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Why Do My Windows Weep?

Condensation is a symptom of dampness in many New Zealand homes, occurring where moist, warm air meets a cooler surface. Windows become wet on the inside and appear to “weep”.

Dampness, condensation and the resulting mould growth can damage paint, furnishings, aggravate allergies and cause those living with them to become sick.

What can I do about it?

Condensation on windows is a symptom of:

  • inadequate heating
  • inadequate ventilation
  • inadequate insulation

Tackle these three causes and you will greatly reduce or eliminate weeping windows. Start with good design. If you’re designing a new house or making renovations, make sure your large living area windows face north to catch the sun during the day. Keep the windows on the southern (cold) side of the house smaller.

Warm it up

Install clean, efficient heating that is sized correctly for your home and can cope with the coldest winter nights. Clean-burning pellet burners, heat pumps and flued gas heating are all good choices and, correctly sized, should provide warmth for your whole home. A vented heat distribution system or underfloor heating are good ways to ensure even large homes are evenly heated.

Ventilate your home

Moisture in the air comes from a number of sources within the home. Bathing, cooking, laundry – even breathing – generates a huge amount of moisture every day. Houses these days are designed to be nearly airtight. They’re easier to keep warm, but this means that moisture can’t easily escape by itself.

When at home, opening windows will ventilate and dry your home. For those whose homes are closed up every day during the work week, passive ventilation (built into some types of window units) or mechanical (including heat exchange) ventilation are the best ways to create a dry, healthy, comfortable home.

Upgrade insulation in joinery

Your walls, floors and ceiling need insulation to keep warm air in and cold out; your windows are no different. Double-glazing will always improve insulation, but heat escapes through the frames of windows too. For both new homes and renovations, thermally improved joinery is your best option for preventing heat loss through your windows.

This joinery separates the metal frame to prevent the metal being such an effective conductor of heat. Thermally improved windows with double glazing are the ultimate solution. The Thermal Series is a good example of what is available.

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