Condensation, mold and the role of External Wall Insulation
In a damp country like Ireland condensation is a common occurrence in poorly insulated house. Condensation can occur when warm moist air meets a cold surface at the dew point. This could be the surface of a wall, or even on a layer inside the wall (Interstitial Condensation). Condensation can damage the fabric of a wall and lead to more frequent redecorating. More seriously, condensation leading to the growth of mould and mildew can cause ill heath for the occupants. Everywhere that liquid water and heat are found in a home you will always find a fungal growth.
Fungus and mildew are seen as triggers for asthma. Ireland already has the fourth highest incidence of asthma in the world and allergies are rising fast. Alarmingly things may be getting worse: recently the World Health Organisation has found that as many as third of Irish children now have asthma.
Condensation is the formation of liquid water from air when the temperature of the air reaches its dew point. This is most lightly to occur during winter months when the walls are cold and the internal air is warm especially in locations where the relative humidity of the internal air is high Bathrooms and kitchens are common locations where this occurs, but also bedrooms in the early hours of the morning.
How condensation manifests depends on the type of wall insulation in the house. With non insulated walls condensation normally occurs on the inside surface as the wall is cold. For houses with internal insulation the risk is that condensation will build up behind the insulation where moist air comes into contact with the cold external wall. (Click here for a very clear account of what can go wrong) In the case of poorly constructed cavity insulation walls, interstitial condensation can occur. So the fabric of the house will suffer from cracks as the water inside the wall freezes and thaws. As SEI say
"The danger of interstitial condensation is that it is, by definition, hidden within the structure and therefore may be reducing the thermal performance of the envelope unknown to the homeowners, potentially causing structural defects in the medium to long term as well as health risks from resulting mould growth."
Source Page 24 http://www.sei.ie/retrophguidelines
Using good quality external insulation ensures that the entire fabric of the house remains warm and so the dew point is brought outside the building. This means that condensation can not occur inside the building. The biggest risk is if the insulation is not correctly bonded to the wall, moisture can build up behind that layer.
To ensure that the insulation is fully bonded to the wall, you need to ensure that approved (ETAG 004 or better) external wall insulation systems is used on your home.
In Ireland NSAI (the national standards authority of Ireland) approve External Insulation systems as a part of their ETICS Scheme.