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Make a maintainable DIY double-glazed window

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Double-glazed windows are usually made from pre-fabricated glass panels.  Although this is a good design to reduce the cost and complexity of manufacture, there are drawbacks.  For example, if a double-glazed window is broken, replacing it may be very difficult and expensive due to custom sizes, discontinued models, and companies going out of business.  Most double-glazed windows are only expected to last 10 years in moderate climates, and less where there are temperature extremes due to the seasons, which is reason enough to be able to maintain a window.

The design shown below is a true DIY double-glazed window.  It can be built and maintained by a person of modest skill; and at minimal cost.  If someone breaks the glass, it can be replaced with readily available glass sheets from a home-supply store.  If it begins to collect moisture, the seals can be replaced and new desiccant can be added.

One often-mentioned disadvantage of an air-gap (instead of noble-gas filled) double-glazed window is the convective loss due to air circulating around in between the sheets of glass.  Other gases may lower the convective losses due to higher mass, which leads to slower diffusion.  However, I think that most older windows have long since lost whatever special gas filling they may have once had.  Air-filled windows have the advantage that a normal person can replace glass and replenish desiccant without any special equipment.

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You suggest trying not to paint over the screws, you could always paint the parts first.
whoofoto1 year ago
There are some comments worth reading by "TheWindowMan" in the UK at this link. http://www.thewindowman.co.uk/misty-wood.htm

Here are a few of his remarks:

"The biggest problems with wooden frames arises because (unlike PVC-U and Aluminium) the sealed units are not drained, and the perimeter of the sealed unit is not ventilated"

"Sorry if I seem to go on about double glazing sealed units not lasting in wood windows, but this is what I see in real life almost every other day!

"Sealed units fitted in wooden frames MUST in my opinion have near a quarter inch gap between the glass and the wood at the bottom of the frame AND slotted holes to allow both drainage and ventilation. If sealed units are fully bedded and puttied into wood frames (even with non setting butyl putty) this is what you can expect, usually showing signs of failure between 6 and 8 years at most from new."
76special2 years ago
"One often-mentioned disadvantage of an air-gap (instead of noble-gas filled) double-glazed window is the convective loss due to air circulating around in between the sheets of glass."
The primary factor in convective loss due to circulation is the thickness of the spacer. Noble (Argon etc..) gases are less conductive than air, but you'll still get circulation losses if you go over about 16mm (I think). As long as you keep the gap between the panes less than 16mm you should be fine.
Where I work we make double glazed fridge doors, and the widest spacer we use is 14mm, with or without Argon.
Looks good though. I'm looking at doing something similar and would really like to see a finished unit.
Once sorted you could design a custom router bit to cut the profile in a single pass.
neffk (author)  76special2 years ago
Oh. Well thanks for posting. I'm mainly going off the information I could find on the mighty interwebs, which I trust less than real experience.

You could certainly get a shaper bit that cuts the profile. I don't think it's terribly expensive. If you could spread the cost over enough windows, it'd probably work out really well.
thekatr22 years ago
Great job
owais403 years ago
Please explain to me the function of the "O-ring" and how can the desiccant be added to the window without looking odd as it can be seen from outside. Kindly also show the picture of the O-ring that you used. My email address is owais40@gmail.com
owais40, when you put the windows together make !!sure!! it is low humidity or you will get condensation in between. boatboy
neffk (author)  owais403 years ago
http://www.mcmaster.com/#o-ring-cord-stock/=bkfvyc

The o-ring keeps additional moisture from getting into the window. I don't have a picture of this because I haven't started building my custom windows yet and the one shown here was just a proof of concept.

The desiccant is added through a hole in the top of the frame. It must be plugged with something air tight. I did not use desiccant in the prototype, so you do not see the hole in my pictures.
owais40 neffk3 years ago
Thanks for your quick response.

How many O-rings will I've to put on one side of the window for one glass for best results. Also in my opinion the diameter of O-ring should be slightly more than the cross-sectional length of the groove, while keeping its height equal to the O-ring dia., for the O-ring to be able to seal the glass to the frame. Please tell me if I'm correct.
neffk (author)  owais403 years ago
You should probably just buy the cord stock. Otherwise, you'll have to account for axial stretch and, if you're making several windows, you may have to order several o-rings---and they usually come in multiples. They're already an expensive part of the project, so I doubt you'll want to have a bunch of extra inventory.

For a better seal, you could use a set of concentric seals... hadn't thought of that. Well, it will be more expensive, but it might be worth it.

If you match the areas, the o-ring will protrude above out of the groove. For a low-pressure application like this, it might not matter if the o-ring material bulges out of the groove when you tighten down the glass. Well, I suggest you use equal areas. If you do something else that works, let me know.

neffk (author) 3 years ago
Got a great suggestion to use knurled brass thumb screws with threaded inserts for parts that can be disassembled. Sounds like a really great idea. I can't wait to give it a try.

pmartinez3 years ago
One thing to say: Awesome !!! Is what I needed
neffk (author)  pmartinez3 years ago
If you make any windows, post a picture, so we can see your interpretation.
pmartinez neffk3 years ago
You bet. I hope not to let down the pros, but I'll try. cheers
Howard744 years ago
This is a good idea, and have been thinking about doing it for awhile.  I've been trying to install a solar air heater first before the winter hits here in Ohio.  Have you had any experience with these?
I think I found a really neat one at solarairsystems.com.  
neffk (author)  Howard744 years ago
For solar gain, you generally want single-glazed windows for maximum thermal gain.  Remember to use 1-way valves in the ducting to prevent cooling at night.  There are some great resources on the web that can help you calculate the amount of mass and window area you need.  My favorite is

http://www.builditsolar.com/Projects/SolarHomes/PasSolEnergyBk/PSEbook.htm


scavanger4 years ago
 This is really an interesting idea. Thanks for posting it.
I have been thinking about a similar project, but have not gotten any further than thinking about it yet.

My first thought when looking at this design is: I really like the o-ring idea. But I see a possible flaw in it. Without the use of glazing compound water will be able to get between the glass and the sash. Only a small area of it, but over time this could possibly be an issue.
neffk (author)  scavanger4 years ago
Good point.  Hadn't thought of that.  Maybe you could calk or glaze it after installing the outside trim.  As long as the putty is on the outside, it would be accessible and possible to remove.
scavanger neffk4 years ago
 Yes, I think glazing the exterior would be a good idea. 

I just had an other thought too. Instead of an o-ring I wonder if screen spline would work. (that grey or black rubber used around aluminum window screens)
It is available in a couple different diameters and is readily available at most hardware stores.

.200 screen spline on Amazon 500' for $20.61 Just under a quarter inch and enough to do a ton of windows.
neffk (author)  scavanger4 years ago
I think the main issues are the diameter and hardness.  You can choose dimensions of the groove to match the spline, so that's not a big deal.  But I've found that the spline material is rather hard, so it may be difficult to seal the window without cracking the glass.  I found that the corners are particularly sensitive... You'd have to tighten down the trim slowly and evenly around the whole frame---like a head gasket.  Also, remember that wood screws are only good for about 7 lb/thread, so the length of the screws may have to be longer to accommodate the harder seal.
kill-a-watt4 years ago
wait, you used silicon caulk instead of an o-ring? How big in diameter is this o-ring? Or are we talking about long round strings of rubber?

When I was sorting out how to do this in my head, I was thinking the way to do this would be to step the frame, and thus have one piece of glass maybe 1/4 inch bigger all around. I would have also used glazing points to hold the glass in place. I've never tried silicon instead of glazers putty, but I don't see why it would not work.

I'd probably give the frame two coats of "curb-shopped" exterior grade paint, especially if I was adding desiccant, before putting in the glass
neffk (author)  kill-a-watt4 years ago
Right.  Don't use calk if you ever want to get the glass out.  Being able to remove the screws and tip out a single sheet of glass is the most important feature of this design.  But my wife wanted to see that the air gap would work as promised, so ordering 10' of tubing would have only added un-necessarily expense. 

The O-ring cross section should have an area equal to the cross section of the groove.  Otherwise, it will bulge out and crack the glass or get pinched or cause the space shuttle to explode or something equally horrible.  You can buy tubing stock that isn't connected at the ends, and lay that in the groove.  Where the tubing ends butt together, a dab of calk would be needed to keep the inside of the window dry.

Glazing putty can be a bear to get off.  The old stuff was lime and linseed oil and maybe some clay.  But the new putty is something else that is sometimes a real chore to get off.  If you use putty, you'll have a hell of a time getting it out.  Remember, you can't just push on the other side of the glass---there's two layers.
mrmath4 years ago
I thought about doing something similar to this in older windows, but never got around to it.  Are you seeing/feeling any advantage?
neffk (author)  mrmath4 years ago
If you have oddly-sized windows, or have many fixed windows, the advantages are greater.  But this type of window retrofit may only be economical if you have more time than money and already have a table saw and a goodly selection of tools.  The part that's shown here is but a small fraction of the work involved.  If it's a retrofit, much more effort is required to ensure that windows will fit into the existing frames.  Various hardware and weatherstripping can take a lot of effort.  But for new construction of large non-moving windows, I think this would be a really good way to do it.
For new construction, I've seen plenty of high quality replacement windows that were special ordered but measured wrong. They turn up at the ReStore that's run by Habitat for Humanity.  As long as you can be flexible with the window size in the new construction, you can rough in whatever you have managed to scrounge up.

Something like this really shines when you have an old wooden window in good shape, but with a busted or rotten frame.
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