Damp and mould

What is condensation?

There is always some moisture in the air even if you cannot see it. The warmer the air the more moisture it will carry, and if the air gets colder, it cannot hold all the moisture and tiny drops of water appear.

Condensation occurs mainly during cold weather whether it is raining or dry.

Where does it occur?

It appears on cold surfaces and in places where there is little movement of air.

Look for it in corners, on or near windows, in or behind wardrobes and cupboards. It often forms on north-facing walls.

Is it condensation?

Condensation is not the only cause of damp. It can also come from:

  • leaking pipes, wastes or overflows
  • rain seeping through the roof where a tile or slate is missing, spilling from a blocked gutter, penetrating around window frames, or leaking through a cracked pipe.
  • rising damp, due to a defective damp-course or because there is no damp-course.

These causes of damp often leave a tide mark. If your home is damp for any of these reasons it may take weeks of heating and ventilation to dry out. Hiring a humidifier will help. If you do not think the damp comes from any of these causes then it is probably condensation.

How to avoid condensation

Produce less moisture

  • cover pans and do not leave kettles boiling
  • avoid using paraffin and portable flueless bottled gas heaters as these heaters put a lot of moisture into the air
  • dry washing outdoors on a line, or put it in the bathroom with door closed and the window open or the fan on
  • vent any tumble dryer on the outside unless it is the self-condensing type. DIY kits are available for this

Ventilate to remove moisture

You can ventilate your home without making draughts.

  • keep a small window ajar or a trickle ventilator open when someone is in the room
  • ventilate kitchens and bathrooms when in use by opening the windows wider. Or better still, use a humidistat controlled electric fan. These come on automatically when the air becomes humid, and are cheap to run
  • close the 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, as this will help prevent moisture reaching other rooms, especially bedrooms, which are often colder and more likely to get condensation
  • ventilate cupboards and wardrobes. Avoid putting too many things in them as this stops the air circulating. Cut a ventilation slot in the back of each shelf or use slatted shelves. Cut 'breather' holes in doors and at the back of wardrobes, and leave space between the back of the wardrobe and the wall. Where possible, position wardrobes and furniture against internal walls
  • if you replace your window units at ay time, make sure that the new frames incorporate trickle ventilators

Insulate, draught proof and heat your home

Insulation and draught proofing will help keep your home warm and will also cut fuel bills. When the whole home is warmer, condensation is less likely.

  • insulate your loft. Remember to draught proof the loft hatch but do not block the opening under the eaves
  • consider cavity wall insulation. Before deciding though, you should talk to your local building inspector as building regulations approval is required
  • consider secondary and double glazing of windows, to reduce heat loss and draughts, but you must insure that there is some ventilation
  • in cold weather, keep low background heating on all day even when no one is at home

Some words of warning

  • do not block permanent ventilators
  • do not completely block chimneys. Instead, leave a hole about two bricks in size and fit a louvred grille over it
  • do not draught proof a room, where there is a cooker or a fuel burning heater, for example, a gas fire
  • do not draught proof windows in the bathroom and kitchen

First steps against mould

  • first treat any mould you may already have in your home. If you then deal with the basic problem of condensation, mould should not reappear
  • to kill and remove mould, wipe down walls and window frames with a fungicidal wash, which carries a Health and Safety Executive's 'approval number'. Follow the manufacturer's instructions precisely. Dry-clean mildewed clothes and shampoo carpets. Disturbing mould by brushing or vacuum cleaning can increase the risk of respiratory problems
  • after treatment, redecorate using a good quality fungicidal paint to help prevent mould recurring. Note that this paint is not effective if overlaid with ordinary paints or wallpaper

The only lasting way of avoiding severe mould is to eliminate dampness