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What Causes Roof Condensation & How To Stop It

Roof condensation is a very common problem in the UK with around one in five properties being affected by it. Condensation on the bottom of the roofing felt is a typical problem in roofs of houses during the winter, when the temperature is low. If you are wondering what causes roof condensation, this article should hopefully address your concerns. 

This article is for you if you have experienced roof condensation and moisture in your roof. It shares information regarding what causes roof condensation and whether or not you need to consider re-roofing services to fix it.

Roof condensation

Below, you’ll find information on:

  • Factors that cause roof condensation.
  • Solutions to the problem that a professional roofer may put in place from outside the roof.
  • Ways to decrease condensation in the roof and other steps to decrease moisture.

Causes of Roof Condensation

To address the problem with roof condensation, we must first understand the reasons behind why this is happening. 

Condensation on the roof is an issue that many homeowners encounter. A poorly ventilated roof is frequently to blame for this issue. Mould can form on a roof that isn’t adequately ventilated, causing an increase in humidity. To make matters worse, mould can ruin the roof and cost you a lot of money in repairs.

Condensation on a roof can have a variety of reasons.


Constant humidity is one of the most prevalent causes of condensation. This problem can be solved by using a humidifier, but it must be utilised correctly. 

Lack of air circulation

To keep a building dry, it has to be well ventilated. In the absence of air circulation, moisture will accumulate on the roof. Because of this condensation, a dangerous accumulation of water vapour on the roof, compromising its structural integrity.

If your roof is more than a decade old, it may be time for a new one because of its age and degeneration. Before deciding whether you need a new roof, you should get it inspected by an expert.

When warm air comes into contact with a cold surface, such as a roof, it condenses into water droplets, causing it to rise. Inadequate insulation in the roof or the floor area above your home may contribute to this occurrence. Since your roof has an underside, heat from within your house may be escaping into this area and condensing as water droplets on its surface.

New windows and doors should be thoroughly sealed if they were recently installed, to keep the warm air from escaping. Checking for leaks around roof vents and chimneys, where hot air can rise through gaps and meet cool surfaces like ceilings or walls, will cause them to condense as an additional factor to consider.

Hot water tanks on the roof

If your property has a hot water tank in the roof, make sure there isn’t any steam escaping into the space below. A broken thermostat caused the water to boil continuously, resulting in condensation on the felt’s bottom. Even in the height of summer, this is a likely source of significant amounts of condensation.

Remember that not all roofs are affected the same by condensation and that this does not always indicate a problem with your roof system; it happens everywhere, sometimes!

Excessive moisture

As explained above, any moisture that comes in contact with a cold surface causes roof condensation even where there’s moisture in the home.

Most everyday tasks within a household can contribute towards producing excessive amounts of moisture. Some of them include showering and bathing with windows open, cooking or boiling water without extractor fans, drying clothes and using steam irons etc.

What Else Should You Look for on the roof?

Inspect any extractor fan ducting to ensure it is not dislodged or otherwise compromised. Leaks should be repaired if they are discovered. Look for any leaks in the roof’s plumbing pipes. Downlighters and plumbing that travel through the roof and into the rooms below can also allow moisture to get in, so these should be well sealed.

If they aren’t already, seal and insulate roof hatches. Because moisture condenses when it comes into touch with a cold surface, an increase in condensation in the roof may be expected if the humidity in the house is higher than usual.

Though the humidity and dew point in every home fluctuate, here are some typical household duties that might cause excessive moisture: Cleaning the bathroom, mopping, and scrubbing the kitchen floor.

Lack of ventilation in the house as a whole

Lack of ventilation in the home contributes to the formation of mould and mildew on the roof. Keeping their windows closed throughout the winter is a given for most people. Window trickle vents (or another form of window vent) should be installed and left open throughout the winter to ensure adequate ventilation. 

There should be no obstructions to wall vents or kitchen and bathroom extractor fans, and they should be utilised whenever practicable. Partially opening the windows in an empty room will enable fresh air to circulate. In addition to helping to keep the house warm, double glazing and wall insulation can also prevent moisture from escaping, increasing the amount of moisture that rises to the roof and condenses.

What Is “Excessive” Condensation in Relation to “Normal” Condensation?

Condensation is entirely natural on the roof during a cold spell. A lack of wind might exacerbate the situation by decreasing the amount of air flowing through the roof vents. When the temperature rises and the wind picks up, it should become apparent.

Warm temperatures or no clear weather would be a sign of excessive condensation. Excessive and troublesome condensation may have formed if the roof is wet, mouldy, and stale, with apparent symptoms of fungal growth on the timbers. 

Does Roof Condensation Occur In All Homes?

Some homes have roof condensation, while others don’t. This is due to various factors, including a home’s draftiness and insulation level.

Condensation is less common in a roof that has less heat loss. Old windows, uninsulated walls, and front doors allow moisture to escape, reducing the amount of condensation that collects on the roof.

Often, but not always, excessive roof condensation is caused by a mismatch between insulation and ventilation. It’s standard for homes built before the 1980s to have no, or very little, roof ventilation since they are so poorly insulated. Condensation in the roof may result if the insulation in these houses increase. Thus ventilation should also be built or upgraded at the same time.

Insulation installers seldom have sufficient knowledge or competence to determine the needed ventilation during the insulation upgrade, which is a huge problem. It is important to note that in certain homes, roof condensation cannot be totally eliminated. Still, the objective should be to decrease it to an acceptable level, such as when it develops gently, clears rapidly after cold weather, and does not contribute to mould or decay in the roof rafters.

How to prevent roof condensation

There are certain products that can be fitted into the roof to release moisture. But the steps below can be taken to reduce the amount of moisture being generated in the first place.

It’s important to trace where the moisture is coming from, where it’s going into and how you can prevent the same.

Some of the suggestions may seem obvious are worth exploring:

  • Keep the windows slightly open should you have the need to dry clothes on radiators during cold weather.
  • Keep the doors and windows closed when showering and bathing. Alternatively, you could use an extractor fan if you have one.
  • Keep the windows slightly open and use extractor fans when cooking and boiling water in the kitchen.

Still having trouble with roof condensation?

If you are still having trouble and not sure what causes roof condensation in your property, it’s always a good idea to get in touch with a roof specialist. At Premier Roofing Solutions, we have expert roofers who have worked on several projects that helped with this exact problem.

Contact us for a free quote and consultation to fix your roof condensation problems today!

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