let in water, as can the poor state of mortar between bricks.

Pay attention also to surface drainage as this is often a source of problems with ground water.

In short, check that the outside of your home is protected from water before looking to the inside.

External maintenance problems can not be solved with a dehumidifier.

Once you have checked the outside, looked for the obvious water leaks on the inside (pipes etc.) and taken account of Construction Moisture if your home or extension is new, the most likely culprit is condensation, generated from inside the home.


Condensation is caused by moist air coming into contact with colder air or a colder surface.

All air contains moisture but when it is in the form of a vapor or gas we can't see it. When our breath looks like steam on a cold day what we see is a cloud of minute water droplets which have condensed in the cold air.

The most obvious sign of water condensing in our homes is on windows, mirrors and other smooth, hard surfaces. Where does it come from?

Unfortunately our day to day activities release a lot of water vapor. Breathing, obviously, but here are a few more examples:

  • Drying a typical load of laundry creates 10 pints.
  • Washing that load releases another pint
  • Having that lovely soak in the bath spills out two pints
  • Cooking by gas adds another pint per hour.....and so on.

There are recommended steps you can take to reduce the amount of water that condenses, such as improving ventilation and background heating, and avoid allowing individual rooms to be cooler than the rest of the house.

You can also reduce the amount of water vapor produced by covering pans when cooking, venting laundry driers, avoiding drying of laundry inside the home etc.

This is all good, well intentioned advice but, not always practical.

Water condenses far more readily during colder seasons of the year. This is not always the easiest time to open lots of windows.

Wet, cold weather is not always the best for drying laundry outside and many of us live in apartments with few or no facilities for outdoor drying.

So, if you have a problem you have to weigh up the options.

Is running the heating longer, or on a higher setting, cheaper than buying and running a dehumidifier?

If I have to dry my laundry inside my home would a dehumidifier be better than dealing with the effects of damp?

We can't give you the answers but be as certain as possible that, for your situation, taking your priorities into account, a dehumidifier is right for you before you purchase one.

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