Condensation and Dampness


It is again the season for condensation. All our Surveys provide advice on how to avoid condensation and some general advice is repeated below.

Condensation often appears in the corners of rooms, behind furniture, to the lower walls of bay windows and in loft spaces, beneath the under-felt. A modern vapour permeable underlay is no guarantee that condensation will not recur and the manufacturers of these products still recommend that some roof vents be installed.

Condensation can become a serious problem depending on levels of occupancy, ventilation and heating patterns. Condensation is normally most problematic in the winter.

Common causes of condensation are as follows:

  • Water vapour generated by normal activities such as cooking, bathing, breathing and clothes-drying will cause raised levels of humidity if there is a failure to ventilate the property adequately on a constant and daily basis.
  • Cool air holds less water vapour than warm air. Repeated cycles of warming and cooling will result in the condensation of water vapour on the colder wall and window surfaces.
  • Inadequate levels of heating combined with a lack of insulation within the fabric of the building. Condensation will be avoided if the fabric of the building is maintained at a reasonable and stable temperature. Heating should be constant but low-level avoiding significant fluctuations. This will be more easily achieved through the use of a central heating programmer and room thermostat.

Below are listed reasonable and practicable solutions which are both ‘building-related’ and ‘life-style related’. Addressing all together will significantly reduce the moisture, condensation and mould growth within the property. Mould growth which appears must be removed immediately with a proprietary cleaning product. Mould is harmful to health.


  • Install roof vents. An easy and cost effective way to do this is to install vented roof tiles. Typically three or four per roof slope at top and bottom. Where a loft is converted a system of eaves and ridge vents may be required with 50mm ventilation pathways between the rafters.
  • Consider insulating the walls internally. There is a range of natural or modern insulating products which could be used.
  • Use a natural wool insulation product in the loft. This will help moderate moisture content. Similar comments apply to lime plaster.
  • Install good quality mechanical ventilation in the kitchen and bathroom or shower room. Large capacity fans operating with a humidistat are better than those which operate only with a light.


Life-style Related Improvements

  • Ensure that windows are left open for a reasonable period each day, particularly during and after using the shower and after cooking. Try to promote a reasonable flow of air through the property by opening internal doors and both front and rear windows at the same time. It is arguably most important to maintain ventilation of this type in the winter months. If the fabric of the building is warm, and not just the air, then reasonable and controlled ventilation should not cause too much discomfort.
  • Condensation on the faces of windows will inevitably occur in winter. It should be wiped-off on a daily basis as and when necessary.
  • Clothes should be dried externally whenever possible. In winter it may be necessary to use a tumble dryer although these will still increase temperature and moisture content. Drying clothes internally and on radiators must be avoided.
  • It is important that the property is heated properly. Periods of relatively high temperature followed by lower temperature will exacerbate condensation problems significantly. A more constant lower level of heating is required. This will help warm the fabric of the building to help avoid condensation.
  • Minimise the number of house plants and pets present. All water used by plants will be directly transpired resulting in increased water vapour in the atmosphere.