Condensation is a common problem, but there are a number of measures that can reduce or even eliminate its occurrence.

Introduction

Condensation arises as a result of warm, moist air coming into contact with a cold surface and when dew point is reached, the moist air will condense (e.g., dew on the grass on a frosty morning). Similarly within a building, if moist air comes into contact with a cold surface, this will give rise to condensation and resultant mould growth.
Theoretically, in a well-designed and well-constructed building, condensation should not occur. However, practically speaking it can be hard to avoid a certain amount of condensation arising in many buildings and unfortunately this is a fairly common occurrence, most noticeable from late October through to early March every year.
Condensation will give rise to water forming on cold surfaces. This will be particularly apparent on windows and to a lesser extent on other surfaces including ceilings, walls and floors. With excessive condensation levels you can in fact get streaming/pooling of water. With time, the water and condensation will give rise to mould growth on the various surfaces. Apart from its unsightly appearance, this can give rise to foul, musty odours. It can also give rise to damaged contents including clothes and in particular natural products such as leather and suede handbags and shoes. The mould can also be potentially hazardous to the health of the occupants, and in particular to babies/small children with underdeveloped respiratory systems. It can also have a significant impact on those suffering from asthma or cystic fibrosis. If the matter is allowed to deteriorate for prolonged periods it can in fact give rise to illness and harmful side effects to all occupants. Clearly, condensation and mould growth are an undesirable burden and an attempt should be made to eliminate or at least reduce this as far as is practical.
In practice, the level of condensation is largely affected by the particular environmental conditions. A number of factors affect the levels of condensation, including relative humidity, ventilation, heating and insulation.

With excessive condensation levels you can in fact get streaming/pooling of water. With time, the water and condensation will give rise to mould growth on the various surfaces. Apart from its unsightly  appearance, this can give rise to foul, musty odours.

Relative humidity

The relative humidity is in effect the amount of moisture vapour in the air at a given time. Everyday activities including breathing, cooking, washing, etc., will all give rise to moisture vapour being discharged into the environment. Activities such as showering and drying clothes will give rise to particularly excessive amounts of moisture vapour and hence a high relative humidity.
Whereas it would not be practical to prevent or avoid the creation of moisture vapour within an environment, the aim should be to reduce this, where practical, to an acceptable standard. In this respect, certain activities such as drying clothes within the house on radiators or clotheshorses should be avoided. In the event that high moisture-producing activities are to proceed, then we strongly recommend that a dehumidifier be obtained and used regularly with a view to extracting the moisture from the air.

Ventilation

It is important to ensure good levels of ventilation in order to minimise the risk of condensation occurring within a property. The most effective form of ventilation is natural ventilation, i.e., opening windows. Provided that windows are opened regularly, it should be possible to control or eliminate any significant levels of condensation. It is, however, our experience that many occupants, and particularly tenants, seldom open windows, and thus the risk of condensation occurring will be higher than normal. It is also a requirement that provision be made for permanent vents to habitable rooms (living rooms and bedrooms), in order to ensure a constant trickle of background ventilation and therefore minimise the risk of condensation occurring. Permanent ventilation is often provided in the form of slot vents within window frames or via ventilation grilles in external walls. It is important to ensure that these are kept open/clear for maximum efficiency. It is also a requirement to have mechanical extractor fans within bathrooms and over the cooker in kitchens in order to extract as much vapour as possible at the source. It is important to ensure that these are used during and following showering and cooking. It is also prudent to have the fans cleaned/serviced regularly in order to ensure that they are operating at maximum efficiency.

Heating

The levels of heating within an environment will affect the amount of condensation. Basically, the higher the level of heating, the lower the risk of condensation occurring.
This is because warm air will hold more moisture than cold air. We would also caution that it is our experience that many occupants, and particularly tenants, often cut back on the heating in order to minimise running costs. Again it is important to ensure that the heating is used regularly during the colder periods.

Insulation

Again the levels of insulation will affect the potential for condensation to occur within a property. Basically, the better the insulation standard, the lower the risk of condensation occurring. This can be particularly evident in areas of ‘cold bridging’ between the interior and the exterior, such as window reveals, where insulation may have been omitted at the time of construction.
More modern buildings tend to be reasonably well insulated; however, older buildings are likely to be poorly insulated. All surfaces need to be considered in order of importance as follows: windows, as they tend to have the coldest surfaces; ceilings, as the heat (and warm moist air) tends to rise; walls; and, lastly, floors.

Clearly, condensation and mould growth are an undesirable burden and an attempt
should be made to eliminate or at least reduce this as far as is practical.

Remedial works

In order to eliminate/reduce condensation, these factors need to be addressed. The first three factors can be addressed relatively easily by changing user habits with minimal capital expenditure. The fourth item, which involves upgrading the thermal insulation standard, is more disruptive and would involve capital expenditure. In this respect, we would recommend the following practical steps.

Reduce moisture levels:

  • be mindful of moisture-producing activities and reduce where possible, e.g., shorter duration for showering;
  • try and avoid or at least minimise drying clothes on radiators/clothes horses;
  • close doors to bathrooms after showering; and,
  • if it is inevitable that excess moisture is going to be created, then obtain and utilise localised dehumidifiers.

Increase ventilation levels:

  • open windows regularly to ensure regular air changes, particularly after showering;
  • ensure that all habitable rooms have functioning permanent vents – ensure that these are well positioned within the room and are clear/unobstructed; and,
  • ensure that mechanical extractor fans are fitted to kitchens and bathrooms – vents should be located close to or directly over the source of moisture, and should be fitted with time delay switches so that they stay on for a minimum four to five minutes after switching off. Look at modern/whole ventilation solutions such as heat
    recover/humidity stat controlled vents.

Increase levels of heating:

  • ensure that the heating is used regularly during the colder months; and,
  • consider providing additional localised heating to supplement the existing heating installation during the colder months.

Upgrade insulation standards:

  • look at quality/standard of windows and upgrade/replace;
  • review and upgrade insulation standard to the ceilings/roof;
  • review and upgrade the insulation standard to the walls; and,
  • review and upgrade the insulation standard to the floor.

When the principles are fully understood, by tweaking and working on the above factors, it should be possible to eliminate or at least reduce the levels of condensation occurring within a dwelling to an acceptable level.

Val O’Brien BSc (Hons) MSCSI MRICS Dip Proj Man

Chartered Building Surveyor