Dealing With Condensation

Why is it a problem?

Condensation indicates a lot of moisture in the house. It contributes to mould growth and it makes houses feel colder and make them more difficult to heat.  Mould is also a trigger for asthma.

What is condensation?

Condensation occurs when water vapour is converted into liquid water.  All air contains water but the higher the temperature, the more water it can hold.  If the air temperature drops, at night for example, some of that moisture will be released when the warm air comes in contact with a cooler surface like a wall, ceiling or window pane and then droplets of water form on the surface.

How does it occur?

Our daily habits create a cycle of condensation.  Morning showers and cooking breakfast produce water.  Turning on heaters enables the air to absorb this moisture.  The house is then closed up for the day and usually cools down.  Evening activities may produce more water in the house from cooking, washing and drying clothes.

What should I do?

Ventilation is important for reducing and controlling condensation.  Fortunately is takes just a little effort to do this.  The cheapest and most effective method is to have windows open a small amount over long periods of time.  (Security concerns can be addressed through fitting security stays or fitting aluminium windows with passive ventilation and condensation channels.)

  • Externally vented extraction systems in the kitchen (range hood) or bathroom (extraction fans) will reduce moisture levels significantly 
  • If you have a clothes dryer make sure that it is ducted to the outside of the house
  • Close doors to the bathroom or laundry if large amounts of water vapour are being produced, so that it doesn’t spread throughout the house, and open the window in those rooms to allow water vapour to escape
  • Avoid unflued gas heaters (they produce a lot of water vapour and can contribute to the problem of condensation)  Dehumidifiers may assist in problem areas but they are not a substitute for adequate heating or ventilation

Portions of this fact sheet were sourced from BRANZ Bulletin 367 "Condensation" www.branz.org.nz

© Asthma and Respiratory Foundation of New Zealand (Inc.) 2005  Photocopy permission granted