Introduction: Make a Maintainable DIY Double-glazed Window

Picture of Make a Maintainable DIY Double-glazed Window

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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Step 1: Making the Frame

Picture of Making the Frame

The sash of the window is the trick to this design.  It acts as the spacer between the sheets of glass; it  provides a place for the O-rings that seal the glass to the frame; it provides a place to add trim, which holds the glass in place; and it provides a structure that supports the glass.

The air gap is created by using the wood of the sash.  I used a 1/2-inch gap.  Note that the thermal performance of this window sash is improved by not using a metal spacer between the layers of glass.

I designed my frame to accommodate 1/8" glass and 3/8" trim.  The O-ring groove is 1/8", which is a poor choice because there were no available  O-rings with the appropriate diameter.  You should find the O-ring and let that determine the width of the groove.  The O-ring should be chosen based on it's cross-sectional area.  That area should match the cross-sectional area of the groove.  See the selection at  I was surprised at how much some of these materials cost.  Find something weather-resistant so the UV-radiation doesn't destroy it immediately.  For my prototype, I used silicon calk, which was cheap but will make the glass very difficult to remove.  DO NOT USE CALK!!

The wood that I used for this demonstration is pine from framing-grade 2"x4" lumber.  When I do this for a larger project, I will use something much nicer.  I've read a lot about windows and there doesn't seem to be a consensus on what wood is best for windows.  I would use white oak, but most any hard or soft wood can be found in commercial use, so I guess it doesn't much matter.

When you're cutting this profile, make sure that you produce enough for your project.  Measure the outside perimeter of the windows and add 10% to the total for all of the windows.  If you are making a frame for a very large window, or if your stock is short pieces, you may have to be more careful about the exact amount of stock.  Also, for a window larger than 3'x3', you'll want to make something more sturdy than the design presented here.  Just a thought, Mr. Fox.

One of you will want a drawing of the cross section---I just know it.  I've decided not to provide a technical drawing because the point of this article is to demonstrate a concept; it's not a engineering consultation.  You'll know the difference because concepts are free.  The other comes with a fee---and usually 10% up front.

Step 2: Assemble Frame

Picture of Assemble Frame

Assemble the sash.  This design requires that you miter the corners instead of some fancier joint.  (Some joints are, indeed, stronger than others.  But the point here is to get something done, not argue about obscure points of jointery.)  The groove for the O-ring must be continuous in order to make a good seal.  You could probably get away with some other joint, but you'll have to do some whittling to get a continuous groove.

Use wood screws (coarse thread, flat head) to hold the frame together.  These are counter bored because I had pan-head screws.  If you have flat-head screws, a counter sunk holes would be nicer.  Leave the corners a little loose until the glass is in.  The frame doesn't have much strength itself, and having it rigid will just make it harder to put glass into it.  The glass will probably have 2 factory edges, which should keep the whole works square.

Step 3: Cut Glass

Picture of Cut Glass

Cutting glass is not too difficult.  There are just a few important things to remember.  First, you should take normal precautions---wear gloves and try not to get anything in your eye.  Then, you need a work surface that is flat, clean, and really strong. Use a dab of light oil on the glass cutter before you start.  Third, use a straight edge and figure out how to clamp it down at the ends of the cut.  Cut using one motion, as smooth as possible.  You have to press hard---there is a sound that tells you when you're doing everything right.  Then grab the glass at the end and sorta twist it along the cut. 

For this window design, you'll need to measure accurately within 1/16" or so.  That sounds hard, but it is well within the ability of normal people.  I know, because even I can do it.

Find some YouTube videos if you want to know what cutting glass sounds looks and sounds like.  For example, right around 3:05.  Or, 

After you cut the glass, polish the raw edges before doing anything else.  You can use a file or 400-grit sand paper to take the sharp edge off.  The file will make little glass chips, so don't do this part over carpet.  The sand paper makes a little dust, but is altogether less messy than the file.

Step 4: Assemble Window

Picture of Assemble Window

Dry-Fit the glass in the sash.  Then, take it out, add seal (use O-ring, NOT calk), put the glass back in, and add the trim.  Then, paint it with outdoor paint, add hardware, and call it done. 

When you add the trim, tighten it down slowly.  Begin with the screws near the middle of the strip of trim and work your way out.  This avoids putting too much pressure on the corners of the window, which are quite fragile.  There is probably some way to relate torque to durometer of the seal, but you can just tighten based on your intuition.  If you have a lot of moisture problems, change the desiccant and tighten down the trim a bit more.

The whole point of this project is to have a window that can be fixed, if need be.  But fixing usually requires taking apart and that may be a problem if the screws have been painted over.  Also, most people won't like to see the screws that hold on the trim.  So, try to think of a way to cover the screw heads that allows for maintenance and looks good.  And you have to do it so that the next home owner realizes that there is a way to maintain the windows.  I haven't hit on the perfect solution yet.

Desiccant should probably be placed between the sheets of glass.  You could add a hole at the top of the sash for this, and seal it with a large screw or a conical dowel.  You can buy desiccant at McMaster-Carr.  You can also use dry air to fill the window if you have an air compressor.  I think some moisture will come from the wood, so it may be advisable to paint the wood bits before and after assembly.

After a year, the window pictured here has worked without fogging.  Granted, it was not in my kitchen or  bathroom, where humidity problems normally crop up.  The window is in my tuck-under garage, so the temperature extremes are less than could be.  But it was the only part of my house where I was able to avoid the oversight of the Decorating Committee, so it was a good place to experiment.  I did break one of the panes of glass and was able to replace it.  The calk is a real hassle.  I think the O-ring idea would work a lot better.  And if you're making your own windows, you're saving so much on the project that buying the o-ring material should be justified.

Step 5: Addendum

Inside Trim:

If you use standard-drive screws (not Phillips, square, hex, etc) you can usually chisel paint out of the groove.

A decorative knob can be used to cover screw holes.  Unlike flush plugs, the next person who works on your windows will have a clue about how to take the window apart.

Weather-Tight Seal:

Perhaps the outer pane should be held in by points and glazing.  That's the traditional method and it might be air tight.  Perhaps a a small bead of calk around the glass, after it is installed, would provide the seal.  The weather-resistance would be provided by the window putty, which could be applied after the calk dried.

Sometimes it can be really hard to get newer window putty off.  Traditional putty, I think, is easier to work with.

If you use putty, seal the wood wherever the putty touches with boiled linseed oil and leave it un-primed.  Paint over the glazing a few days later, overlapping the glass 1/16 inch or so (several millimeters).


mkcf (author)2017-11-07

Let me preface this by noting that I'm a professional millworker by trade, and I make windows all the time. I'd like to note a couple things. First, traditionally constructed window sash can be done without expensive machinery- you can do it all by hand and get better joints than many modern windows have. If you want to use a tablesaw and a router those can certainly speed you up, the main work being in sizing the timbers and making sure they are straight and square. The mortise and tenon joints are not that hard to cut with saw and chisel. Second, air sealing the stops, parting bead, etc. with pile and bulb weatherstripping where applicable will get you much farther in terms of energy conservation than adding double glazing. Wall cavity insulation is another topic we'll have to address later, but I'd like to also note that if you have single pane windows and no insulation in the wall cavity, I'd start there rather than try and retrofit or make new windows.

So why DIY double glazing?

The certain eventual failure of commercial double glazed (IG) units makes them undesirable, also the very ugly wide sight lines. In many cases it may be desirable to sacrifice some insulating value in the interest of maintaining the beauty of old wood windows- this can be done by restoring them to their original condition and adding storm windows, however storm windows have their own issues. Very cumbersome if installed on the outside of the building, the permanent aluminum ones don't do much in terms of insulation although they do address the need for window screens in summer. French doors in particular is a really good place to use glazing as storm doors are problematic in terms of ease of entry as well as potentially collecting moisture towards the interior- I've seen it happen.

Therefore I'm writing because I'm curious how MtnM's windows were done, more detail please, and how have they performed, no condensation in between the panes for 10 years you say...? What material did you use as a spacer? Did you use putty to hold the glazing or wood stops, or some other material?

My guess is that your windows had a single lite rather than muntins dividing the window (as you mention holes drilled in the jamb side of the sash)? One would have to devise a way for moisture to egress in that situation. Any ideas on this?

An interesting bit of history is that the original Thermopane window glazing was made by welding two panes of glass together by melting glass around the perimeter, sealing them together. No rubber or other junk in there, just a hollow pane of glass essentially. Sadly this technology was abandoned as it was discovered that wider gaps between the panes results in better insulation and they don't make 'em anymore. I'm looking into the method as it strikes me as a perfect solution. If I find a useful answer I'll follow up my post. Cheers.

MtnM (author)2017-10-21

I did make my own double glazed for my home using a method similar.

1) To prevent moisture I drilled holes into the spacer area. The holes come from the side which will slides. It has worked well over the past 10 years. I did not use a desiccant, and am happy I left it out.

2) Smaller spacer dimensions limit convection. I used around 3/8".

3) I did not try to add any O-rings. Seems to have worked out well.

4) I used redwood after a great deal of thought. It has held up well. I did make a mortar and tenon joints, which has held up to the motion of opening and closing. The supposed con of redwood is it will not hold a glued joint, but it has worked for me. If price was no object I would love to have used quarter sawn white oak but could never find enough for the project in a quality and price which made any sense.

5) I did use clear silicon caulk to seal the window glass. It worked well. Better than traditional glass putty. On other windows I've used both putty and silicon; if anything replacing glass which was silicon sealed was easier than the putty/triangle system.

6) The store was more than happy to cut all my glass for no additional charge. It was great as they had all the correct set-up, safety gear, and kept the glass mess.

It really made a great difference to my house. I normally have winter weather reaching -40.

soupdragon32 (author)2017-01-02

Hi. We aquired some 8 x 4 (feet) single glazed panels, 3 of which we have used in a 'sun room' extension. We have enough panels to create 'double glazing', but are wondering what would be the best wsy to go about it, bearing in mind that the existing panels are already fixed in place in timber frames. They are recessed within the frames, so there is room to add an extra panel.

adamtimm1 (author)2016-12-19

Actually it does matter what wood you use because the more porous woods absorb moisture more easily. That means in a sub tropical climate the windows could expand and contract with changes in humidity. It is only logical that denser less porous woods will better maintain their dimensions. Also the harder woods are, at least to me, easier to work.

OolongJ (author)2016-10-19

Silicone caulk could be used as a seal by running a bead along the groove, waiting for it to dry, then adding the window.

Cheaper and softer than an O-ring. If squeezed with equal pressure and layed at even speed it should work very well.

rjhawes (author)2016-01-24

After learning a whole lot about windows, prices, insulation, etc, I am saying NO to commercial windows and making my own. This instructable has been very helpful in getting me started. Thank You!

I'd like to add a not about cutting glass. I've been a glass-maker and glass educator for about 15 years. I'd like to suggest that DIYers read the glass-cutting portion of this instructable with a grain of salt. Some of the writer's suggestions about how to cut glass are inaccurate. Here are my suggestions for glass cutting.

Gather the following: safety glasses, gloves, a piece of carpet, cutting oil, glass cutter with oil reservoir, running pliers, abrasive material and your phone.

Also search for and watch videos on the following: how to carry sheets of glass safely & how to cut glass safely. Most videos will focus on stained glass (ie: small pieces of glass), so make a point of finding videos that address larger sheets of glass such as what you'll be working with in making windows.

Safety Glasses: most important piece safety equipment. Why? Because it's easy to damage eyes for life when a piece of glass flies up there, especially if you react like a normal person and try to rub the irritant out of your eye. When you break a piece of glass along a scored line, the top surface of the glass breaks into teeny tiny pieces and flies away from the break. If you're snapping glass properly, that means up and away, towards your body. Most of those little pieces never get close to you, but once in awhile... If you don't believe me, do a search for videos of sheet glass breaking in slow-mo.

Gloves: and long sleeves, long pants and closed-toe shoes. If you're working with window-sized pieces of glass, that's enough glass to cause serious injury or death if it slips, falls, etc. A layer of material between your skin and the glass is helpful, especially if it's denim, leather, or other material that provides resistance to glass cutting through it. Glass is potentially deadly if you happen to get cut in the wrong place and with enough depth. Respect that.

Carpet: find a piece of low-pile carpet that is larger than the largest piece of glass you're going to cut, nail it to your work table. Use that to cut all your glass, vacuum it once in awhile if it get full of bits of glass. Even though it seems counter-intuitive to use carpet (what? it'll get full of bits of glass and scratch my windows!), it's better than a hard surface. Glass is fairly brittle and if you're scoring with your glass cutter on a hard surface, and there are any variations in surface (dried glue, solder, nail-head), your glass will break from the uneven exertion of sufficient pressure on the surface. It might break where you're scoring, or it might break where there's a nail head poking out 1/32" from the table. The carpet buffers uneven pressure on the glass. Sometimes people use homasote, a spongey wood/paper fibre board product. Vacuum up little bits of glass regularly, use a low-pile carpet (like carpet for commercial / high traffic areas) and don't run your hand over it looking to see if there are little bits of glass in it.

Cutting oil: Glass cutter sellers and manufacturers will says you need to use their oil, but that's not true. Any oil that is of low-viscocity (thin & runny), will work, and glass cutters with an oil reservoir usually come with some oil. I use sewing machine oil. It's the right viscosity, is designed to wash out easily and I happen to have an industrial sewing machine that uses the stuff. If you don't use oil, all the tiny bits of glass you're creating when you score glass will become embedded in your cutter and render it useless. Those little bits of glass also act as abrasives against your glass cutter, dulling it to the point of uselessness after the first several cuts. Do be sure that you wash the cutting oil off your glass once you're done all cutting. You may not notice the oil right away, but once your finger prints and the oil start to yellow on your otherwise lovely windows, you'll be sure to curse your inattentiveness to detail.

Glass cutter with oil reservoir and diamond: Cheap cutters from the hardware store are a few dollars, let's say $5. They'll last several cuts and are made of hardened steel. A decent cutter with oil reservoir and diamond head will last the rest of your life and cost anywhere from $10-$50. Find one online, or visit your local stained glass supplier, compare prices, the value of your time, etc and go for it.

I store my glass cutters with oil in the reservoir and in a little glass jar with oil in it. I also use a chamois or piece of leather that I run the cutter over every once in awhile if I'm doing a lot of cutting, to remove little bits of glass from the wheel. Most cutters have a round wheel-head, that has 1-5 diamond-heads on it. When one head dulls, you rotate the wheel so the next, brand new diamond head is ready for use.

Running pliers: They aren't absolutely necessary, but they do make it easier to assert even pressure on both sides of the glass when you're snapping one piece in two. Running pliers also keep your hands that much further away from potential injury. When new to glass cutting, it's a weird feeling and it takes some practice to understand how the glass will break and how best to keep safe. When you watch videos on how to cut glass, most will show the use of running pliers, but you'll also probably see people doing it with their hands. Both are good. Sometimes, with larger sheets of glass, running pliers are nice because they make it easier to exert even pressure on both sides of your score line. You don't need thick glass for windows, but if you want to use thicker than 1/4" glass because it's sandblasted, or you happen to have some, then the average running pliers won't fit, and you'll need to find yourself some beefier running pliers. They'll be described as being suitable for sheet glass that is 3/16" or thicker.

Abrasive materials: Sand paper is 'OK', but not not great, and here's why. Glass that has just been scored is sharp, and I mean really, dangerously sharp. If you slide your hand along a newly cut edge, you will cut yourself. Black/wet/dry Silicon carbide sand paper is great for sanding glass, but maybe not for the edges of just-cut glass. If you sand with the edge of the glass, and if you cut through the sand paper... you'll have a bad cut on your hand. If you use sand paper against the sharp edge of a sheet of glass, much of the abrasive grit will break off of the sand paper backing before doing anything to the glass. I suggest a grinding stone, diamond pad or a rock. Yep, a rock will work well, especially if it's granite. Granite is a fun thing to show off, but a grinding stone of any shape or a diamond pad are probably the most effective. Harbor Freight tools (in the USA) has them cheap. Grind along the sharp edges of the glass. You don't have to do much, but you should. 30 seconds per side of sheet glass could make the difference between 'whatever' & 911.

Your Phone: Or a person within hearing distance. Sheet glass is great, but a major cut can kill you, and it can happen in the blink of an eye. If you're new to cutting lots of sheet glass, learn how to do it safely and don't let your attention stray.

Thanks for the instructable. This is a great primer on making my own windows.

Lokislash (author)rjhawes2016-07-04

You rock for this post! I actually work at a glass shop where our specialty is insulated glass units. I can't think of a day where at least one of us hasn't said "Glass is sharp!" I found it a little annoying at first, I was wondering if everyone thought i was stupid, but then I realized everyone said it to everyone else. And when you're around glass all the time, you can let your guard down. I'd much rather be reminded by a co-worker, than a giant glass shard. And bad stuff can happen in the blink of an eye!
"Glass is potentially deadly if you happen to get cut in the wrong place and with enough depth. Respect that."- omg, I LOVE how you said that!

MuranoBlue (author)rjhawes2016-06-11

This could be an instructable on its own. I've cut glass before but never heard of sanding the edges.

JoeH77 (author)2016-01-06

Did you fill with Argon, or pull a vacuum on the void? If not how have you prevented condensation on the inside of the void?

I like this idea, I thought I would make just the Spacers, assemble them, then use Automotive window tar, (comes in flat tape form) throw in some Desiccant, then seal it up. I will try this this winter while it's dry down here in South Louisiana, and hope they dont sweat this summer. These are for the Shop, so looks are not that importaint.


neffk (author)JoeH772016-01-07

No argon. That was too high-tech for me, at the time. The air gap is optimized for dry air. Somewhere in the article I think I suggested desiccant but I didn't have a chance to try it out. That windows is in a house I sold, in a partially heated garage. It worked fine for that. But the real test of a double-glazed window is when the temperature difference is large, so don't take my experience too far.

WilliamG60 (author)2015-11-24

This is just what I'm looking for, it all looks reasonably easy and rather than use the window as my main I'd be looking to use it as secondary double glazing and leave my lovely bay sash window in place at it is.

There's only one part that I would find difficult and that's sourcing/making the window profile. Did you get that off a shelf, if so what do I need to look for? Otherwise I presume you've used a router, if so is this easy and what bits would one need and can a good result be achieved with a simple plunge router.

Many thanks in anticipation.



neffk (author)WilliamG602015-11-24

The profile is the most difficult part of this project. I cut my own with a table saw. Professional windows are made, I understand, with shapers, which cut out the profile in a single pass with a custom blade. I don't have that kind of equipment so had to cut it out bit by bit.

atukwase (author)2015-10-19

hey i would like you to send me the steps of constructing a wooden window. thx

I think he only works with glass windows :P

ali25 (author)2015-07-25

Hya. I need to replace the glass in front door ( double glazed) & have been told v difficult with beading etc could you advice me? Thanks

neffk (author)ali252015-07-27

Sorry, I don't know you well enough to give good advice. To DIY or not is a philosophical question. I default to DIY and re-consider based on danger, cost, and availability of free time.

LemoniaK (author)2015-06-18

Hello,I have a question I would like to attach a plastic panel for shading to a timber window frame, the panel is about 12 kg. Is there any adhesive that I could use to glue the panel to the frame? If not, could I screw somehow the window frame, without create a thermal bridge? Thank you!

neffk (author)LemoniaK2015-06-18

With good preparation and the right adhesive, you can do it without fasteners. Of course, if you do everything right, it's fairly permanent. If you use shorter screws, they won't be a very good thermal bridge. I've heard 7-lbf per thread so you can get away with fairly short screws. If you want some redundancy, use 8 instead of 4.

LemoniaK (author)neffk2015-06-18

Thank you for you answer! I was also thinking an adhesive, but do you have any idea of a product-adhesive that could perform well for two different materials, wood(porous) with plastic?

LemoniaK (author)2015-06-18

benjamin.namssorc (author)2015-04-29

A word of advice- spending a bit more on your glass cutter will make a hell of a difference. Good glass cutters will have a reservoir for the oil and work far better. Never make more than one pass with the tool, it will end in disaster. If you do it properly, with a good cutter, you won't need much force to either score or snap the glass.

neffk (author)benjamin.namssorc2015-04-30

Since I wrote this, I've used a quality diamond-tipped cutter. It's amazing. If you use the hardware-store cutter, you need a lot of pressure and a good jig. The one I used here is not very easy to use.

The thing about cutting 2x... If your cutter isn't making the right sound, you're not pressing hard enough and you can usually cut again. I've sometimes had a successful second cut in really thick glass but it's a last-ditch work-around type move, at best.

jdwoodschild (author)2015-03-30

I have a crazy, cooky question.

I want to make a permanent greenhouse, attached to a shed sized building. I was thinking about doing 16 inch center framing, solid and insulated bottom 2 1/2 feet, then windowed up to the roof line, and making the windows fit inside the framing, instead of building the framing to the size of the windows.

One, would something like your design concept work for my idea, and two can I do this with clear acrylic sheeting instead of glass?

Thank you so much!

neffk (author)jdwoodschild2015-03-31

Sure. Do look up the angle of the sun and get the orientation right before you start building.

The issue with windows on 16-in framing is that 2x4s cast a giant shadow when the sun isn't straight on. This highlights one of the major problems with passive solar design---if you aren't careful, you can easily take up 10-20% of the area with framing. The other problem is that 16" centers is a code designed for 5/8" plaster board and has to do with sagging between supports. Structurally, you can get away with a lot less wood, even up here where we have 50 lb/sqft snow load requirements. Taken together, these issues argue for wider windows and metal framing for maximum effect. Still, we're all constrained by our own budgets and available material.

jdwoodschild (author)neffk2015-03-31

Hehehe you are either going to laugh at me or call me crazy, but this is an idea for my THOWs I'm designing (Tiny house on wheels for the uninitiated). I want to have the last 6-8 feet of my tiny house to be a green house with acrylic windows and the clear ish roof panels. I like the idea of fixable Windows, and building it myself so ican have it to my specs.

Am I totally crazy for thinking this will work?

neffk (author)jdwoodschild2015-04-01

I think it's a good idea. Read through the other comments while you're thinking about making windows water tight. There's details about how to paint to seal the glass into the frame, etc.

Do us all a favor and make an instructable when you get around to making the windows. I'd really like to see what you dream up for 2.0!

neffk (author)jdwoodschild2015-03-31

Yes, you can absolutely use acrylic. (To be as obnoxious as possible, call it polymethylmethacrylate....poly-methyl-methac-ryl-ate. Has a nice ring to it, doesn't it?)

guy.pepin.509 (author)2015-02-17

Thank you for this fantastic instructable. May I suggest that some woods are better than others in two respects: dimensional stability, and rot resistance. SPF (Spruce Pine Fir) is a decent wood with reasonably long lasting qualities. However, I believe the wood of choice would be Tamarack or Larch, which has both qualities in spades. Regrettably it is not generally available as dimensioned lumber so you may have to look around for a source, and a sawmill to cut it for you.

tylerwhitworth (author)2013-08-28

You suggest trying not to paint over the screws, you could always paint the parts first.

whoofoto (author)2012-09-29

There are some comments worth reading by "TheWindowMan" in the UK at this link.

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."

76special (author)2011-07-17

"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)76special2011-07-18

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.

thekatr2 (author)2011-06-18

Great job

owais40 (author)2011-03-23

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

boatboy1 (author)owais402011-03-29

owais40, when you put the windows together make !!sure!! it is low humidity or you will get condensation in between. boatboy

neffk (author)owais402011-03-23

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 (author)neffk2011-03-24

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)owais402011-03-24

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)2011-01-09

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.

pmartinez (author)2010-07-03

One thing to say: Awesome !!! Is what I needed

neffk (author)pmartinez2010-07-03

If you make any windows, post a picture, so we can see your interpretation.

pmartinez (author)neffk2010-07-04

You bet. I hope not to let down the pros, but I'll try. cheers

Howard74 (author)2009-12-01

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  

neffk (author)Howard742009-12-01

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

scavanger (author)2009-12-01

 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)scavanger2009-12-01

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 (author)neffk2009-12-01

 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)scavanger2009-12-01

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-watt (author)2009-11-27

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-watt2009-11-27

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.

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