This occurs when warm air meets a cold surface: the moisture in the air cools and condenses on the surface in tiny droplets of water. Most commonly, condensation occurs on the inside of single glazed windows, but it can also occur on walls and within the fabric of buildings.
Condensation is a problem that has a number of causes:
- It can be an indication of the internal temperature being too low for the internal humidity level. This can happen in an unheated room that is not being used. The insulation of the whole building helps to solve this problem by evening out the temperatures internally, making it easier to keep the extremities of the house warm.
- It can also be an indication that humidity levels are too high and that water vapour produced elsewhere in the home is not being vented. The simplest way of avoiding this problem is to use mechanical extract fans connected to a humidistat, in both the bathroom and the kitchen. The humidistat will switch on when humidity levels exceed a predetermined limit. It is also a good idea to keep closed the door of a room where there is a source of water vapour.
- Condensation in an insulated house can also be an indication of cold bridging: where a non-insulated part of the construction protrudes’ through the well-insulated part and causes a surface in the interior to be at a much lower temperature than its surroundings. If the humidity level is high enough, condensation will form on this cold surface, possibly causing problems of deterioration. Cold bridging occurs most commonly at windows and where brick partition walls meet internally insulated external walls.
Cold bridging at windows
With double-glazed windows, the problem of cold bridging usually only arises with metal windows. Metal, being a very good conductor of heat (and thus a poor insulator), conducts heat much more quickly to the outside through the frames. If metal (either aluminium or steel) is to be chosen as a material for the frames then there needs to be what is called a thermal break incorporated into the frame. This is simply an insulating material sandwiched into the construction. Alternatively, wooden windows can be used— which is the more ecological solution anyway.
Cold bridging at partition wall junctions
This occurs with internally insulated external walls—any partition making a junction with the insulated wall bridges the insulation and loses heat much more rapidly at this point, producing a cold internal face adjacent to the insulated wall. This problem can be partly overcome by returning the insulation on the section of partition adjacent to the corner. If it is a plaster wall then the plaster can be removed at this point to be replaced by insulation.
To sum up: although ventilation and heating play a role in preventing condensation, good insulation correctly installed provides the most energy-efficient method of combating condensation.
