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Retrofit double glazing

In May 2007 I experimented with double glazing one of my south side (that's the cold side in New Zealand) windows. Here's what I did:

  1. remove window
  2. board up window
  3. remove old glazing
  4. strip back old paint
  5. route out window frame for deeper double glazed unit
  6. paint
  7. insert double glazed unit into window frame
  8. seal in place with non-acidic silicon
  9. fix in place with wood beading
  10. putty any gaps
  11. paint
  12. re-hang window
  • $110 per 500 x 1000mm double glazed "unit"
  • time consuming
  • seems to work well (no condensation when compared with single plan glass)

I bought my double glazed unit from UltraGlass in Seaview, Lower Hutt (map). You should be able to get your own from most large glazing companies.

You need to specify the width and height (as per a normal sheet of glass, plus the size of the spacer. I had the options; 8, 10, 12, 14, 16, 18mm and so on up to 24mm (I think they went that far). I went for the 14mm - which resulted in an over all thickness of 23mm (4mm glass + 14mm spacer + 4mm glass + 1mm glue). That was about as thick as I could comfortably fit into the existing window frame.

What's the most efficient spacer to have? Here's a snippet from Wikipedia:

The gap is usually 12mm to 20mm thick. Within this range, the thickness does impact the insulating properties substantially, but smaller gaps have greater heat conduction through the air or other gas, and larger gaps allow more convection within the space leading to higher convective heat loss. A 16mm air gap is often considered the optimum thickness for air although this depends on many factors such as the size of the window, the temperature difference between the two panes and whether it is vertical.

I didn't go for low-E glazing - because it was almost twice the price.

Retrofit plastic acetate

I also experimented with cheap "window warmers" plastic double glazing. I bought a 3M 5 window kit:

  1. apply double sided tape to outer edge of window frame
  2. cut plastic to shape (with 10mm to spare)
  3. stick plastic on frame
  4. heat with hair dryer to form a tight surface
  5. trim excess
  • $2 to $5 per window
  • seems to work as well as a double glazed unit

You can buy it from:

Bubble wrap

  1. cut bubble wrap to size (try to fit as accurately as possible)
  2. spray glue onto bubble side of bubble wrap
  3. apply to inside of window
  • $1 per window, plus spray on glue
  • not as good as the above options so better try them

See also:

Felix's Do it yourself Secondary Glazing


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Page last modified on 21 September 2008 at 01:09 PM