DIY front door secondary glazing/ insulation

The house is a 1920s detached house, originally with timber framed windows. These were replaced in the mid 90s with UPVC double glazed units, however the front door was left single glazed, presumably for aesthetic reasons as it had a stained glass panel and decorative semi-frosted surround windows.

We are aware there is a lot of heat loss though the single glazing, as well as via the rebated surrounding lower panels and the lower panels of the door itself.

We considered various secondary glazing DIY systems, however as this was important cosmetically, we decided to use the Superglaze system. Unlike magnetic fixings or clip systems, there are no visible screw fixings.In the image below you can see Superglaze on the central stained glass window as well as the one each side and the three windows above. It made sense both cosmetically and financially to use one piece to cover all three at the top.

Front door with secondary glazing

This thermal image below was taken with the glazing not fitted to the pane to the right of the door. It seems to make a huge difference!  Double glazed windows in the property were reading 13.5º so it seems the secondary glazing performance at 11º – 12º is not far off that.Front door thermal image

Here you can see a nearby double-glazed window at the same property. Photo taken about the same time:

Double glazed window nearby


How Superglaze works

  • The Superglaze strips consist of a base section and a cover strip which clips into place and hides the screws.
  • They are cut to length (with the cover strip in place ) with mitred ends to form four sides of a frame for the glazing. Cover strips removed for fixing
  • The glazing is a push fit into the base section
  • This is then screwed in place over the existing window frame.
  • The cover strip clips over and very neatly hides the screws.




Tools required

  • Take measure
  • Hacksaw
  • Mitre block
  • Screwdriver
  • Drill or bradawl for screw pilot holes

The system is easy to fit, although I found a couple of things in the instructions that could do with better clarification. However the support from Martin at was amazingly helpful and he took on board my points about the instructions and will be updating them.

Tips and Hints for installation

Masking tape to hold cover strip in place
  • However experienced you are at DIY, the more accurate the mitres are the better. When you cut the mitres, the cover strip should be in place, however it is possible for it to slip lengthwise. To stop this use some masking tape to hold it in place.
  • As you will be doing this with four strips per panel you may also want to mark (on the back) which cover goes with which base section as it’s easy for the length to be  slightly out by 0.5 of a mm or so. This is not a big problem for final installation (see below), but it will look best if each cover strip exactly fits its case section.
  • After cutting the mitres, you may be tempted to use a file to clean them up if there are burs left from the hacksaw. If so be very careful you don’t file away too much. It’s probably better to use a very fine sandpaper being careful to only sand the side, not the top.
  • The instructions mention that each Superglaze strip is 23mm longer than the panel. This is actually 2mm longer than it technically needs to be if were to push each panel all the way into the base section. What the extra length means is that they do not quite go all the way in. The advantage of this is that if any one (or more) of your strips is just a tiny tad too short, it is not a disaster. as you have some leeway to push the panel in further to take up the error.
  • One thing to please bear in mind, make sure you clean the inside of the existing window first! Likewise the polycarbonate (however it’s not a disaster to take down, just a matter of removing the screws so a 5 or 10 minute job.
  • Keep the protective film on until final installation, so when fitting the Superglaze strips you can peel it back or remove a cm from the edge rather than removing all the film. Leave the rest there until you actually fit to the window which makes cleaning much easier.
  • It is important for secondary glazing that the seal is airtight. Before installing we sanded some slightly rough bits where the door had been badly decorated but you can also stick some old fashioned type foam draft excluder between the Superglaze strip and the frame.

Polycarbonate thickness

We also got good advice about the thickness. He mentioned that for smaller (or narrower) areas such as the top window, 3mm thick was sufficient, but 4mm would be better for the larger area as it would be more rigid. Will the 4mm provide better insulation than the 3mm? Watch this space as we will be using the thermal image camera on this to see the difference between the different thickness of secondary glazing, as well as the improvement over the single glazing. The difference between single glazing and the polycarbonate secondary is very noticeable already as the hallway feels better, and just touching the surface of each you can feel how much colder the single glazed glass feels. The polycarbonate itself is UV protected and very strong (good for security), so can also be used externally.

This is by far the best looking secondary glazing system I have seen: it is perfect for this type of application where you do not need to open the windows. (Note that if you do have opening windows but no longer need to open them, you can paint then shut and still use Superglaze). If you need to remove it for any reason it would only take a few minutes to remove the cover strip and unscrew. It is quite an easy DIY job, however you need to measure accurately and I would recommend you practise sawing the mitres on a piece of spare base section strip.

Our plan is/was to fit double glazed sealed units into the rebates of the left and right windows, however after seeing how good the Superglaze looks, we may abandon that idea and use Superglaze there as well. One problem with fitting double glazed units into the rebates would be that it would need framing, and so end up with smaller area of visible window which may look out of proportion. With Superglaze this would not be an issue.

Insulation for the wooden door surround rebates

In addition to the secondary glazing, it occurred to us that the door panels and rebates in the door surround were possibly areas that could also do with some insulation. There is only about 10mm of timber between the heated hallway and the cold outside.

From an aesthetic point of view this isn’t something you can just add 100mm of Celotex to, but we thought perhaps something can be done to make at least some kind of improvement. The obvious solution would be Aerogel as it has a really good insulation factor even when very thin, but until the cost comes down we though we’d look at a cheaper solution. We are also very aware that the door is in dire need of redecorating, so something easily removable would be ideal.

We happened to already have some polyethylene sheets about 10mm thick. I had bought this to form a shaped inside to a case that was needed to carry some precision and fragile instruments as it is a good shock absorbing material. This is sometimes called closed cell foam and one thing I discovered is that it also has a fairly decent insulation value

It is not the same as the more common expanded polystyrene which crumbles easily and is not flexible. Nor is it like the mattress type of foam which is soft and spongy. I think it’s the same stuff they make hot water pipe lagging from and it is great for this purpose as it is quite flexible but not too soft, and very easy to cut (with a Stanley knife)

This is quite easily available (it is often sold for exercise mats but seems to cost more when advertised for that use). I had to hunt around to find a good price.

The rebated panel to the side of the doors are about 25mm deep, so the plan was to cut some polyethylene to size and then just glue it into the rebates.


However I actually cut it 1mm too big all the way round, which proved to be a very fortunate accident as it just fits very snugly in the rebate with no need to glue, although it is also available with a sticky back.

You could probably also use polystyrene or sponge but this stuff seems to be better suited because polystyrene may crumble and spongy foam would probably have to be glued in. The plan will be to decorate it (it can easily be covered with lining paper and painted), but until we stop procrastinating it will do for now.

polyethylene in rebate

  • Tools required: Stanley knife, tape measure, straight edge
  • Time :7 minutes
  • Cost: approx £10 for two rebates

Watch this space: we will be trying the thermal imaging camera on this to see how it performs.

Polyethylene foam




close up


Share: Facebooktwitterredditpinterestlinkedinmail

3 thoughts on “DIY front door secondary glazing/ insulation”

  1. Tks for the info, interesting and helpful we have a beautiful wooden door with stained glass we don’t want to change it to a pVC door so your tips and advice could help our hall a warm place instead bloody freezing

  2. Have you got a thermal image pre and post installation? Overall it looks very neat and if it has been successful would install and show to others.

    • Not yet George. I will need to remove one of them and then take the image. probably best to do it with one of the left/right panes as this will show the difference better than low/high as it’s obviously always warmer higher up.


Leave a comment