DIY Double Glazing

Double Glazing is expensive and retrofitting even more so. Using basic principles of keeping a layer of air in between 2 layers of glass, I decided to use perspex as the indoor layer and keep that on our windows with magnetic strips. Perpex has good low E properties, is relatively inexpensive, shatterproof and does not break as easily as glass.

Step 1 Materials and measurements required

1. Measure your window - glass only. Get the sheets from a glass/ acrylic dealer or wholesaler. Usually they will cut to measure without extra cost.
2. If your window is "fixed", ie does not open, then the extra insulating layer can be bigger than the glass by a margin of about 1cm all round, giving better "seal" and less window frame surface exposed to leak heat and attract condensation
3. If your window has latches - the extra insulating layer has to be exactly the same size as the glass - which means you will lose 1 cm of see through window round the perimeter once the magnetic strips go on.
3. Materials required:
- perspex (acrylic) 2-3mm thick, optical / window quality - do not remove paper backing till ready to mount on window
- self adhesive magnetic strips 1cm wide - measure / calculate the perimeter of the windows to get an estimate of how much to buy
- craft scissors

Comments

[slysimon]

From memory, when I studied insulation at Uni: This will definitely work. We call it secondary glazing rather than double glazing. If you increase the gap between the original glass and your perspex you will increase the insulating properties as it will take longer for the heat to migrate to the outside. Three layers is always better than two. But be careful: Double the insulation and you only increase the efficiency by 50% not 100%.

[herb21]

Increasing the air gap only helps to a point, there tends to be a threshold after which it lessens the efficiency as the convection increases at that point.

[slysimon]

Very true. Can't remember off hand what the magic number is, I would think an inch or maybe two is okay, after that a third sheet of perspex would be more useful.

[Wille B]

Hey, just a little aside. Moisture between the panes can be a pain. An old studio build trick is to put rice in between the panes to absorb the moisture. It has been 100% effective in my practice.

Feel free to message me about this if you want more info!

[whodatrat]

I was wondering how thick the air gap is. Does this technique produce any sound attenuation? Thank You Appreciated the instructable.

[shanitan]

the airgap for our window is about 2-3mm - sound insulation is only so-so

[trailleadr]

I'm not looking to take anything away from this 'ible, as you did a fine job. However dual paned units are made with an airtight barrier between the glass. In addition the glass is heated prior to being sealed so that the air inside expands. Once heated and sealed the air inside contracts as it cools, and actually forms a pseudo vacuum as it as not as dense as the ambient air. It's actually the lack of air, or not as dense air that helps make dual pane glass a good insulator. I only mention this because I think it would be a disservice to others looking to replicate this and expecting the same performance as a dual pane insulated window.

[shanitan]

I agree with you completely, there is no intention to replicate a real double glazed window, but to add a layer of air in between the glass and perspex. the air plus perspex becomes another layer of insulation pretty much like a thick insulating curtain, but still allowing you to see out and get some light in :)

[kemp1]

Hi Shanitan,
Your process for retro fitting some form of doulble glazing looks good and should work in princlple. One question that I have is how do you allow for the acrylic perspex to move/expand when exposed to sun and heat. You have one of the magnetic strips double taped to either the glass/aluminium, and another taped to the perspex. How do you allow for movement of the sheet with out breaking the seal?
Cheers

[XxZombiexX]

As you said, these are not meant to replicate an actual double pane window, but just to add a bit to trailleadr's comment regarding actual ones, we used Argon gas when I worked at a window factory to fill the space between the panes.  I didn't learn why argon specifically, except it is inert.  
Either way, I def would like to try this at my apt.  Thanks!

[slysimon]

I think they use argon gas because you then don't get any condensation in between the glass.

[trailleadr]

I can't speak for all window manufacturers, but our glass went through a cleaner and hot air dryer and into a climate controlled room for assembly. From there it was passed into a heated rolling press that would firmly press the two panes onto the adhesive spacer. The newly formed double pane would exit screaming hot and be promptly sealed. There was never any need to worry about moisture unless a unit had the chance to cool prior to being sealed. If you ask me the argon is a gimmick.
But then I was just a glass cutter, not an engineer so I could be wrong about argon and it's presence in double paned windows. :)

Personally I prefer my argon in a bottle for my welder not in my windows. :p

[slysimon]

:) Excellent, well said. It could well be a gimmick. Or it could just be an cheaper, easier, and perhaps not such a good way, of achieving the same results as your process.

[nillo]

I think this would actually be considered an indoor storm window. It will definitely help.

[PaloAltoMark]

I have single pane glass throughout the house. Can you give me some indication of the performance of this solution?

[shanitan]

yeah, I have single pane throughout as well. Will be fitting the perspex onto the new bedroom once that has been renovated with new bathroom ensuite, so will let you know then. That's the coldest room in the house (south facing) so if it makes a diff, we'll know. As for our electricity bill, it has come down a bit, but again we have only been in this house for 2 months and 1 month of winter, it's hard to comment. To digress, ever since we added a ceiling fan and put it on reverse, we are using less wood in our woodstove in the living room.

[T3h_Muffinator]

Awesome idea! I'm curious to see if you could pull a vacuum in that thing (assuming you seal it with silicone or something better than magnetic tape).

[shanitan]

not sure, may be possible... but havent tried

[shanitan]

Reason for using mag tape is the possibility of removing it and not having a fixed unit (and being able to clean in between), I have heard of double glazed windows eventually trapping dust etc after a few years. With this I can remove them in summer if i wanted to

[Tinkerbell2]

Hey there. I am a kiwi too, and I have the worst condensation in the country (at least it feels like it...lol). If you actually sealed the perspex, do you think it would cut out all the condensation? Thanks. Hope you're enjoying 'God's Own'

[shanitan]

It really does cut down condensation on the glass but there is still some on the aluminium frame - to reduce that you'd have to extend the perspex to cover as much of the frame as possible. My guess is if your windows are like mine - ie 1 fixed and 1 opening, then extend the fixed frame piece. We cant do that now as we have cut all our perspex down to size....

[Tinkerbell2]

Thanks for that. Appreciate your time. Cheers.

[Broom]

Brilliant, easy, elegant, cheap*. Love this 'ible!

• (when compared to commercial window solutions!)

[shanitan]

yeah, the commercial ones which do really the same thing in principle (prob a bit more flash in construction and have handles to remove the plate) cost like at least 5X more for a single room. We wont try it on the patio doors yet till we are better at measuring ... haha

[omnibot]

Good one. Notice any savings on heat yet?

[shanitan]

dont know, this is our first winter inNZ (formerly tropical babies we were!!) just been in this house about a month only also. But there is less condensation on the glass (the exposed bits of aluminium frame still have condensation - so in thr revised version of this, we will cover the entire alu frame

[baustin]

This is an excellent instructable! So simple yet extremely valuable. Would like to see some prices on the acrylic you used and the magnetic strip. Thanks.

[shanitan]

Hi, The magnetic strips were from Mitre 10 mega (a popular DIY store in NZ) an cost about $15 a roll (cant remember off hand how long) and each window needed about a roll. The acrylic cost different for each window, but for the 2 seen in this picture, we paid about $100.