# Forum Home Renovation Doors, Windows, Architraves & Skirts  Double-glazing fixed panes

## Compleat Amateu

I have 4 fixed windows (ie non-opening). Timber framed in brick veneer, 70s yellow patterned glass, top edge parallel to cathedral ceiling line, ie not rectangular. Verrrry 70s! In addition, 2 are cracked. 
I want to replace the glass, and double-glaze these. 
Ignoring the complexity of the irregular shape, is double glazing as simple as:
a) Knock out the existing glass
b) Insert a new sheet of glass cut by the friendly local glass people
c) Add a timber bead (10mm gap?)
d) Add another sheet of glass with a final bead to hold it in place? Of course, silicone each in place etc. 
And should I give any consideration to thermal properties, eg S-glass in one or the other sheet? If so, which one, the inner or outer? I assume the outer would be cloudy glass, since the windows are exposed to SE and NW light so cop a bit in summer. 
Is there anything else to think about? I had briefly considered getting new windows made to suit, but the price doesn't look pretty. 
Regards and thanks 
Compleat

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## bugsy

> I have 4 fixed windows (ie non-opening). Timber framed in brick veneer, 70s yellow patterned glass, top edge parallel to cathedral ceiling line, ie not rectangular. Verrrry 70s! In addition, 2 are cracked. 
> I want to replace the glass, and double-glaze these. 
> Ignoring the complexity of the irregular shape, is double glazing as simple as:
> a) Knock out the existing glass
> b) Insert a new sheet of glass cut by the friendly local glass people
> c) Add a timber bead (10mm gap?)
> d) Add another sheet of glass with a final bead to hold it in place? Of course, silicone each in place etc. 
> And should I give any consideration to thermal properties, eg S-glass in one or the other sheet? If so, which one, the inner or outer? I assume the outer would be cloudy glass, since the windows are exposed to SE and NW light so cop a bit in summer. 
> Is there anything else to think about? I had briefly considered getting new windows made to suit, but the price doesn't look pretty. 
> ...

  i dont think it is that simple
I had  double glazed windows made up .
dont you need to get all the air out or some gas put it between the panels?

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## pawnhead

They fill the void with freon, but even with just air in there, it would be a vastly better insulator than a single pain. However, with moisture in the air, there's a risk of condensation, and there's no way to clean the glass in the void if it's all sealed up. Pick a very dry day with low humidity to seal the second pane, and you should be right.  :2thumbsup:  There's no guarantees though, and I'm not a glazier, so I'd ask an expert before I committed to anything.

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## Bloss

> They fill the void with freon, but even with just air in there, it would be a vastly better insulator than a single pain. However, with moisture in the air, there's a risk of condensation, and there's no way to clean the glass in the void if it's all sealed up. Pick a very dry day with low humidity to seal the second pane, and you should be right.  There's no guarantees though, and I'm not a glazier, so I'd ask an expert before I committed to anything.

  Ah no - not freon now or ever - it was a refrigerant gas banned for a number of year now. And as Bugsy says - it isn't that simple. Some are simply evacuated (partially) and many use an inert gas, commonly Argon (same family as Krypton and Xenon as is used in halogen lamps, but Argon is cheaper). Most also have dessicants such as silica gel packs to absorb the last bit of moisture. Of course neither is possible for DIYers - the double glazing is made up in special factories as hermetically sealed units. Using plain air gap would work so long as the gap was right and you could dehumidify it, but not really practical. Some of the films help a little and there are after market plastic ones that also work a little, but not well.

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## pawnhead

Well there you go. Shows how much I know about double glazing.  :Doh:

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## Master Splinter

If you want to DIY the double glazing, here's a few ideas to kick around... 
Desiccant - silica gel is easily available in bulk - most pet stores stock the fancy long life odour absorbing kitty litter (it looks like rough white crystals, with the occasional blue one).  It's silica gel!  Put it in a square aluminium section with some small holes drilled in it and there's your desiccator unit. 
If you use 10mm square tube, you can run it around all sides as both a spacer and desiccant holder.  Secure glass to each side with silicone, and there's your sealed, double glazed unit. (air proof sealing at corners is left as a fun exercise for the reader). 
If you want to go fancy, have two (sealable) holes in one side.  Position unit upright so that both holes are at the top.  Borrow next door's mig welder and squirt nice, dry Argoshield (80% argon) into one of the holes.  It's over twice the weight of air, so it will displace the natural air inside the unit.  Add argon until the blow-out from the other hole tends to snuff out a match, seal the holes, and there's your argon filled glazing unit!

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## Compleat Amateu

Thanks guys, I'm well impressed with the sensibility (?) of these replies ... as I feared, it isn't quite that simple. 
On the other hand, pick a cold, windy and dry day (such as today is in Sydney), and some silica gel .... it's gotta be worth a go! 
The argon gig sounds way past my level of competence, could be a good idea if thought through carefully. 
Do we think silica gel wears out (i.e. saturates)?  Where do you buy it?

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## pawnhead

> Borrow next door's mig welder and squirt nice, dry Argoshield (80% argon) into one of the holes.  It's over twice the weight of air, so it will displace the natural air inside the unit.

  That reminds me of this video of an aluminium 'boat', floating in a tank of sulphur hexafluoride gas; 
 [ame=http://www.youtube.com/watch?v=1PJTq2xQiQ0]Ship floating on nothing![/ame]

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## sundancewfs

yes doing it yourself does work. Yes you will get fogging in between the panes. No it isnt the best way. Yes glazing silicon is the easy way. Yes it can be messy. Yes I have done it. 
I would only suggest this as a temporary measure until you can fit custom made double glazed units.(this is why I have done it) It is possible to have double glzed units made that are just the glass. These then fit into the existing frame you have.

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## autogenous

Depending on the unit type I think sometimes Argon is used on the units as a non-fog agent. 
Probably a little different to Australian styles of window but have a look just for ideas in regards to double glazing.  http://www.eurocell.co.uk/energy-efficient-windows.html  http://www.eurocell.co.uk/windows.html 
Another option is "comfort glass".  http://www.lexicon.net/~lis01101/Per...Ourhouse2.html  http://www.velux.com.au/products/acc.../comfortGlass/

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## Master Splinter

Love the video Pawnhead!!  
And as for silica gel...just about every pet store has the 'delux' kitty litter - even the Reject Shop has it (was about $5 for a 2.5 kilo bag, dump into smaller porous bags and add to your toolbox as an anti rust solution - at least that's what I did!). 
It looks a lot like this:  http://www.tidycats.com/Products/Crystals/ http://www.productreview.com.au/show...?item_id=63251 http://www.pookinuk.com.au/product-s...?productID=331 
Silica gel will store about its own weight in water...so unless you are thinking of filling the windows with water prior to sealing, a few good tablespoons worth should keep a window happy. (40 grams per three cubic feet is what some places quote) 
It does saturate (the blue beads turn pink when saturated) however, if the air is dry and there is no source of new moisture laden air, there's going to be no fresh moisture for it to suck up.  (hence the need to seal the unit well) 
As its a silica compound, it's pretty safe and nonreactive - but it will react to hydrogen fluoride, fluorine, oxygen difluoride and my old favorite, chlorine trifluoride...so you can't substitute chlorine trifluride for argon (or at least, not if you expect to keep living).

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## Compleat Amateu

jeez MS, we are off the topic now, but interesting nonetheless.  You aren't an industrial chemist are you?  Or maybe a country kid who got their kicks from ammonium nitrate, diesel and car batteries - now THAT I know about!

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## Master Splinter

...my favorite primary school library book was "The Golden Book of Chemistry Experiments" - I must have borrowed it at least a dozen times...I didn't have ammonium nitrate, but I did have nitrogen triiodide/amonium triiodide which was always good for a laugh (even if the iodine stains didn't come out).

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## Gravy258

Speaking from Experience, what you wanted to do originally will work! 
I've seen in Russia and Eastern Turkey secondary glazed windows. Normal outside window, same again on the inside. Usually with a nice big gap between the two. Very Effective. 
I've also put secondary glazing film over all my windows here in Melbourne. (non opening)
As I've mentioned previosly this is Gazebo grade clear PVC that comes on a roll. Stuck in place on the wooden reveal with fly screen framing. Framing being glued to window frames then plastic installed like mesh. This creates a 100% air tight seal and the wooden frame is the thermal break.  
I work as a fridge mechanic and have access to Dry Nitrogen so I could purge out all the air with Nitrogen and it absorbs moisture, but it hasn't been necessary. 
I did the first window two years ago. Before: metal framed windows sopping wet in winter and rotting Paint.
Now: No moisture whatsover on window frames, moisture forms on plastic skin instead.  
I don't tell visitors to the house about it, can't even see its there behind the nets. 
I usually do the double glazing in summer when its all bone dry, as the frames had to be repainted too. 
Very effective and has stopped the metal framed windows funghi problem and the usual benefits of double glazing. 
The missus dry's the washing inside during winter and it creates a lot of condensation, and its been no dramas 
Gravy

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## pawnhead

Interesting post there Gravy. 
I don't think you'd have to have a properly engineered, hi-tech system to reap most of the benefits. I reckon that simply a couple of layers of glass, with a 10mm air gap between would give you close to the same insulation properties for a fraction of the cost if you did it yourself.
I'm considering doing it myself. A drain-hole (probably unnecessary) and some desiccant.

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## Compleat Amateu

That sounds MUCH more possible, even reasonable.  Amazing how a post that agrees with one's needs is a powerful incentive to push ahead! 
Now .... how to get a 2500 x 700, pointed-top piece of glass into a window frame 4000 off the ground at its bottom edge?  And the ground is much less than horizontal ....

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## Master Splinter

The drain hole would provide a path for moisture to get in...either ventilate it (which beats the idea of double glazing) or seal it and use desiccant to scavenge out any remaining water vapour.

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## Goodintentions

I've been contemplating DIY retrofit double glazing for a while as a "green" energy/$ saving project & having now just bought/moved into my new/old house, it's creeping up the priority list.  Most peolpe I mention the idea to just stare blankly at me, so it was great to read through this thread of like minds.
I hope you guys don't mind me chiming in with my 2 cents worth?
Argon as mentioned peviously is the most commonly used air replacement in the vacum between panes in commercially produced DG windows mostly because of it's insulating properties (as far as I can research) & it's relative cost effectiveness in this role.
A vacum isn't absolutely necessary (as mentioned prev) it just maximises the insulating performance of the pane.
You can get a vacum pump & purge the air in the sealed space yourself if you want, which will help, short of trying to fill it with gas, which sounds difficult.  Ebay for vac pumps?  (www.GreenPowerScience.com then "vacum tube solar water heater" will find you a demo video of a vacum sealing project if you want some ideas.  Interesting site.)
Sealing the pane well & the desicant to absorb moisture is the most important to my understanding, but I too am no glazier.
Just using regular window glass without a vacum may well only be 1/2 as efficient as the full monty, but if that's twice as efficient (or more) than a single pane & you source your glass cheaply, at a clearance sale for example & DIY with minimal cost... then surely you can only win!
NB: I think that without a UV film or UV low E glass heat ingress is not hugely impeded by a double glazed pane, but heat egress  is improved substancially?  Is that right?

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## myla

hi, 
anything will help, both for heating and cooling 
seriously look at secondary window/glazing to get  a massive air gap 
i have single pane, 90mm air space then a double glaze unit the results have been fantastic 
thanks

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## woodbe

Also worth considering Low-e glass in you home made double glazing. You have 4 faces to play with on a double glazed unit. 
woodbe.

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## gray71

> I've been contemplating DIY retrofit double glazing for a while as a "green" energy/$ saving project & having now just bought/moved into my new/old house, it's creeping up the priority list.  Most peolpe I mention the idea to just stare blankly at me, so it was great to read through this thread of like minds.
> I hope you guys don't mind me chiming in with my 2 cents worth?
> Argon as mentioned peviously is the most commonly used air replacement in the vacum between panes in commercially produced DG windows mostly because of it's insulating properties (as far as I can research) & it's relative cost effectiveness in this role.
> A vacum isn't absolutely necessary (as mentioned prev) it just maximises the insulating performance of the pane.
> You can get a vacum pump & purge the air in the sealed space yourself if you want, which will help, short of trying to fill it with gas, which sounds difficult.  Ebay for vac pumps?  (www.GreenPowerScience.com then "vacum tube solar water heater" will find you a demo video of a vacum sealing project if you want some ideas.  Interesting site.)
> Sealing the pane well & the desicant to absorb moisture is the most important to my understanding, but I too am no glazier.
> Just using regular window glass without a vacum may well only be 1/2 as efficient as the full monty, but if that's twice as efficient (or more) than a single pane & you source your glass cheaply, at a clearance sale for example & DIY with minimal cost... then surely you can only win!
> NB: I think that without a UV film or UV low E glass heat ingress is not hugely impeded by a double glazed pane, but heat egress  is improved substancially?  Is that right?

  I would be sure the window if it is large will pull in or bend in under the vacuum unless it is really thick. I reckon old 3mm glass would flex to much, what do you think?

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## gray71

Just found this! RetroGlaze :: Double Glazing Specialists, Double Glazed Windows, Existing Doors, Victoria, VIC, Melbourne, New South Wales, NSW, Sydney, ACT, Canberra, Western Australia, WA, Perth, Tasmania, TAS, Hobart, South Australia, SA, Adelaide
Looks like what we are after.

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## Goodintentions

gray71 re: your question about the vacum pump flexing/distorting the glass.
This is possibly a valid question & I'm guessing in my answer, I think it would certainly depend on the thickness of the glass & the dimensions of the pane.  I think you are right in that 3mm glass becomes quite flexible once you reach a certain size.  
Is 3mm standard window glazing thickness?  
I think the crucial element would be the amount of vacum pressure required.  I don't imagine that one needs to apply a massive vacum force to extract the oxygen from the space between glass panes, but a good seal within the frame would be crucial to stop leakage after you close the extraction point.  
How to remove the pump connection & seal the hole without some kind of valve that remains in in the window frame to stop air rushing back in to fill the vacum ... I'm not sure how you work this bit out?
Trial & error. innovation & experimentation I guess?
I have to admit mate,  that for my part, this is all conjecture on an idea pieced together from different sources & as I've mentioned in earlier posts in this thread, I am certainly no glazier.
My interest in the whole concept of DIY retro fit DG was piqued when people I mentioned it to told me it couldn't be done or it was a waste of time.  
I'll certainly post any results when I get around to giving it a go.
Good luck if you gonna try it?

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## Goodintentions

Yep, there you go!  
It's obviously been on the mind of someone with wherewithall to work out a system to service the retrofit market/demand we are part of.
I knew it was possible & not a fools errand!
That system looks great from what I can see at the site from your link.  I'm yet to see if it can be applied to sash windows?  The old twist style window locks may be a problem, possibly need to be replced with something else to provide room for the additional pane?
The whole vacum idea may not be necessary at all, relative to the difficulty/cost vs any actual thermal benefit?  I do tend to get carried away with an idea.
I'm not far from Fairfield so I might head down & check out their outfit & will definitly get in touch with them.
Good work!  :brava:

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## gray71

Hey you never know unless you have tried! And unless others have tried or can disprove then anything is possible. I work in Kew and will pop in soon to see what can be done with our single glazed timber awning windows. Im pretty sure the glass they used to use was 3mm think. Ours looks pretty cheap as it distorts thing when you look through.

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## rrobor

Believe it or not, but glass flows all the time.  Try cutting old glass and its brittle due to this.  A very old window will be slightly thicker at the bottom than the top.  Odd but true.   Now if you create a vacuum between two sheets it may be fine for days, months or years but one day it will implode and chards of glass are going to fly. One Christmas we were having the gang for dinner. Wife needed a big bowl for chips or something and didnt have one. Nipped into Crazy Clints and got this large glass bowl. That thing blew up that night, Sitting empty all washed and ready on the table it shattered in several pieces. That is what tension in glass does, so dont make a time bomb.

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## Eastwing

Moen Glass - An Australian Glass Group Company

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## gray71

Ouch that could have been bad if anyone was near it when it blewup.
That website has some great info thanks for posting.

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## Master Splinter

Glass doesn't flow (at least not at commonly found temperatures), its yet another urban legend...  Does Glass Flow

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## rrobor

Ah well I was taught that.  So if that is correct why does glass become more brittle with age, and that I do know as fact cos Ive cut a lot of very old glass and even glass a few years old is tougher to cut

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## Master Splinter

The structure of glass may look smooth and uniform from our viewpoint, but in reality its covered in microcracks, irregularities and defects. (think of how concrete ages - from a nice smooth slab to chipped, worn and cracked). 
Tensile stresses build at these defect sites (localised stress concentrations) so the strength of old glass relates directly to the size and age of the sheet - the larger and older the sheet, the greater the probability of a critical defect being triggered by an additional stressing event such as glass cutting. (with glass cutting, you are applying enough energy to deliberately break the molecular bonds, so there is plenty of energy being put into the crystalline structure...if some of this energy hits a spot that is already relatively highly stressed - bang! - catastrophic failure!)

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