Preparing for Winter – The tale of DIY Double Glazing

My current van sports an OEM single glaze side window (although I’d things differently in version 2.0). Whilst it provides great views from my “sitting room” it was both cold and resulted in a load of condensation when cooking in the winter. In an attempt to deal with this I put a layer of, essentially, Saran Wrap on the frame. Needless to say that whilst it sort of worked it was short lived.

I thought “why can’t I just make a real double glazed window?” and how hard could that be?! As it turns out it’s easy enough but can get tricky if you only have one pair of hands. The key caveat to all this that the manner in which my van was built was such that the walls already formed a frame around the outer window. Which gave the room to create the double glaze. I also did this after the fact so it was a lot harder work that it should have been!


The concept behind the idea is pretty much the same as a wood framed double glazing unit for home use and so the ingredients are much the same.

Wood Frame:

This is great to let in light when I don’t want to close off the cab section and means I can sit peacefully behind tinted glass enjoy the world without the “fish in a bowl” effect of a clear window. But being a single sheet of glass it is cold in winter and it very quickly creates condensation, over a big area, as result. So I got my thinking cap on and came up with the idea of creating a double glaze. How hard could it be? There’s actually very little out there on this. People have put actual double glazing units in as windows (although they need to be tempered glass for safety). As this was an “after the fact” job it needed a different approach. As it turns out it wasn’t such a dissimilar solution, just a lot trickier because the OEM glass that was in place is curved. The key considerations were as follows:

  1. You will need to be able to access all edges of the new pane to copiously cover it with silicone. This should be enough to be able to angle the sealant gun on to the edges of the spacer bar, otherwise it gets very messy.
  2. Because you need to secure the pain against the existing window (most likely with an extended / new frame) consider how this will be done.
  3. You will need to be able to keep pressure on the new pane to allow the silicone to set and stop it sliding south.
  4. What material will you use for the second glaze? I decided on a sheet of tinted Perspex because it was relatively light, durable, and wouldn’t break.
  5. The spacer bar frame needs to be made up (with the descant filling) within a couple of hours of installation due to the nature of the descant.

Materials you’ll need:

  • Measured sheet of Perspex of similar product (tinted for extra privacy or clear)
  • Spacer bar (I used plastic 22mm) frame
  • copious amounts of low modulus silicone (buy way more than you think you’ll need as you can always return what you don’t need). I should have had 5 tubes. Obviously have the sealant gun too.
  • Pre-cut frame for the new window size to overlap by 5mm, along with a lower sill for the pane to sit on. If you don’t have this done you risk the new pane falling out.

I’m pretty sure that the exact process for your build will be different so I’m not sure it’s so useful to describe this in exacting details but rather the steps that I took to install the double glaze, as well as the potential challenges to be aware of.

  1. The one thing that I didn’t plan for was keeping the bottom propped up during the curing process for the silicone
  2. Buy more silicone than you think you need. Most builder’s merchants will accept returns for unused tubes (it’s quite cheap anyway).
  3. Once the Perspex is installed you can measure out the wooden frame to fit. With some calculations you could probably do this before but if it’s held in place well you don’t need to.
  4. Make sure you gloop loads of silicone around the frame so that it covers the spacer bar and the edge of the Perspex, otherwise the condensation will get in.

The difference in heat loss once I installed this was night and day, and I really don’t think I could have been so comfortable in -25 degree Celsius temperatures. In the future I will use the camper specific windows as they are already double glazed and have blinds built in, but this is a great solution if you inherit a setup like mine.

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