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Cyngor Sir Ynys Môn - Isle of Anglesey County Council

Damp, condensation and mould

Damp: What is it?

Damp occurs when a fault in the building's basic structure lets in water from outside.

There are two types of damp: penetrating damp and rising damp.

Penetrating damp occurs when water is coming in through the walls or roof, for example, under a loose roof tile, leaking pipes or waste overflow, orthrough cracks.

Rising damp is rare but if this occurs there is a problem with the damp proof course. This is a barrier built into floors and walls to stop moisture rising through the house from the ground. The usual evidence of rising damp is a 'tidemark' on the walls that shows how high it has risen. There is also a musty smell.

If you do not think the damp comes from any of these causes, it’s probably condensation.

Condensation: What is it?

There is always some moisture in the air, even if you cannot see it. Warm air contains much more moisture than cold air. You notice it when you see your breath on a cold day, or when the mirror mists over when you have a shower or bath.

Condensation is caused when moisture held in warm air meets a cold surface like a window or wall and condenses into water droplets. If this happens regularly, and is not managed, mould may start to grow.

This usually appears on cold outside walls and surfaces and in places where the air does not circulate well. The moisture created can also damage clothes, furnishings and decoration.

Condensation mainly appears during cold weather and is found on the coldest surfaces or in places where there is little or no air movement, such as in the corners of rooms, near windows, or behind furniture.

Condensation can aggravate health problems like asthma, bronchitis, arthritis and rheumatism.

What causes condensation?

Condensation usually occurs in winter because the building is cold and windows are opened less so moist air cannot escape.

Why condensation such a problem

Home improvements such as insulation to walls, draught proofing on doors and double glazing makes it easier to keep homes warm by reducing drafts and preventing heat from escaping.

However, they also prevent moisture from escaping and this makes condensation worse.

Is your damp caused by condensation?

There are a number of things you can do to reduce condensation.

Make less moisture

  • Wipe the water from your windows and sills with a cloth.
  • Hang washing outdoors to dry if you can, or put in the bathroom with the door closed and the window open or fan on.
  • Put lids on saucepans when you cook. This keeps steam in the pan and saves money on your fuel bill.
  • Don’t use paraffin or bottled gas heaters as they produce lots of moisture.
  • Burning one gallon of paraffin puts roughly one gallon of water vapour into the air which reappears as condensation on your windows or other cold surfaces.
  • Vent your tumble drier outside. If your drier is not self-condensing, make sure you put the hose out of a window to ensure the hot, moisture-filled air produced by the machine does not condense inside your home.
  • Opening a window is not enough. You can get hose kits from most electrical and DIY stores.

Increase the ventilation

  • Use the trickle vents in your window. You need a good air flow to help get rid of moisture which is produced in your home all the time.
  • Open a window when cooking and after showering/bathing. Boiling pans, hot baths and showers produce a lot of steam. Opening a window ensures this steam condenses outside rather than inside your home.
  • Keep your kitchen and bathroom doors shut when they are in use for about 20 minutes after to stop moist air getting into other rooms. When your kitchen, bathroom or other rooms are not in use, leave the doors open so that heat can spread evenly through your home.

Allow air to circulate

  • If possible, don’t put furniture against outside walls of your home. Inside walls (between rooms) are always warmer and therefore less prone to condensation.
  • Do not overfill rooms, leaving room for air to circulate.
  • Leave a gap between the wall and the furniture so that air can circulate. Avoid putting too many things in wardrobes and cupboards as this stops air circulating. There should be adequate ventilation to prevent mould growing inside. Use slatted shelves or cut a ventilation slot in the back of each shelf.

Keep your home warm

  • When moisture condenses on your walls, it makes them colder. This causes you to lose heat and increases the risk of mould growing. It then takes more energy to heat your home to a comfortable temperature which costs more.
  • Heating your home efficiently helps reduce condensation and could save money on your heating bills. Try to keep your home above 18°C (63°F). Condensation is more likely to occur if you let the temperature in your home fall below 18°C.

Insulate and draught proof

  • Insulation and draught-proofing will help to keep your home warm and reduce fuel bills, such as loft insulation, cavity wall insulation (this can be checked on request)
  • Secondary and double glazing reduces heat loss and draughts but you must ensure that there is some ventilation.

Do not

Do not block permanent vents, especially where there is a fuel burning heater in the room such as a gas fire or a cooker.


Remove mould as soon as you find it

This is important to stop it spreading and causing more damage to your home.

You can get fungicidal cleaning products from hardware/DIY stores (always follow manufacturer’s instructions) or use a good quality bleach mixed one part bleach to four parts water (remember the bleach may take the colour out).

Dry clean mildewed clothes and shampoo carpets as brushing/vacuuming can increase the risk of respiratory problems.

After treatment, redecorate using a good quality fungicidal paint to help prevent mould reoccurring. Note that this paint is not effective if overlaid with ordinary paints or wallpaper.

What to do next

Council tenants

Contact the Housing Repairs Team to arrange for a home visit by one of our technical inspectors, who can carry out a survey and advise you further.

Telephone: 01248 752 200


See more information about the council repais service for council tenants.

Private housing

Tell your landlord or agent in writing of any concerns or disrepair problems you have in your home.

If you need a more accessible version, please email so that we can help you.