Why do I get condensation and mould every winter?


First, we need to understand why condensation and mould appear every year when the temperature outside drops and the rain and frost make an appearance.

If you didn’t already know, condensation occurs when the moisture vapor held within the air (known as humidity) becomes too high. When combined with a drop in temperature, it reaches the dew point at which that moisture vapor forms into larger water droplets and finds its way onto cold surfaces.

Mould, on the other hand, forms on these cold, moist surfaces because these areas never fully dry out. Mould needs oxygen, food, and water to thrive, and with condensation occurring in your rooms, it creates a prime breeding ground for mould. Once mould has been established, the spores will keep spreading until treated.

The reason why condensation and mould are at their prime in winter months is primarily due to the fact that homeowners sporadically heat their homes to save on heating costs, and very rarely have any form of new air entering the property because it’s cold outside.


How to effectively stop condensation and mould:


Now that we know why condensation and mould appear, let’s look at how you can effectively prevent it from happening.

Generic advice on how to stop condensation and mould usually just says ‘stop drying clothes on radiators’ or ‘open windows’. While this information is fairly useful, it may not completely solve your condensation and mould problem.

In most cases, condensation and mould occur due to a lack of ventilation and poor heating during the day and night. Changing these two things will prevent it from happening.


Heating your home.


Let’s focus on how we can effectively heat your home to prevent temperature fluctuations that lead to condensation. It’s important to know that the higher the temperature, the more moisture vapor can be held within the air, but this is limited to the air space within a room if the doors are shut. If the temperature is low and humidity is high, the dew point at which condensation occurs is not far away (often just a couple of degrees).

If you have a thermostat, set it to around 18°C and leave it on. This will allow all surfaces and the air to be consistently heated to the same temperature and prevent the dew point from being reached. The boiler will simply kick in for a minute and then shut off, doing very little work to maintain the ambient temperature.

Worried about bills? Yes, it may cost a little more, but consider the times you turn your heating off. The temperature drops to a level similar to that outside, then you turn your boiler on for 4 hours in the evening, leaving it on until it reaches your desired temperature. After the 4 hours, you turn your heating off to go to bed and allow the temperature to drop. To where? The dew point temperature, causing all that vaporized moisture held within the air to condense.

Are you guilty of buying moisture traps or running a dehumidifier to control moisture? Well, you’re spending money on them, but they don’t exactly solve the issue 100%. So, heat your home and look to save money elsewhere if you can.


Ventilating your home.


Next comes the ventilation aspect, which is just as important to control condensation and mould in your rooms. The majority of mould problems occur in bedrooms, due to poor heating as explained above and a lack of ventilation during the day and night. Another contributing factor is that in bedrooms, we are breathing for over 8 hours, and if you breathe out through your mouth, that’s a lot of vaporized moisture being expelled into the air at 37.5°C and rapidly cooling to the ambient temperature. The size of the bedroom and the amount of furniture within it will also have an impact on how quickly the humidity levels will rise.

Now, this is where we need to explain the advice about opening windows a bit better. When you open your windows during the day in the winter months, you’re letting in new air, but it’s only drying the condensation that occurred the night before. The trick is to have a consistent supply day and night that’s large enough to prevent the humidity levels from getting too high, but not so much that you heat the neighbourhood and your boiler stays on constantly. This can be achieved by using the window night lock function or by installing a non-electric passive vent. We recommend the super acoustic controllable LookRyt vent by Rytons as it can be painted or wallpapered over to make it more discreet, and it also controls the noise from outside the property.


What forms of ventilation are available?


Window trickle vents are now compulsory in new windows and doors, but we would say that the amount of new air introduced inside isn’t quite enough to tackle a condensation and mould problem. If your windows don’t have them already, they can be installed into existing windows.

PIV (positive input ventilators) is a unit that introduces air from the outside into the property through a centrally located fan (usually in the hallway). The theory is that the new air is circulated around your property, reducing humidity levels and eliminating condensation. We are a little skeptical about how effective they are, especially if you don’t properly heat your home. If you like the sound of PIV systems, they do have some great reviews, but please do your research.

Dehumidifiers will remove moisture from the air, thus reducing humidity levels. But why don’t they stop condensation and mould? When condensation occurs, it’s not gradual, it happens pretty quickly when the dew point is reached and humidity is still high. The dehumidifier will only take in as much as it can handle at that time, and that’s why we don’t recommend it as a solution to resolving a condensation and mould problem. On the other hand, if you have to dry clothes inside and you’re trying to reduce the amount of moisture evaporated into the air, then dehumidifiers can be quite helpful. Take a look at dehumidifiers here.

Alternatively, place the clothes on a heated airer in the largest room and close to a window that is on night lock or has trickle vents or a passive vent.

Bathrooms are another troublesome area for condensation, and the same rule applies to extractor fans as it does for dehumidifiers. They can only handle so much at a time. So, when you have that hot, steamy shower with the window closed and think the extractor will solve your issues, you’re wrong. The humidity levels are like the Amazon jungle unless you have a very large bathroom, and the 15-minute hot shower generates steam that cools very quickly onto colder surfaces. Having the window on night latch all the time and opening the window when you have a shower will help prevent mould better than an extractor fan.

If you don’t have any windows in your bathroom, consider lowering the temperature of your showers by a few degrees and investing in a powerful humidity-controlled extractor fan.


Need more advice? Contact us today.

How to prevent condensation and mould in rooms.