Damp and mould

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There are three main causes of damp and mould within properties.  

These are: 

  • penetrating damp 
  • rising damp 
  • condensation  

Penetrating damp

This occurs when there is a defect with the fabric of the building or services within it allowing water to enter the property.  For example a roof leak, disrepair to window and/or door frames or a leak from a water pipe within the property.

Penetrating damp can usually be identified by water staining, usually yellowy brown in colour, in a particular area where the water is entering the property.  The location of this staining is generally an indication of the source of the leak/water penetration.

Rising damp

Rising damp is caused by the breakdown, deterioration or bridging of the damp proof course of the building.  Moisture then rises up the walls to a maximum height of 1m.

As with penetrating damp it can be identified by a tide mark which can be yellowy brown or can be white and textured.  This texture is caused by salts from the ground and the plaster being drawn through the wall with water.


This is by far the most common cause of damp and mould within properties, particularly during the winter months.

As the weather gets colder and heating is turned on, windows are generally fully closed.  The average family produces around 20 pints of moisture a day and in an un-vented property, this moisture will condense within the property. 

This moisture can cause mould growth on walls and ceilings as well as on furniture and your possessions.

For more information on condensation and ways to control it please see our damp and mould leaflet.

The housing health and safety rating system (HHSRS) assessment 

When carrying out the HHSRS assessment the following items are taken into consideration:

  • energy efficiency, inadequate heating and insulation of the dwelling
  • background ventilation, lack of controllable background ventilation 
  • extract ventilation, lack of safe and accessible means for the extraction of moisture-laden air during cooking, bathing or showering 
  • clothes drying facilities, lack of facilities ventilated to the external air 
  • damp proofing, in disrepair or otherwise inadequate, resulting in rising or 
  • penetrating dampness 
  • disrepair, floors, walls or roofs allowing water penetration 
  • exposed water tanks and pipework, inadequate frost protection 
  • water using appliances, inadequately installed and sealed facilities, such as baths, showers, wash hand basins and wc basins which may permit splashing 
  • plumbing and waste pipes, inadequately installed, or disrepair to, waste pipes or plumbing serving water using appliances (such as baths, showers, wash hand basins, bidets and sinks) 
  • rain water goods, inadequate or defective 
  • roof and sub-floor spaces, inadequate ventilation 
  • small rooms sizes may result in high occupant density  

Just because one, or even several, of the above items is not satisfactory it does not mean the property would fail the HHSRS assessment.  For example, if the property has suitable background ventilation, mechanical extractor fans would not be necessary to control condensation caused mould growth.

Consideration is given to the age, design, location, condition and state of repair of the property as a whole.

Page last updated: 16 April 2020
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