Make a Maintainable DIY Double-glazed Window





Introduction: 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

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

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

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

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).



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    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.


    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.

    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.

    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.

    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.

    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.

    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!

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

    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.


    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.