Amy Hamilton Chadwick 8 Jun 2021

Condensation is a frustrating and persistent problem in Kiwi homes.

Even solutions like double glazing and ventilation systems won’t guarantee that your home will be free from wet windows in the colder months.

A truly warm, dry home needs high insulation levels, high-performance window frame and a balanced pressure ventilation system, says Nelson Lebo, Eco Design Adviser for Palmerston North City Council.

But there are only about 1,000 homes like this in New Zealand. The rest of us are living in homes that need daily management during winter to prevent condensation.


Why are our homes prone to condensation?


The history of New Zealand homes, explains Lebo, starts with classic farmhouses, bungalows and villas.

These had open woodburning fires or coal burners that act as ventilation systems. They were draughty, they were dry and they were cold. Living in a home like this, you might be freezing in winter, but dry air won’t make you sick.

From the 1960s onwards, we began replacing open fires with electric heaters that didn’t help ventilate our homes, we made draughty houses cold and damp – the worst of both worlds and a contributing factor to illnesses like asthma and chest infections. We also began building concrete slab based homes with aluminium single glazing; “It’s like living inside a ziplock bag, because they don’t breathe – there’s still a lot of these out there, especially among rentals.”

The current building code means we’re building well-insulated houses with double glazing, which makes them warm. While that’s an improvement, these homes are still relatively airtight, so moisture stays in the home and can gather on standard aluminium window frames.


How to manage your home’s condensation


Before you spend thousands of dollars retrofitting double glazing or installing a ventilation system, start by changing your habits, says Lebo: “Condensation, mould and respiratory illness are symptoms of moisture in your home. Positive pressure ventilation systems only treat the symptoms. Instead, you need to treat the cause, which is internal moisture.”

Make sure you use extractor fans in the kitchen and bathroom, avoid drying washing indoors, use a ground barrier for rising damp and remove unflued gas heaters. (More details and a video featuring Lebo here.)

For ventilation, open the doors and windows for 10 minutes each day throughout the year to flush stale air out of the home. And any remaining moisture can be removed with a dehumidifier. These are better than a panel heater in a damp bedroom – dry air feels warmer because it holds less moisture, and the appliance also generates some heat.

Together, all these steps should go a long way toward reducing your condensation. Only once you’ve done all those more affordable steps should you consider a balanced pressure ventilation system – they’re a big investment and will only work in a fairly airtight house.

“A house is an ecosystem and the only way to deal with condensation is to treat it holistically,” says Lebo. “I advocate prevention over treatment.”