After discussing the basics of condensation in the previous section, let's see now what are the main drivers behind it. Because condensation occurs as a result of an interaction between temperature and humidity, condensation can be driven by any of these two factors, namely:
This is the most obvious and most known form of condensation. It occurs when temperatures drop, typically during winter time, between October and April in the UK. So this is a seasonal problem that typically manifests during the winter months.
There is always a certain amount of humidity in the air. When temperatures are higher (e.g. in comfort range), the warm air "holds" the humidity in vapor form. Once temperatures starts dropping, the volume of the air and with this its moisture holding capacity decreases, discharging some of its vapor in form of condensation.
Where condensation occurs? On the coldest surfaces: typically bottom of walls, corners, cold window panes etc. The reason behind it: temperatures in a room are not uniform. Just because your thermometer shows 22°C for the room, it does not mean that you have the same temperature everywhere. Due to the cooling effect of the environment the external envelope of the building (walls, windows, roofs) can cool down significantly during wintertime. As a result, the temperature of the air also drops nearby cold surfaces, making these areas most liable to condensation. A temperature gradient can be observed nearby cold walls, temperatures dropping mm by mm in the immediate vicinity of a cold wall or a cold surface.
Condensation can occur both on the surface or under the surface, so we can have surface or interstitial (in between the pores or under-the-surface) condensation.Â
We can have condensation occurring even in well-heated environments if there is high enough humidity present. In old buildings this is rarely due to internal moisture sources (e.g. drying clothes indoors during wintertime), but the most common cause is an external (hidden) dampness source, often from some underlying condition. These can include:
In real life, the two sources of condensation often combine as both cold temperatures (cold walls) and excess humidity can be present. However, one of these factors often dominates and for the long-term resolution good diagnosis of the problem is vital.
The most common sign of condensation created by low temperatures (cold walls) is the presence of black mold. Mold appears on cold surfaces, typically in corners, around window frames or behind large pieces of furniture.
The most common factors that can contribute to the cooling of the building fabric and the appearance of condensation, are:Â
The root-cause of the problem here is the poor thermal insulation of (mostly) external walls.
Condensation can also be caused by the presence of high indoor humidity, which can be the sign of some other underlying problems. Condensation arising from high humidity or excess evaporation can be recognized from (some of) the following signs:
Heating and ventilation often won't solve these high humidity / evaporation related problems satisfactorily (although they can alleviate it) as it doesn't address the source of the problem. High humidity problems must be diagnosed, understood and if necessary, addressed as most of the time they are not "normal".
The diagnosis is not always easy as the source of the problem is often not obvious and/or requires specialist knowledge, measurements and a holistic understanding of buildings, materials and moisture movement. Do your best to debug it on your own using common sense, however don't hesitate to get professional help. A competent holistic dampness survey can save you time, frustration and money by helping you to get to the bottom of the problem quickly, avoiding (time consuming or sometimes costly) trial-and-error experimentation.
Here are some practical solutions related to this topic:
