Damp and Mould Growth

Description of Hazard

Dwellings should be free from rising and penetrating damp and free from persistent condensation dampness inherent to deficiencies or defects within building design and/or construction and be adequately damp proofed. Where defects are present they should be investigated and repairs carried out.

Properties should have adequate provision of natural and mechanical extract ventilation, i.e. a mechanical extractor fan provided to a bathroom.

Where a property has well insulated walls and roof, double glazing, adequate space heating, adequate damp proofing and a problem with black mould still exists, it might be the case that occupiers are inadvertently causing excessive moisture production and/or not ventilating the property adequately. This can be caused by certain household or lifestyle activities such as not opening windows during times of peak moisture production e.g. when cooking, bathing or drying clothes. Some households struggle to afford the costs of running their heating systems which does not help ease the problem.

Advice may have to be given to households on how damp conditions can be improved, or if significant damage is being caused to the property it may be necessary for a Landlord to discuss the terms of their tenancy agreement.

Types of Damp

Rising damp

Rising damp comes from the ground and usually only affects the ground floor and basements. It can cause skirting boards and timber floors to rot, plaster may bubble and solid floors may get fine white crystals forming. It is caused by moisture from the ground rising up through continuous fine pores in floors or walls. Its treatment can require extensive removal of plaster and injection of a chemical barrier. If only a small area is affected, this is unlikely to be a significant problem but if extensive or left to deteriorate, it can cause significant structural damage to the property and may also present a health risk. Rising damp is typically seen above skirting boards and appears like a wave or shadow of wet plaster.

Penetrating Damp

Penetrating damp often comes from leaking rainwater goods or overflow pipes and is resolved by addressing the structural defects which are causing water to enter the building. Often the dampness with dry out, however sometimes remedial plasterwork may be required. Penetrating damp often looks like isolated wet patches which could be located on walls or ceilings. It is usually confined to an area adjacent to the defective part of the building allowing water ingress.


Condensation occurs when air laden with water vapour is cooled by contact with a cold surface. It is most commonly seen on the surface of mirrors and toilet cisterns and around the edges of windows in cooler weather. Minor condensation is not a problem and occurs in most properties at some time but becomes serious when mould growth occurs extensively on cold surfaces and can affect clothing, soft furnishings and decorative finishes.

To keep your home free from serious condensation you will need to balance how you heat your property with the amount of ventilation that is provided. The recommended air change is 1.5 per hour. You will also need to minimise how much moisture is generated within the home. There may be obvious benefits to utilising a dehumidifier.

Damp in Old Buildings

Damp in old buildings with solid walls (including Granite construction) is often caused by the addition of modern materials to the older parts of the existing building. Modern plasters and finishes such as certain paints can stop the buildings need to “breathe”. Lime based mortars and plaster will allow the building to breathe as it was originally designed. Installing modern membranes and damp proofing can cause the building to lock in moisture and rot can set in within materials.

The ‘breathing’ analogy is a good way of understanding exchanges of air from solid masonry walls to atmosphere and back again. If air drawn into the wall is humid and the wall cools below dew point then water vapour in the humid air condenses as water droplets in the pores of the masonry. The stone may still appear dry. During warmer and drier times, some of this water will evaporate and leaves the wall as it expels the moisture. Even walls which seem dry will contain some water with the amount varying with changes in the season and climate.

It is important to correct any external deficiencies such as incorrect ground levels, broken gutters and flashings first. Then ensure the building has the ability to breathe. Never install modern insulations or membranes in older buildings without specialist consultancy first… the consequences can be more damp issues and additional costs.

Impact on Health

Exposure to damp and the associated mould can cause adverse health effects in susceptible persons likely to cause respiratory problems, respiratory infections, allergies or asthma. The vulnerable age group under the Housing Health and Safety Rating System is the under 14’s.

Damp and mould can sometimes affect the effectiveness of the immune system. The mental and social health effects of dampness and mould should not be underestimated. Damage to decoration from mould or damp staining and the smells associated with damp and mould can cause depression, anxiety, and feelings of shame and embarrassment. It is important to act against potential social isolation.


  • Property defects
  • Creating excess moisture from cooking, bathing and drying cloths
  • Poor heating
  • Lack of insulation
  • Poor ventilation


  • Good heating system and a good level of thermal insulation
  • Low-level background heating
  • Changing the surface finish of internal walls
  • Continuous low level background ventilation (don’t fully block chimneys)
  • Trickle vents into replacement windows, high level air bricks, or other passive ventilation
  • Mechanical ventilation or positive pressure ventilation system.
  • Dehumidifier use (Suitable for condensation problems only)

Useful Sources of Information


Damp and mould growth is considered to be a potential health and safety hazard in a dwelling under the Housing Act 2004.

Enforcement by the Council

You must write to your landlord in the first instance and request that they undertake any necessary repairs. If the Council has been notified that the landlord has failed to act and there is a legitimate issue in your property we will undertake an inspection and work with both the tenant and Landlord to resolve the issue:

The following is a very useful document with more information on Damp and Mould growth.