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Condensation - How to Prevent & Control It

Updated: Jun 20


As we move through the winter months the enquiries that we get for damp issues increases. This is partly because the cold weather brings with it conditions that are conducive to condensation issues. In fact, the months of October to April are commonly known as ‘Condensation Season’ among surveyors.

condensation on surface

What is condensation and why does it cause so many issues? Quite simply, condensation is a process that allows water vapour within air to condense into a liquid on a cool surface. When this happens repeatedly over a period of time it can cause damage to finishes, mould growth, a musty damp smell and possible health issues.


Unlike other damp related issues, condensation has some distinct symptoms that can often be identified. Firstly, condensation enables mould to grow on the surfaces that it affects - in fact, it is the only damp issue that results in mould growth. That's not to say another damp related issue won't cause condensation, but it's worth bearing in mind.


Secondly, condensation often manifests itself as a crescent shaped stain (often with mould) in the corners of room, either high up at ceiling level, or low down near the floor. This is due to the lower level of air circulation in these confined areas.


What actually affects the likelihood of condensation forming varies and is dependent on several factors, including temperature and the amount of moisture in the air, or humidity. For condensation to form, the surface temperature must be below what is known as the ‘Dew Point Temperature’. We’ve all seen a condensation form on a chilled glass with your favourite cold drink, or on the inside of a glass window pane on a cold winters morning. In both cases, the temperature of the glass dips below the dew point temperature and condensation forms.


The trouble is condensation doesn’t just form on glass, it will form on any surface when the temperature is low enough and where the humidity is high enough. This often includes the internal faces of cold external walls.


The good news is we can control these contributing factors fairly easily;


  • Humidity - we all add moisture to the air every day, just each individual breathing can add about 100ml of water vapour to the air per hour. When we add in baths, showering & cooking, we can see how the amount of water released in to the air in our homes can be quite high. Simple measures such as using lids on pans when cooking and wiping down shower screens can help limit the amount of moisture we produce each day.


  • Ventilation – one of the biggest cures for condensation is ventilation. A warm, well ventilated home will be unlikely to experience condensation issues. The trouble is, when energy costs are high, opening the window after a shower, or keeping the trickle vent open on our windows can mean it will cost more to heat our home, right? Well maybe, but not always. During the cold seasons, increased humidity levels can lead to a stuffy damp environment, which can lead you to feel colder, thereby making you feel you need to turn the heating up higher. Conversely, a well ventilated, dry atmosphere can mean you feel warmer. So by providing some background ventilation in your home will reduce the risk of condensation and could mean you can turn the heating down a degree or two, potentially saving you money.


  • Heating – if condensation forms on cool surfaces, it makes sense that keeping your home warm will help avoid issues. One of the biggest causes of condensation, in our experience, is in homes where the heating is turned off while the occupants are at work all day. The typical schedule means that the property is cold all day and only warms up in the evening, when everybody returns home. They then do all the things that generates copious amounts of moisture (cooking, showers etc) and the moisture in the internal environment rises. The issue is that although the ‘air’ is warm when the heating comes on in the evening, the fabric of the building – mainly the dense external walls - never get a chance to warm up before the heating system turns off again. This means these surfaces remain cool enough to dip below the dew point temperature, often during the night. This stop/start heating schedule creates ideal conditions for condensation to form on these cool surfaces. Keeping the heating on a constant low temperature will help you keep your home warm and avoid this situation.


While controlling the humidity, ventilation & temperature will prevent condensation issues, finding the right solution has to be a combination of all of the above methods and this will be different for each home. It is also possible that a condensation issue can be the result of another damp problem, so if in doubt feel free to contact us about this or any other damp issue.


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