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A guide to condensation, damp and mould

Introduction to damp and mould growth

Here you will find information and advice to help landlords and tenants to identify and reduce condensation as well as treating the mould growth that often comes with it.

Damp can cause mould on walls and furniture and make window frames rot. Damp housing encourages the growth of mould and mites, as mites feed on mould and can increase the risk of respiratory illnesses in some people.

It is important to understand the different causes to allow effective treatment.

What are the three main causes of damp and mould?

1. Condensation

Cooking, washing, drying clothes indoors, even breathing can potentially cause condensation.

The first sign of a problem is water vapour condensing on windows and other cold surfaces, which then takes a long time to disappear, allowing surfaces to become damp. The second indication is black mould patches growing on these damp areas.

The 'amount' of condensation in a home depends upon three factors:

  1. how much water vapour is produced by the actions of its residents
  2. how cold or warm the property is
  3. how much air circulation (ventilation) there is

2. Damp - water leak

Damp can be caused by water coming through external walls or the roof. It can also happen when there is an internal leak or plumbing problem.

This can be caused by:

  • missing pointing
  • cracked rendering
  • missing roof tiles or defective rainwater goods
  • cracked water pipes, internal and external

Black mould is rarely seen on this type of dampness. This is because the affected area is usually too wet and the dampness contains salts or cleaning chemicals, will prevent mould growth.

3. Rising Damp

Caused by water rising from the due to a broken damp proof course (DPC) or passing through the natural brickwork if the property has no DPC. Usually only affects basements and ground floor rooms. It will normally rise no more than 12 to 24 inches above ground level and usually leaves a 'tide mark' low on the wall. If left untreated it may cause wall plaster to crumble and paper to lift.

Black mould will not usually be seen where there is rising damp. This is because rising dampness carries with it ground salts which prevent the growth of black mould.

Condensation and Mould Growth

Most homes will be affected by condensation at some point. It something that can be reduced or remedied without expensive works or treatments. Mould will thrive with four key elements:

  • moisture
  • food such as wallpaper or emulsion paint
  • right temperature
  • oxygen

By dealing with the causes of condensation you will automatically deal with the problem of mould.

Common Household Moisture Producing Activities

Everyday activities add extra moisture to the air inside our homes. The list below gives you some idea of how much extra water you could be adding to the air in your home in a day:

The list below gives you some idea of how much extra water you could be adding to the air in your home in a day.
Moisture sourceAmount of water added
2 people at home (16 hours)3 pints
Person sleeping½ pint
A bath of shower2 pints
Drying clothes indoors9 pints
Cooking and use of a kettle6 pints
Washing clothes2 pints
Bottled gas heater (8 hours use)4 pints

Five steps to reducing condensation and mould growth

1. Produce less moisture

Consider these ways to help reduce moisture within your home:

  • dry clothes outdoors if possible - avoid drying clothes indoors or if you have to, dry them on a clothes airer with suitable ventilation
  • vent tumble driers to the outside (never into the home) or buy a condensing type
  • cover pans when cooking
  • do not use paraffin or gas bottle heaters as they produce large amounts of water vapour

2. Remove Excess Moisture

Always wipe the windows and windowsills of your home every morning to remove condensation - just opening the window is not enough.

3. Heating

In cold weather the best way to keep rooms warm and avoid condensation is to keep low background heat on all day rather than short bursts of high heat. Good heating controls on your radiators, an independent room thermostat and a timer will help control the heating throughout your house and manage heating costs. Consider insulation (roof, cavity - wall or external wall insulation), draught-proofing windows and doors, and installing double or secondary glazing.

4. Ventilation

Finding a suitable balance between warmth and ventilation is important and can be very effective. By opening windows or ventilating your home it may appear that you are losing some heat, but what you are actually doing is allowing warm moisture-laden air to escape and replacing it with cool dry air from outside. Dry cool air is actually cheaper to heat than warm moist air! Many people who have double-glazing installed experience problems with condensation and mould growth that they did not experience with their old draughty window frames. However, by using trickle vents or opening windows slightly, then the necessary ventilation can be achieved.

5. Insulation

Insulating and draught-proofing will help keep your home warm.

  • insulate the loft to a depth of 300mm
  • consider secondary or double glazing
  • consider cavity wall insulation or internal dry lining
  • draught-proof windows and external doors - when draughtproofing, do not block permanent ventilators or rooms requiring ventilation

Dealing with mould

Mould can grow on walls, ceilings, furnishings and even on clothes and toys. Dealing with condensation and mould growth is not easy. Only carrying out one or two of the steps (below) may not solve your problem, you need to do as much as possible every day. Once a balance has been achieved your situation should improve over time.

  • carefully remove excess mould with a damp cloth and dispose - do not disturb mould by brushing or vacuum cleaning as this can increase the risk of respiratory problems
  • wipe down affected areas using a fungicidal wash or diluted bleach - remember always use rubber gloves and wear safety glasses
  • do not paint over any mould using an ordinary paint as it's likely to grow back, use a fungicidal paint instead
  • dry clean affected clothes and shampoo carpets where necessary

Advice for Tenants:

  • your landlord should not make unreasonable demands; for example, asking you to dry your clothes outside when you don't have access to outdoor space
  • contact your landlord or Letting Agent should the mould persist despite all efforts to prevent or treat it

Landlords should:

  • work with the tenants to determine the cause of the problem
  • carry out repairs to make good any defects identified at the property
  • after treatment arrange for redecorate using a specialist bathroom or kitchen paint, and if wallpapering the area make sure to use a good quality paste with an anti-fungicidal additive
  • where possible do not use wallpaper in bathrooms and kitchens and provide mechanical ventilation with a humidity sensor.

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