Mould in my loft

What Causes Condensation In My Loft?

Why is the condensation occurring?

Condensation in your loft often occurs when the warm moist air from your home rises and comes in to contact with a cold surface (roofing felt), the air cools rapidly below its saturation point and the moisture within the air forms as droplets on you're roofing underlay. You notice these droplets more on surfaces that are not as absorbent as others. When this occurs it is known as surface condensation. This happens at certain times of the year as the roof surface temperature will be lower than the dew point, please see our commercial insulation pages as we explain more about it there.

condensation in your loft

How is the moisture produced in my house?

Moisture is produced all day and every day from your simple day to day activities. You cannot stop moisture production but you can help control it.

Typical examples of moisture production for a 3 bed detached home based on 4 people.

Sleeping : 1.5 litres of moisture
General activity : 3 litres of moisture
Cooking : 3 litres of moisture
Washing up : 1 litre of moisture
Clothes washing : 5 litres of moisture
Drying clothes : 5 litres of moisture
Bath / shower time : 0.6 litres of moisture

As you can see we can produce in excess 17 litres of moisture each day, If our windows are shut and we are not using any dehumidifying equipment this moisture needs to go somewhere. Moisture in its self is no problem but when moisture comes in to contact with a cold surface such as your felt its condensates and these water droplets can lead to an array of problems such as rot mould growth.

What is mould?

Mould's are fungi that require humidity, temperature and food requirements. Mould's grow at a rapid rate on material such as wood, plaster and bricks as these contain organic matter. Icynene is NO food source for mould. Hydrophilic moulds need high water levels, the fungal spores germinate when the conditions are right. Water damaged homes are common breeding ground for this type of mould. When surface condensation occurs the humidity will often be above 70% and the mould growth will establish.

mould in my loft

Why is the moisture passing through my traditional insulation?

People often get this mixed up and think that fibre insulation is an air barrier. Traditional insulation methods do NOT stop air leakage, Fiberglass and cellulose are often used in loft spaces but they will not stop warm air from passing from your home in to your roof space. This warm air passing in to your loft is not only one of the causes of your condensation but also the main causes of your high heating bill.

What are the solutions to your problem?


Is to add extra ventilation to your loft space, this will allow more air flow around your loft and take the moisture rich air out of the ventilation so the chances of condensation (the cause of mould) occurring will be reduced.

Why this method is not the preferred solution:

This method makes the loft space colder due to the extra air, this exchanges more air within your loft and in doing so cools your loft faster. As we mentioned earlier about traditional insulation methods not being air barriers this will simply take your warm air from your house quicker, cool your house faster and increase you're heating bills.

Not only will your heat loss increase but this will produce a stacking effect, stacking effect will be explained within our other blogs.

Please note : Cold roofs are more prone to condensation problems


Use the Icynene insulation installed between your roof rafters, This will covert your loft in to a warm loft instantly and help you get rid of your condensation issues whilst providing you with a healthier, quieter and more energy efficient home.


How Does Icynene work?

Most people know that mould occurs due to moisture but most home owners are unaware that 99% of moisture movement travels through the air. Its this airborne moisture leakage that can lead to mould, mildew and structural problems such a rot. As Icynene expands 100 times its original volume it is sure to fill all gaps, cracks and crevices. Traditional insulation cannot fill these gaps but Icynene can and will.

Icynene can deliver up to 50% more energy savings, lower fuel bills and reduce C02 emissions. As Icynene is made up of 98% air it allows your timbers to breath and should you get a roof leak the water will drain through the Icynene and not hold any water around the roof timbers so not causing rot. Icynene loses none of its insulation performance as it dries unlike other open cell foams.

To calculate what level of insulation you require your building will under go a U-Value calculation and a condensation risk analysis. These will enable us to provide you with the correct thickness of Icynene so you know your building is performing as it should and the chances of condensation occurring are removed.

To find out more information on the advantages of icynene please contact us on 07539 072 993

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