Surface Condensation

Surface condensation is by far the most frequently encountered form of dampness in buildings and generally it is the most easily recognised.

Factors required for Condensation

The factors required for surface condensation to form are well understood.  At any given temperature the air can hold a given amount of water vapour, the warmer the air the greater the amount of water vapour that can be held.  Should warm moisture laden air become cooled there reaches a temperature where the air can no longer hold the water vapour.  When this temperature is reached the air must release the water vapour; this is seen as Condensation and usually appears as droplets of water on surfaces.  However, the most telltale sign of condensation is the frequently associated development of mould growth.  The appearance of the mould may be black, white, yellow, green, etc., depending on the specific type of mould.

The temperature at which the air can no longer hold the excess water vapour is known as the Dew Point.  Surface condensation is thus formed when moisture laden air comes into contact with cold surfaces and the air in direct contact with the cold surface becomes cooled.  If cooled far enough it reaches the dew point temperature and the water vapour is released as condensation.

Moisture derived from baths, drying clothes, cooking, paraffin and flueless bottled gas heaters together with poor ventilation can aggravate or tip the conditions to cause condensation.

General Diagnosis of Condensation

Visual:   Where condensation is long term and severe this frequently leads to mould growth, water stains and severe decorative spoiling (mould growth is not common where the dampness is the result of active rising dampness).  It is mould growth that is the most commonly encountered sign that condensation/very high humidities exist.  Condensation can also be detected in very severe cases by the presence of water run marks or free surface moisture, ie a film of water or droplets of water on surfaces.  This never occurs as the result of rising dampness.

Occasionally diagnosis can be difficult since the problem may not be readily identifiable, eg low level moisture penetration or a defect in the floor/wall junction can appear similar to and confused with severe low level condensation.  In one case the dampness appeared to be due to an ineffective damp proof course but following investigation the cause of the dampness was shown to be condensation.

Instrumental Methods:   Positive diagnosis is best carried out using surface temperature thermometers and an instrument for determining relative  humidity, eg a whirling hygrometer.  There are electronic thermometers and hygrometers available but these can be expensive.  Where a mosture meter is likely to be used then some of the Protimeter (R) range of instruments include a thermometer head which is used to measure ambient and wall surface temperatures, as well as being able to determine  the relative humidity.  Once the air temperature, wall surface temperature and the relative humidity have been determined the dew point can be obtained from tables or a psychtometric chart.

Unfortunately, although there may be evidence of condensation, the conditions may not be suitable for it to be ocurring at the time of the investigation.  In such cases heavy reliance will have to be placed on the use of special items which can be left in situ to record the condensation if and when it occurs.  The best known are the Protimeter (R) 'Condensator', and 'Dew Tabs',  which undergo a colour change in the presence of active condensation.  In such  situations reliance will also have to be placed on the visible evidence, and possibly eliminating all other sources from the investigation.

Common Condensation Sites:  The following identify the most common areas of surface condensation encountered within the domestic environment.

Walls, floors and other flat surfaces:  Most problems are encountered in bathrooms, kitchens, bedrooms and where heating is intermittent.  A condensation problem is usually identified by the presence of surface mould growth (sometimes very severe), visible dampness on porous surfaces and sometimes water runs or collections of droplets on impervious surfaces.   (NB. rising dampness never forms free surface moisture.)

The results of severe condensation will usually lead to decorative spoiling; where conditions within the building are very severe then mould growth may also occur on furniture and backs of units, etc., well out of contact with the walls/floor.

One of the most commonly encountered areas for condensation to develop is in corners of external facing walls where mould growth can be seen to be rising from the floor in somewhat of a triangular pattern.  Wall/ceiling junctions and around window reveals are also common sites for condensation and the development of surface mould.

The result of severe and continued condensation on windows and other generally impervious surfaces where water can run and collect in contact with wood, might be fungal decay.  Similarly, condensate may also collect on window cills and soak into the plasterwork at the base of the reveal; this can  be confused with water penetration around the window frame.  On some aluminium framed units condensate will collect on the metal and run onto cills, floors, frequently causing severe wetting.  Again water originating from this source is often confused with other water ingress problems. 

Condensate may collect on unlagged cold water pipes and run off causing dampness and sometimes fungal decay should it wet wood for any length of time.

Dry lining techniques are sometimes used to isolate cold walls; if condensation occurs behind the lining problems can be encountered.  For example, if the board is porous (plasterboard) dampness may, for example, bridge across via plaster fixing dabs or any debris collected behind the board.  Where an air gap exists behind dry lining it must be ventilated.

Note:  Surface condensation is highly unlikely to occur on internal walls in the domestic environment since the required temperature differentials between rooms do not ususally occur.  However, if the adjacent room has been unheated for a long period of time and is open to the elements then it is remotely possible that condensation might occur on the dividing wall.

It is also unlikely that long term or severe condensation will occur during the summer months unless a considerable amount of water vapour is produced.  Short term, however, condensation may occur in bathrooms and kitchens where high levels of water vapour may be generated intermittently.

Sub floor area:  Problems can occur where water condenses onto the sub floor timbers and surface of the wall below a timber suspended floor.  Frequently, water droplets can be seen on the underside of floorboards and on joists; surfaces of the wall below floor level may also show the same symptoms.

Sub floor condensation is usually associated with the absence of suitable sub floor ventilation in conjunction with a damp sub site.  In this respect care must be taken when foam cavity insulation is installed since it is not uncommon for it to block the air vents.

Over a long period, sub floor condensation can lead to decay in flooring timbers which might eventually lead to structural collapse.

Roofs:  In pitched roof condensation is associated with roof insulation and lack of ventilation caused by blocking gaps between tiles and at eaves with sarking/roof insulation materials.  Water droplets can been seen on timbers and other surfaces during the more severe conditions, and care must be taken not to mis-identify the problem as a leaking roof.

Condensation in flat roofs frequently causes serious problems with the associated development of fungal decay; this can lead to structural collapse.  The problems can be caused by a number of factors depending on the particular design of the roof (cold/warm roof).  These include defective/absent or incorrectly installed vapour barriers, lack or absence of  insulation, and absence or inadequate ventilation (cold roof); it is not unknown for the problem to arise as a design fault.

Again, care must be taken to ensure that any moisture is not caused by a leak in the decking.

Chimney flues:  Condensation can develop in poorly ventilated chimney flues.  As a result damp patches can appear on the chimney breast and around the flue; generally it causes contaminant salts (hygroscopic)/extractives to diffuse through to the surface of the chimney breast which results in decorative spoiling, dampness and discolouration.