Winter woes of condensation and mould

Whether you are a tenant or an owner occupier, in cold weather it can be difficult to avoid condensation and the tell-tale rivulets of water running down the inside of windows or walls, especially in bathrooms and kitchens.

Condensation is usually the result of occupancy, when even breathing will deposit damp vapour into the atmosphere, although occasionally it can be the outcome of a damp wall or similar issue in the building.

At its worse, condensation, or a build-up of moisture in the air, can lead to mould – a living organism or fungus made up of spores, that can be detrimental to health, possessions and even the fabric of a building. So, it is vital to keep on top of any issues arising from condensation, and treat as soon as you become aware that there is a problem.

Moisture is always in the air, even if you cannot see it. When there is a difference of temperature – say between rooms, or inside and out – the air cannot hold all the moisture and tiny drops of water form. This is condensation. You notice it when you see your breath on a cold day, or when the mirror mists over in the bathroom.

It can appear on cold surfaces and in places where there is little movement of air. Look for it in corners, on or near windows or on walls behind furniture. In bad cases it can also occur inside cupboards and wardrobes. The problem can be worst on north-facing walls, and on walls exposed to the prevailing wind (because these are typically colder). Black mould often starts to form if there is a persistent problem.

Obvious causes of condensation can be as simple as a lack of ventilation and changes in temperature, although sometimes other problems are present and will need to be investigated. Condensation is often characterised by mildew and by areas of black mould, particularly in colder areas.

Fighting condensation:
You will need to take appropriate and the correct steps to deal with the causes of condensation, but you can start immediately to reduce the problem:

Begin with wiping down the windows and sills every morning and then wring out the cloth rather than drying it on a radiator. You can also try to ensure that steam from the bathroom and kitchen doesn’t spread round the property. Close internal doors and open windows to let any steam out.

Condensation channels and sponge strips can be bought at DIY shops. They are fitted to windows to collect the condensation and thus help prevent window frames from rotting and avoid damp forming under sills. Care must be taken to fit these devices properly.

Fighting mould:
First treat any mould already in your property. If you then deal with the basic causes of condensation, mould should not re-appear.

To kill and remove mould, wipe down walls and window frames with a fungicidal wash which carries a Health and Safety Executive ‘approval number’, following the manufacturers’ instructions precisely. Dry-clean any clothes affected by mildewed, and shampoo carpets. Disturbing mould by brushing or vacuum cleaning can increase the risk of respiratory problems as it disperses the spores that make up the mould.

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

How to avoid Condensation
These four steps will help you reduce the condensation in your home:

1. Produce less moisture
Some ordinary daily activities produce a lot of moisture quickly.

  • Cooking: To reduce the amount of moisture, cover pans don’t leave kettles boiling.
  • Paraffin and portable flueless bottled gas heaters: These heaters put a lot of moisture into the air – one gallon of gas or paraffin produces about a gallon of water vapour. Try to find an alternative means of heating such as oil filled electric heaters, which tend to be less expensive to run, but do your research before buying.
  • Washing clothes: Put washing outdoors to dry if you can, or put it in the bathroom with the door closed and the window open or extractor fan on. If you have a tumble-dryer make sure you vent it to the outside (unless it is the self-condensing type). DIY kits are available for this.

2. Ventilate to remove the moisture
You can ventilate your home without making draughts.

Some ventilation is needed to get rid of moisture that is being produced all the time, much of which comes from breathing so keep a small window or a trickle-ventilator open when anyone is in the room.

You need much more ventilation in the kitchen and bathroom when cooking, washing up, bathing or drying clothes. This means opening windows wider using a humidistat-controlled electric fan (these come on automatically when the air becomes humid, and are cheap to run).

Close kitchen and bathroom doors when these rooms are in use, even if your kitchen or bathroom has an extractor fan. A door-closer is advisable. Doing this will help stop the moisture reaching other rooms, especially bedrooms, which are often colder and more likely to suffer condensation.

Ventilate cupboards and wardrobes. Avoid putting too much in them as that stops air circulating. Subject to ownership (whether you are a tenant or owner), cut a ventilation slot in the back of each shelf or use slatted shelves; cut ‘breather’ holes in doors and in the back of wardrobes. Leave space between the back of the wardrobe and the wall; put floor-mounted furniture on blocks to allow air underneath. Where possible, position wardrobes and furniture against internal walls (walls which have a room on both sides) rather than against outside walls.

If you replace window units at any time, make sure that the new frames incorporate trickle-ventilators. You should also ensure that some openable part of each window is at the top so as to avoid ‘dead-spaces’ that will not get adequate ventilation.

3. Insulate and draughtproof
Loft, cavity wall insulation and draughtproofing of windows and outside doors will help keep your home warm and you will have lower fuel bills too. When the whole home is warm, condensation is less likely.

When draughtproofing:

  • do not block permanent ventilators;
  • do not completely block chimneys (leave a hole about two bricks in size and fit a louvred grille over it);
  • do not draughtproof rooms where there is condensation or mould;
  • do not draughtproof a room where there is a fuel-burning heater (for example, a gas fire) or cooker;
  • do not draughtproof windows in the bathroom and kitchen

In a house or bungalow, insulating the loft is a cost-effective way of cutting heating costs. Remember to draughtproof the loft-hatch but do not block the opening under the eaves.

Cavity-wall insulation is an effective way of cutting heating costs. However, before deciding on this route, talk to your local building inspector as building regulations approval is needed.

Secondary or double glazing windows reduces heat-loss and draughts, but ensure that there is sufficient ventilation. However warm a building is, locking all moisture inside it will cause high humidity and potential problems.

4. Heat your home a little more
In cold weather, keep rooms warm enough to avoid condensation by maintaining low background heating all day, even when no one is at home. This is very important in flats and bungalows and other dwellings where bedrooms are not above a warm living room. So, if possible, install a small heater with a thermostat in each bedroom (but do not use a paraffin or flueless bottled gas heater for this purpose). The thermostat will help control heating and costs.

Dehumidifiers help dry out damp in newly built houses and can also help reduce condensation in warm rooms with a lot of moisture, but they are of little use in cold damp rooms.

Points to remember

Produce less moisture:

  • cover pans
  • dry clothes outdoors
  • vent your tumble dryer to the outside
  • avoid using paraffin or flueless bottled gas heaters

Ventilate to remove moisture:

  • ventilate whenever someone is at home
  • increase ventilation of the kitchen and bathroom when in use and shut the door
  • ventilate cupboards, wardrobes and blocked chimneys


Insulate and draughtproof:

  • insulate the loft
  • draughtproof windows and external doors
  • consider cavity insulation
  • consider secondary glazing
  • find out if you are eligible for a grant or other help


Heat your home a little more:

  • if possible, keep low background heat on all day
  • find out about benefits, rebates and help with fuel bills

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