picture of do it yourself secondary glazing

Do it yourself secondary window glazing

You simply can’t have an energy efficient home unless you do something about single glazed windows, especially if they have standard aluminium frames. Aluminium is excellent at conducting heat so if it’s warm inside your home and cold outside, that warmth will be moving through those aluminium frames and escaping outside in a jiffy. As for the single pane of glass- that also transmits heat rather easily and if you add up all the area of windows in your home, that’s like having lots of  large holes in your blanket and expecting to stay warm.

The retrofit solutions are replacing all the windows with double glazed units with thermally broken frames, installing secondary glazing or installing thick curtains with pelmets to trap a still layer of air between the curtain and the glass.

Let’s talk about secondary glazing: there are companies who specialise in this and they do an excellent job. We routinely recommend Magnetite and Eco-Glaze. There are also do it yourself options: Clear Comfort window film and you can also install your own second layer of acrylic sheet. Here’s how I did it at a unit we own.

  1. measure the window size from frame to frame eg 1800*1800mm
  2. Order acrylic sheet cut to size, allowing for a 0.2% gap for expansion and some wriggle room eg 1795*1795mm. There are several companies easily found online who offer this service. Small windows could use 3mm thickness and larger ones, 4mm.
  3. I bought aluminium profile (you could also use a timber bead) in “L” shape to support the secondary sheet and screwed that in position around all 4 sides of the frame being careful to keep it all in the same plane. Try to keep the gap between the existing glass and the new sheet around 12-15mm for energy performance but if you want better acoustic performance the gap should be more like 50mm.
  4. For small windows eg in toilet or laundry eg 1000*1000mm or less, the acrylic sheet can be held in place by sticking magnetic tape (part A) to the aluminium strip and (part B) to the edges of the acrylic sheet. Once in place you’ll need a suction cup to pull it off again.
  5. For larger windows like our example 1800*1800mm, the magnetic tape is not strong enough to hold the acrylic sheet in place and you’ll need a second timber bead attached over the top of the sheet to hold it.

In the image of the bathroom window you can see the aluminium bead, the magnetic strip and the acrylic sheet. If the window behind ever needs to be opened, the acrylic is easily lifted away by using a small suction cup that I bought at a large chain hardware store.

Another useful tip- you may have a window where it is appropriate to drill holes in the acrylic sheet to screw it directly onto a timber frame. Remember to allow for expansion so make your hole a bit bigger than the screw and use a blunted drill bit to avoid splitting the acrylic sheet. You can blunt the drill bit by drilling onto a piece of concrete briefly. Let us know how you go with your DIY window treatments!