Lifestyle: Yankee thrift meets Kiwi ingenuity

DIY double-glazed window in our bathroom.

Over the past month I have tried to enliven the discussion of passive solar design with certain musical references: Aretha Franklin, The 5th Dimension, and the incomparable Neil Diamond.

But this week I got nothing.

As important and ubiquitous as insulation is, no one appears ever to have written a love song about it. For any aspiring singer/songwriters out there, this may be your niche.

Insulation, in a nutshell, is about slowing the rate of heat transfer. Sometimes this is called "thermal resistance" and is measured by R-value. Anyone who has purchased insulation for their home will be familiar with R-value, but may not understand it completely. I often describe it this way:

Think of R-value as "Resistance to heat flow" - anything that slows heat energy from flowing through it: a sleeping bag, an eider down, a Swandri, fibreglass batts, double-glazed windows, a wool blanket.

Another way I describe insulation is trapped air. This description suits those materials listed above as well as something I wrote last week:

Water and anything that sinks in water has good thermal mass, but anything that floats in water acts more as insulation. The faster something sinks in water the more thermal mass it has, and the higher something floats in water the more insulation it probably provides. Think polystyrene.

Picture, if you can, the inside of a sleeping bag or eider down: natural or artificial fibres that fluff up and create lots of tiny air pockets.

Now picture a double-glazed window, or look at the picture I've included with this column. The advantage with this example is that you can easily see the trapped air because it is between two panes of glass. With double-glazing, it is not the extra piece of glass that provides significant insulation: it is the air trapped between the two panes.

From this perspective, plastic DIY double-glazing is just as effective as professionally manufactured glass double-glazing. The picture I've included is actually an example of glass DIY double-glazing in our bathroom, which consists of a large, second-hand aluminium window, wooden battens serving as spacers, and safety glass as required by the building code. This is certainly an unusual approach to double-glazing, but it has performed well for us at a fraction of the cost of buying a new window of comparable size.

Another unusual but cost effective approach to trapping air that we used in our renovation was hanging a Trade Me version of what would be called a storm door in North America. The picture I've included should be easy to interpret: one glass door opens inward and one glass door opens outward. The space between doors (when closed) is the "trapped air" that insulates our home while still letting free sunlight energy through. This is where Yankee thrift meets Kiwi ingenuity.

Nelson Lebo consults businesses, schools, and home owners on all aspects of sustainability - email: theecoschool@gmail.com or phone 06 344 5013 or 022 635 0868.