Preventing damp and mould

Many people have experienced issues with damp and mould in their property at some point.  Even in warm, well looked after properties mould growth can occur in some parts of the home, especially in the colder months.  Most mould growth people will experience is most likely to be the result of condensation, however some instances of damp and mould may be the result of damp.

Below you can find some information about damp and mould in the property looking at the main sources and some helpful tips for how to minimise damp, condensation and mould in your home.

Causes of dampness and condensation in your house

  • Lack of adequate heating and/or ventilation.
  • Water coming in from the outside through leakage, seepage
  • Rising damp - dampness from the ground rising up into the building fabric
  • High levels of moisture/water vapour being produced inside the house

Why it is important to keep a house dry as well as warm

Moulds and other fungi can grow in damp homes, particularly in areas where there is restricted ventilation, such as inside cupboards and wardrobes.


Air contains moisture – this is called humidity. The higher the temperature of the air the more water it is able to hold. Air at 20°C can hold a lot more moisture than air at 10°C. The term ‘relative humidity’ describes how much moisture air contains at a given temperature. 100% relative humidity means the air is holding as much moisture as it can at that temperature.

The more humid the air is in your house, the more energy it takes to warm your house because it is also warming the water in the air. This means it will be more expensive to heat!

A good range of indoor humidity for comfort and health is between 30-60% during cooler months of the year. Mould is likely to occur if the relative humidity indoors is 70% or more for long periods of time. Keeping humidity levels under 50% also helps to minimise or control dust mites. But it is also possible to live in a house that is too dry! Humidity levels below about 30% lead to dry skin and nasal passages, increasing the potential for respiratory illnesses.

It is worth buying a low cost humidity meter from a hardware store and track how humid the air in your house is. You might be surprised at how quickly it can change, from morning to night, from room to room, and as the weather changes.

Humidity and condensation

When the humidity is high inside a house and it is cold outside the water vapour condenses on cold surfaces. The following areas might have problems with condensation and dampness:

  • Cold surfaces such as mirrors, windows, and metal window frames (‘crying’ windows)
  • Kitchens and bathrooms
  • Solid, uninsulated walls of unheated rooms
  • Cold corners in unheated rooms, particularly where outside walls meet
  • Wardrobes, cupboards.

Humid air and condensation can also be generated by things people do in their homes on a daily basis.

Sources of humidity and damp

Table showing sources of humidity and damp

Source of humidity/moisture

Litres of water vapour


Up to 3 litres per day

Clothes washing

0.5 litres per wash

Showers and baths

1.5 litres per person

Washing dishes

Up to 1 litres per day

Un-vented clothes drying

5.0 litres per load

Unflued gas heater

0.5-1.0 litre per hour of use

Breathing, active adult

0.2 litres an hour per person

Breathing, adult asleep

0.02 litres an hour per person

Pot plants

A high number of pot plants or if you frequently water them will increase humidity in your house

How to keep your house dry and avoid condensation

There are lots of things you can do to minimise dampness and condensation in your house.

Four key actions

  1. Reduce the amount of moisture produced in the home
  2. Provide ventilation, particularly in moisture-prone areas
  3. Increase heating to raise the temperature of the air and the cold surfaces
  4. Insulate the building to warm up cold surfaces and keep the heat in

Low cost options

  • On dry days open some windows to allow humid air to ventilate out of the house. It is better to open a few windows a little throughout the whole house. This helps the air to move through the house. One window open wide in one room may not be as effective. Try to do this as often as possible (2-3 times a week), but keep windows closed on wet days as damp air may increase indoor humidity.
  • Keep lids on your pots and pans when you cook – simmer rather than boil hard.
  • Keep the doors to the bathroom and kitchen closed when you are bathing or cooking.
  • Use thermal or lined curtains, keeping them open in the day and closed before dusk. This will capture the free heat from the sun and help to lift indoor temperatures.
  • Always wipe excess moisture from windows – if you don’t the moisture will collect on the frame which may start to rot. It may also re-evaporate during the day, raising humidity levels and making condensation worse when the room cools down.
  • Limit the number of pot plants in your house.
  • Install temporary plastic window insulation kits on your windows for the cooler months of the year.
  • Keep furniture away from outside walls to allow air circulation. Cool areas behind furniture will be high humidity areas conducive to mould growth.


  • On cold days try to keep indoor temperatures at least 18°C.
  • Try not to use a portable gas heater. They create high levels of humidity and are expensive to run. They also release harmful gases into the air.
  • Where possible install efficient heating, suitable for each of the rooms being heated
  • Install a heater in your bathroom.
  • Dehumidifiers extract moisture from the air and can help reduce humidity. However they do not tend to solve underlying problems of moisture getting into your house, excess moisture production in the home, and lack of ventilation and heating.

Drying clothes

  • Wherever possible, dry your clothes outside.
  • If you use a clothes dryer, make sure that it is vented outside.
  • If you must dry your clothes on a clothes rack inside, do this in a well-ventilated room with doors closed to the rest of the house.

More information

You can download an information sheet for preventing damp and mould in your property by following the link below. 

Preventing Damp and Mould Guide