Condensation and Mould

Many people associate damp patches on walls or ceilings with defective guttering or issues such as rising damp. In fact, it is highly likely damp may be due to condensation which is common in all buildings. Unfortunately, many do not understand the issues of condensation, as although relatively easy to identify, is often difficult to remedy completely.

Condensation is a natural process, which unlike, Subsidence, Rising damp etc, is often caused by the occupants themselves. As such it can often be prevented, without too much alteration to the building.

Condensation tends to propagate at areas where there is a lower surface temperature, a term called thermal bridging, which generally tends to be e.g. breaks in Insulation, or inadequately sealed windows. 

Older, more traditional homes, particularly those from the Victorian era are probably more likely to suffer from Condensation problems, as these are not built to exacting standards in comparison to modern, cavity walled buildings, resulting in greater likelihood of draughts, (which in turn will increase your fuel bills) and differences in temperature.


Mould growth is not only aesthetically unpleasant, but it can be particularly problematic, specifically ‘Black Mould’, as the spores released can lead to respiratory problems, causing asthma suffers and those with weak or immature immune systems, breathing difficulties. As such, it is important, that condensation is dealt with, as if the source of moisture is not eliminated, Black Mould will continue to persist.


Causes of Condensation

Condensation is caused by a number of factors; however the main underlying principles which cause condensation issues, are insufficient ventilation, poor heating and high humidity levels.

  1. Moisture generation

Moisture may be produced from a number of different sources, and if this is not adequately removed, this can lead to problems. Moisture is particularly produced from tumble dryers that are not vented externally, drying clothes on radiators, showers and use of hot taps etc.

  1. Ventilation

Ventilation is essential to remove moist laden stagnant warm air from the building. To achieve this, there needs to be sufficient air changes of at least one per hour, in order to keep relative humidity levels below 70%. A compromise needs to be made, between providing sufficient ventilation to a building and preventing excessive heat loss.

  1. Insulation and heating

These two issues cannot be considered in isolation; as heating is required to ensure insulated external wall surfaces remain above the dew point (the temperature at which moisture in the air condenses). Intermittent heating can lead to condensation, resulting in cold external surfaces and high humidity levels. Problems may exist due to gaps in insulation, which leads to a process called ‘cold bridging’ occurring, resulting in moisture condensing at the un-insulated cold area.

See the article Common Causes of Condensation for more information

Identifying Condensation

Identifying Condensation and Mould is particularly frustrating, as it may not be taking place during the inspection, and/ or it may be concealed. A typical and common example of this is behind large cupboard units, which are built against an external wall.

However, principally, the main things to look out for are:

  • Water stains on surface of walls
  • ‘Mist’ on inside face of windows
  •  Damp patches with no definite edges
  • Black Mold growth (significant, as may rule out other sources)
  • Patches of damp behind furniture, or inside cupboards against external walls

In addition, humidity, presence of insulation, ventilation and heating patterns also need to be taken into account, which affects the potential for condensation occurring and black mold developing.

What you can do

As mentioned previously, there are many things that you can do that will often help, if not eliminate the problem of Condensation.

Following the simple steps, of reducing moisture produced, maximising ventilation and maintaining adequate heating as noted below may eradicate the cause of condensation.

  1. Reduce moisture produced: - Avoid excessive moisture being produced by altering living habits, such as avoiding drying clothes on radiators, open windows when cooking, using dishwasher instead of hand washing etc.
  1. Ventilation: - Tumble dryers should be adequately vented outside, extract fans providing minimum 15l/s within bathrooms, extract hoods to Kitchens. Other more costly options may be to install trickle vents to windows and or heat exchangers, to provide fresh air without loss of heat.
  1. Insulation and Heating: - Alter heating thermostat, to provide low level heating for longer periods, to prevent the possibility of intermittent condensation. Cold bridges can be avoided by ensuring cold patches are adequately insulated.

Once the source has been eliminated, you can look at removing the effects of condensation, which may involve stripping back wallpaper coverings, redecorations with damp and mould resistant paints.

If there is a large amount of moisture in the air, following a recent leaking drain which has since been repaired, or a plumbing fault, de humidifiers may be used (although generally only suitable as a temporary measure) to extract water vapour and reduce humidity levels.


Further advice

For further advice and or information, please contact us: Alternatively, you may wish to contact the companies in the resources section.