There are various forms of condensation and each form has it’s own unique set of causes and risks. Over the last 25 years our team at SPS Roofing Ltd have helped hundreds of customers fix roofing problems that have been directly caused by condensation build up, most noticeably interstitial condensation.

First of all let’s define exactly what general condensation is:

Condensation is the activity of water vapour held in the air being forced to condense from a gas to a liquid. It most commonly takes place when air with lots of warm moisture meets a cold surface, creating a reaction that forms either surface condensation or interstitial condensation.

However, in this article we are going to focus on helping you understand what interstitial condensation is, how to spot it, and potential methods of prevention.

What is interstitial condensation?

Interstitial condensation is a type of condensation which takes place between layers of a structure. Therefore it is of paramount importance to ensure that any roofing materials used are designed in a way of which prevents interstitial condensation by creating adequate amounts of ventilation that removes any condensation build up.

A build up of interstitial condensation can affect all areas of a property through the penetration of walls, floors, ceilings and most specifically for this article the roof structure.

This process sounds similar to that of surface condensation but the two do have their differences. Interstitial condensation penetrates the core structure of a building compared to surface condensation that is formed on the surface of a structure. Interstitial condensation is very hard to spot (due to it often being unseen) whereas surface condensation is typically visible.

What are the risks of interstitial condensation?

Interstitial condensation creates various ‘high priority’ risks that can be extremely damaging to your property. Left unchecked and free to build up overtime this form of condensation can be very costly to fix. In addition, interstitial condensation also contributes to an increasingly high rate of surface condensation build up on the exterior walls which creates further problems.

Here are some of the problems it causes:

• Rapid mould growth – it has been scientifically proven that people exposed to certain types of mould over a long period of time are more likely to suffer from respiratory allergies due to the harmful toxins produced. Conditions caused by certain types of mould include asthma, itchy eyes, respiratory infections, eczema and rhinitis. However, like with all types of mould and damp it can be incredibly hard to spot until it’s too late and significant damage has already taken place.
• Mildew – this a type of fungus that is distinguished by its cloudy, white appearance. You can normally tell the difference between mould and mildew because mould is typically a shade of black, blue, red or green.
• Staining – certain types of staining on your property could be a sign of a serious underlying issue. Types of staining to watch out for include wall tide marks and algae staining but all forms of unintentional stains should be inspected just to be on the safe side.
• Corrosion – this causes decay in a property’s structure and the materials used. In some cases it can even corrode the internal metal structure that supports a building.
• Frost damage & freezing – this takes place when water moisture formed by interstitial condensation freezes and then expands, which damages the masonry, and can be a leading contributing factor in the deterioration of a structure.
• Poor insulation performance & decreased thermal resistance
• Damage to electrical systems – this one does not need explaining. Water (moisture) and electrics have never been the best of friends.

The problems above are not intended to pressure you into taking a particular course of action. We feel that it’s necessary however to educate our customers on the risks involved in allowing interstitial condensation to build up without having an appropriate solution in place.

Before we move onto the solutions to fix and prevent the risks above from occurring, let us explain how to check if you have interstitial condensation in your property.

How can you check for signs of interstitial condensation?

You can check for signs of interstitial condensation yourself or hire a professional building inspector to undertake the ‘checkup’ for you. If the problems have occurred in your roof then you can always contact a qualified roofing company to arrange a free consultation and book in a roof inspection.

Here are some of the common signs:

• Check the paint work – in some cases it can cause paint to peel, harvest mould or damp spots, form bubbles due to the build up of water vapour, etc.
• Check the humidity – when humidity reaches high levels it will cause condensation to take place. Normally a room with a moderate to warm temperature will help reduce the rapid expansion of condensation but most cases a more serious set of actions must be followed to fully eradicate the issue.
• Seasonal vs constant – do you experience the problems listed in the last paragraph on a seasonal or constant basis?
• Increasing mould and fungal growth
• Cold or damp feeling on walls, floor or roof (especially if the current temperature has remained constant over a period of time)

Please note that as we described above, this form of condensation is in some cases very hard to spot. If you cannot find any of the common signs, then we still strongly recommend contacting a professional to undertake the inspection on your behalf.

How do you stop interstitial condensation?

Interstitial condensation can be a vey hard type of damp to fix due to the likelihood of not noticing it until the risks have been realised. This leads to very expensive repairs and in some cases a full roof refurbishment program having to be carried out. Therefore you should look to first take steps of prevention to stop it arising in the first place.

To stop interstitial condensation from taking place buildings must be designed in order to keep the temperature profile across the construction higher than that of the dew point temperature. The dew point is the temperature of which a gas is condensed into a liquid.

You can to some extent prevent interstitial condensation through monitoring and controlling interior moisture. The most common ways are through using dehumidifiers or ventilation fans/vents. Vapour barriers can also be used but you should always speak with a professional first before installing this type of prevention.

Another few methods to stop interstitial condensation is through vapour controlled layers positioned on the warm side of insulation, replacing old materials with newer materials designed specifically to resist condensation forming, ventilated cavities, and installing thermostat controlled heating to create a constant temperature.

Can these methods really fix the real problem?

We appreciate that these measures of prevention seem a little daunting and to be completely truthful with our customers, these prevention measures can often not solve the real cause of the problem. Unfortunately, it may be due to the roofing materials used and there’s no other option but to take drastic (and expensive) action to replace the roof itself.

If you are experiencing issues potentially related to interstitial condensation then please contact SPS Roofing Ltd or give our team a call directly on 01392 549740.

Just incase you would like to read a little more about this type of condensation, here is a great article we think has some useful information.