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Condensation as the name suggests is water which has ‘condensed’ from warm, moist air on contact with a cold surface. In recent years the incidence of condensation in buildings has risen from a level of comparative insignificance to become a major domestic problem. The increase can be attributed to changes in design of living accommodation and in the lifestyle of the occupants. A major factor in the last few years has been escalating fuel costs and a growing awareness of the need to conserve energy resulting in more widespread use of double glazing, better draught exclusion and in many cases increased us of paraffin and bottled gas heaters.


Condensation is chiefly a winter problem. The external air temperature is low and external walls and windows are cold.
The usual sequence of events is as follows:

1. Cold air enters the building
2. The air is warmed for the comfort of the occupants.
3. The warm air takes up moisture
4. The warm, moist air comes into contact with cold surfaces, walls, windows etc. and is cooled below its Dew Point
5. Condensation occurs as the excess moisture is released

Walls in kitchens and bathrooms (where moisture levels are usually highest), solid external walls, cold bridges such as concrete lintels set in cavity walls are commonly the areas in which condensation takes place. Intermittent heating and cooling of the property can aggravate condensation problems, since it allows external walls to remain cold and act as condensation points for damp air.


The main sources of moisture in domestic properties are :
     - Paraffin and unventilated gas heaters
     - Cooking
     - Clothes washing and drying
     - Baths, dish washing etc.
     - Occupants

Excluding heating it is estimated that a family of 4 with associated cooking, laundering, etc. will generate almost 14 litres of water a day. In addition, a free standing gas of paraffin heater could contribute a further 5 litres of water vapour. (4.5 litres of paraffin will generate 5 litres of water when it burns). This water, in the form of water vapour, must be absorbed by the air in the house or deposited out as condensation if corrective action is not taken


Running water on windows and walls is perhaps the most immediate indication of a condensation problem. If ignored, this can lead to a deterioration in the decorative condition of the property, stained curtains and decay in window frames.

The appearance of moulds on the surface of wallpapers and paints in poorly ventilated areas; e.g. behind large pieces of furniture, in cupboards and in corners of rooms is not uncommon and in severe cases may occur on furnishing, books, papers and even clothing in wardrobes.

Condensation can occur under suspended floors greatly increasing the chances of dry rot outbreak. A much less common form of condensation occurs when the Dew Point is reached, not on the surface of a wall but within the structure itself. This is known as interstitial condensation and can easily be mistaken for rising damp.


Condensation on walls will frequently start at lower levels where the air is coldest and spread out from corners where air flow is minimal. In such circumstances the dampness pattern can often be confused with rising damp. Careful observation and measurement will however, usually make distinction between the two very clear.

     Presence of running water on cold surfaces
     Presence of gas or paraffin heaters, wet washing, etc.
     Moulds, usually but not exclusively black on surface of paint or wallpaper, particularly in corners and behind large items of furniture
     Absence of hygroscopic salts

     Uniformly high moisture readings on wall surface (as distinct from a descending moisture gradient in the case of rising damp).
     Wall temperature below Dew Point
     High surface moisture level, lower subsurface moisture level (not always positive indication)


It has been shown that condensation results from moist air coming into contact with cold surfaces and that the likelihood of condensation increases with the amount of moisture in the air. Mould development within a building is unlikely to occur if the Relative Humidity is maintained below 60%

Installation of a “HomeVent” Positive Input Ventilation System in the attic space of a property will deliver fresh air to the central hallway, improve the air quality in the property and resolve condensation related problems.

Alternatively, in properties without a roof void, a “RoomVent” Positive Input Vent” can be installed in each of the effected rooms.

Home Vent
Room Vent