Double glazed windows

What do you think of the retrofitted double glazing that’s being widely advertised at the moment? Does it work? Is it a fad? And are the advantages worth the cost? We can’t afford to replace our single glazed windows with double glazed ones, but we might be able to improve our existing windows.

Having double glazing retrofitted – in other words turning your single glazing into a form of double glazing – isn’t a fad and it does work. Whether it’s worth the cost depends largely on the climate you live in. Independent research done through the Building Research Association of New Zealand (Branz) concluded that it’s probably not worth doing if you live in or around Auckland, but if you’re further south, especially around Christchurch and Dunedin, it’s a good investment.

Several types of retrofitted glazing systems were tested – double-sided adhesive tape-attached, heat-shrinkable thin plastic film, magnetically attached acrylic and aluminium-framed sliding sash. All of them significantly increased what the boffins call “thermal resistance”.

But the option that easily came out best was called aluminium-framed, sliding sash, low emissivity (low-E) secondary glazing. It’s more expensive, but its thermal performance was nearly twice as effective as the others. It also out-rated the other options on a cost-benefit basis.

This test was in 2010, so other products may be on the market. Phrases such as “low emissivity” make me nervous, physics not being my strength. But you can find out more from the government’s Energywise, Branz or the Window Association of New Zealand (Wanz). They’re the experts.

Do you have a consumer question for Kevin? Email consumer@nzww.co.nz, or post to Weekly Consumer, PO Box 90119, Victoria St West, Auckland 1142.