Heat Loss From Buildings

Heat is lost from the interior of a building in two main ways: by transfer through the materials that make up the external envelope of the building (measured as a U-value) or by the exchange of air between the interior and the exterior environment that is, ventilation.

It is estimated that typical heat losses from a building are as follows:

  • Walls 35%
  • Roofs 25%
  • Floors 15%
  • Draughts 15%
  • Windows 10%


The rate at which heat is transferred through the external envelope of a building is expressed as a U-value. Heat always flows from a warm area to a cold area and each material component of the external envelope of a building transfers heat at different rates. The slower a material transfers heat, the better it is as an insulator. Low U-values are given to those materials that transfer heat slowly and are therefore good insulators; thus lower U-values are better.

For any given construction, independent of U-value, heat loss is also directly related to the temperature difference between the exterior and interior, and, to a lesser degree, the colour and texture of the external walls. Moisture reduces any material’s ability to insulate, as the conductivity of material increases when damp and with it the U-value; even moderate changes in dampness can significantly increase an element’s U-value, reducing its insulating properties. Common causes of moisture ingress include damp penetration in walls due to defective or removed render, leaking gutters and poorly fitting windows frames. It is therefore important to ensure that buildings are well maintained and weather-proofed to achieve low U-values.

Reducing Heat Loss in Buildings

Heat loss in buildings will always occur, but what the building occupier can do is try and manage how fast the heat is lost – this can be controlled through the use of appropriate construction materials and techniques in establishing and maintaining an airtight building envelope, incorporating high levels of insulation.

There are several ways to reduce heat loss in a building, these include but are not limited to:

  • Improving the insulation of the property (wall, roof, floors)
  • Reducing air leakage (windows, doors, extensions)
  • Reducing energy consumption by using efficient heating methods (replacing old inefficient boilers with more modern boilers or heat pumps).

The overall heat loss can be decreased by looking at all of the above and by adding insulation, or by ensuring that there are no gaps or excessive moisture in the existing insulation.

To learn more about how you can reduce your buildings heat loss please contact GES Energy today on www.gesenergy.ie


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