Controlling condensation

Winter condensation is a widespread problem. In winter we spend more time indoors, creating moisture from cooking, cleaning, washing and even breathing. When we're out of the house we leave it closed up for security.

Insulation adds to the problem. We trap the heat of living areas by keeping doors shut and using heavy curtains and carpets.

This all comes at a price. Warm air holds water better than cold air. Because it's sealed in, the moisture builds up then condenses on cold surfaces such as windows and walls. But who wants to throw open the windows and replace all that lovely warm (wet!) air, heated at some expense, with a wintry blast from outside?

The solution

The solution is simple – better ventilation. Making it happen is less simple. If you're living in a draughty old Victorian villa, you shouldn't have too much of a problem with ventilation. But modern houses are much more airtight, so natural ventilation is minimal.

Extra heating is part of the solution, combined with water extraction near the sources. Rangehoods intercept steam from the kitchen; extractor fans are effective at drying out bathrooms. You could also consider a dehumidifier. While these can help control condensation, they’re expensive to run (up to $2.50 a day), often noisy, and must be run constantly. With a dehumidifier you are controlling the symptoms and not dealing with the problem. While not the ideal solution, dehumidifiers have their place.

An automatic ventilation system is a better way of controlling condensation. Whichever way you attack the problem, remember it's even more effective if the amount of water released into the air is reduced.
 

Sources of moisture

Stopping the sources

If you have not already attended to these:

• Fit extractor fans over the cooktop or stove, and in the bathroom. They must be ducted to the outside.
• Always use close-fitting lids on pots when cooking.
• Vent the clothes dryer to the outside.
• Close doors when cooking, showering or using the dryer, to limit the spread of moist air.
• Avoid using unflued gas heating.
• Limit the number of pot plants in the house.
• Check that the ground under the house is dry. If it's wet, cover with polythene (if this is feasible), taping the joints, and ensuring a tight fit around piles. Check that drainage systems are diverting water away. 
• Fix any leaks in the roof or around windows.
• Remove open vented downlights or replace them with new downlights that don’t leak your warm damp air into the ceiling.

Check your ceiling insulation

If you don't have any insulation, get this installed first. If existing insulation has become dislodged, compacted or wet through roof leaks, it won't be fully effective. It may even be inadequate for your climate. Fix all insulation problems before considering how to improve your heating and ventilation.

Building code requirements

The building code has minimum requirements for ventilation: all the air in your house should be changed every three hours. It says the air in kitchens should be changed every hour; in bathrooms every two hours. To achieve this, the code suggests extractor fans in kitchens and bathroom – and open windows elsewhere – to bring in fresh outside air.

But you won’t want to leave windows open while you are away from home or overnight, for security reasons. An option is to have trickle vents inserted into your windows. These can have insect screens and shutters to control pests and the amount of air flow. Examples are at www.joinerydev.com and www.woodman.co.nz.