How to join $100 double glaze craze

KATH Bee is double glazing her own windows this year to keep out the cold . . . for under $100.

To DIY double glaze her home in Motueka, at the top of the South Island, Bee will need to stick a thin plastic film to clean window frames around the house then use a hairdryer to make sure it is stuck tight.

A pocket of air is trapped between the plastic and the window, reducing heat loss and condensation build-up.

‘‘We’ve just moved down to the country and I kinda realised how freezing it is out here,’’ Bee said.

To cover half the windows in Bee’s house it would take about 50 metres of the film and cost about $50 from plastic packaging company Accolade Packaging, not including the double-sided tape.

Energy Efficiency & Conservation Authority (EECA) Energywise senior technical adviser Christian Hoerning said DIY window insulation was just as effective as permanent double glazing on most windows.

Temporary double glazing could roughly halve the heat lost through windows, reduce condensation and ‘‘significantly’’ reduce the heating bill, he said.

There was a range of products available from hardware stores but it would cost most people about $20-$50 to cover the main lounge and kitchen windows of a house.

According to Consumer New Zealand, self-fitted temporary glazing comes in at around $7.50 a square metre. For a 20 metre square lounge, with 8 metre square of windows this would work out at about $60.

Hoerning said this method would work on all windows with wooden frames and clean paint.

DIY window insulation is not for everyone.

While you can still see through the windows it can cloud the view and makes cleaning tricky.

According to a 2010 study by a Victoria University Masters of Building Science student who measured retro-fitted secondary glazing systems, the thin plastic film was the most cost-effective double glazing option, mainly because of its low initial price.

It paid for itself in heating cost savings within one year in Wellington, Christchurch and Dune- Keeping out the cold: Kath Bee, right, inspects a DIY double glazed window at her friend Janice Schofield Eaton’s home. din, while payback for more permanent forms of secondary glazing could take up to 30 years, the study found.

Hoerning said other forms of secondary glazing, such as magnetically-attached acrylic sheets or retro-fitted thermalaluminium framed windows were more permanent. It could cost thousands of dollars, rather than $100, to install more permanent forms of window insulation.

Hardware store chain Mitre 10 sells DIY multi-window insulation kits. A spokesperson said sales of its window film products during the past financial year were at their highest ever and demand was expected to continue increasing. ‘‘As it is a temporary and cheaper alternative to glazing, it doesn’t do as good a job as actual double glazing but does certainly make a difference,’’ the spokesperson said.