Replace single pane glass with insulated panes?

Stan in Oly, WA

Well-known Member
Except for the front rooms, most of my house has double hung wooden sash windows. Has anyone ever heard of replacing the single thickness glass panes with insulated double glass units (often called "thermopanes" after the brand name)? It seems to me that the sashes could easily be rabbeted deeper to accommodate the thicker insulated units, and they could either be held in place with points and glazing putty or stopped in with wooden trim pieces. The main problem I can see is that the increased weight would be out of balance with the sash weights. It would be nice to come up with a way to deal with the increased weight without having to disassemble the windows completely to install bigger sash weights, but that alone wouldn't be enough to make me abandon the idea.

Information, advice, comments?

Thanks,

Stan
 
We built our home in 1978 and put thermpane glass in all widow and doors We are now starting to replace them as they start to give us trouble.If I had a house with single pane glass I would replace whole window instead of replacing just sash. If you figure buying the thermopanes and tearing into frame to to do all repairs ( time involved) it would cheaper in the long run to by new.
 
We replaced our windows last year with vinyl replacement windows and they are great. We had double pane windows before but they were 25+ years old and let air in around the frames. The new ones will tilt in for cleaning and seal much tighter than the old ones. Once we learned the technique, it was no problem to remove the old sashes and put in the new windows. Plus it made a difference in the heating/cooling costs. Sid
 
Wouldn't be much gain. So-called "insulated" worked better depending on how far the two panes are spaced from each other. 1/2" is usually minimum and further is better. So you're talking about fitting in a least new glass 5/8" thick and more likely 3/4" to 1". For what you want- is why custom replacement windows are made. You take out the two sashes (assuming you have double-hung) and slip in the new replacement unit made for your size.
 
We put single pane windows in as we built. Could not afford high end windows. Came back later and put storm windows on the outside. Made all the difference in the world. On a cold windy day, if I open the old interior windows, you feel no cold air coming in. I used the ones you can open with a screen in them for when we want the windows open.
Best thing we ever did for heating and cooling.
Richard in NW SC.
 
replacing the glass might help a bit but with the old leaking casework around the nice new glass you wont gain much I put in new double hung windowsand I was surprised at how much air got in around the old window frames,it would probably be less work to replace the whole thing
 
It would be much simpler to just buy replacement windows from lowes, home depo, or your lumber yard. They don't have the outside flanges like new construction windows. Just remove your sashes and slip them in.
 
Replace the whole window, sash weights are no longer used, the weather stripping holds the windows up.
 
I think when double pane windows are made most mfgs use either Argon gas between the panes. If just air, I'm sure it's really dry air. If the seal between the panes breaks you'll start getting moisture between the panes and the window turns all foggy and the only thing you can do at that point is replace it.

Personally my replacement vinyl windows are nice but I might not make the decision to do it again. It was expensive having all my windows replace. I guess my old windows and storm windows were pretty good after all as I saw no change in heating/cooling costs. As they replace a sash with a window so to speak you loos glass area. The new windows don't open nearly as big--no escaping a fire through them. :) On the plus side they unexpectedly and surprisingly cut down on outside noise coming in the house. They are much easier to clean. They require no painting. I have a life-time warranty that they will be replaced even if my mower throws a rock through one.

If I were you I'd do like my neighbor, replace a few at a time and do it myself. Install storm windows on the others or at the very least use that shrinkable plastic sheeting to cover the window for the season.
 
You could modify the existing sash, and do what you describe. I don't know that the benefit of doing same will be realized in any great amount, you are in a more moderate or temperate environment, so the thermal transfer from a single pane to an insulated pane may not be prolific. Its certainly better than single pane glazing, and likely to not be all that difficult to do.

You would have to design the modification and check that everything works, so maybe you make a few sketches, detail it and see if anything is a problem.

If you can modify the wood sash to fit insulated glass, (speak with the local glazing or glass supplier) then detail the glazing pocket out for the new glazing. The glass supplier can provide you with the size you need. The area in the sash that is open and or clear is referred to as the day light opening or DLO, and that overall actual dimension should deduct for necessary room for the glazing,(expansion) a glazing gasket, glazing setting blocks if used or necessary. You don't want a precise and or exact/tight fit for the glazing, it needs a little room and your glazing supplier can help you once the dimensions of the modified sash are known. I'd want thin setting blocks on the bottom, a glazing gasket or something between the edge of glass and wood sash. Its possible you could pin the glazing with points or install a glazing trim/retaining piece or both like you mentioned, you do want to make sure the glazing is secure.

New windows would likely perform better seeing that the units by themselves will likely have better performance specifications, stand alone, but the installation is where it counts, so the rough opening and surrounding areas are insulated, and as a unit within the wall, as an assembly is where you get better performance. The best made window won't perform unless its installed properly.

I re- glazed a sizeable bow window that got hammeered from the elements about 15 years ago. The contractor doing some work here, said he could not do anything with it, has to be replaced, not only did I dis agree, I proved him totally wrong and literally rebuilt the window where the wood, (mainly the sill and the 2 operating sashe bottom rails) was deteriorated. Once that was done, I measured up and ordered all new glass, installed it using push points and glazing compound, primed and painted, its just now needing paint again, and though it does sit under a decent overhang, the weather from the west does get to it if its a strong thunderstorm or similar, so its well protected but gets the weather at times, there is one on the opposite side of the house, under the overhang and the unit is like new, but is of the '78 vintage.

In the bitter cold, I cannot feel much if any thermal loss or transfer, it was a lot of work mind you, but a rewarding project when I can see 40 miles out that window clearly and that following winter when the draft from it was eliminated.
 
They're widely available. I've installed them in site built windows many times, but always as large fixed windows. My question was intended to be specifically about the operational and structural issues of doing what I described.

During the period of time when super-insulated houses were being built or retrofitted in response to the first energy crisis in the mid 70's, I became quite knowledgeable about most matters concerning heat loss, heat preservation, indoor air quality, etc. I've stayed more current about windows than most of those other things, but this is something I've thought about for years but never heard about anywhere else. Undoubtedly such information exists elsewhere, but I like to get the opinions of the people on this forum because it's generally practical and unbiased.

Stan
 
Another vote for replacing the whole window. I wouldn't purchase the Argon fill, I worked for a major window manufacture and it really ain't worth it, I think the energy savings payback was something like 45 years. kinda like the nitrogen filled car tires. A gimmick, IMHO.
 
That's likely to be the way I end up doing it, but I wanted to explore the option of a different approach. In 2012 I replaced all the double hung wood windows the way you describe in a small rental house I own. Whether that part of the project required a building permit, I don't know. I didn't get one, and the building inspector didn't mention it when he came to inspect things that did require one---and he would have; he was thorough and not easy-going.

My current question is partly motivated, I'm sorry to say, by my feeling that the building permit that the City of Olympia requires for replacement of windows with newer versions of the same size and style of window is unreasonable. As far as I know, there is no inspection at any point in the process where useful advice could be provided, if indeed such a point exists. I suspect that except in the case of grossly misinstalled retrofits, the permit provides no benefit to anyone but the city and the assessor's office.

Stan
 
I would agree, either replace whole window or put on storms. I think you will lose about as much out the sides of the old windows as the glass, storms would help that.
 
Save a lot of time and money. Replace the entire window with thermopane, non opening solid unit. When I built this place in 2000 I made the mistake of buying the slide to open windows Big Ones. After 6 months in the country, I threw the screens away, locked them shut and they haven't been opened since. With the dust from the gravel road, bugs, manure, pollen, dust from pickers and combines Fresh air ain't fresh anymore. The AC provides clean conditioned air and the windows stay closed year round.
 
Stan, if you do change to thermo pane windows, check to see if there's some tax relief available for doing so. When I remodeled in '09, I got a tax break for my doors and windows.
 
He has to make sure they meet the Energy Star requirements. The line is still on the form. I obviously haven't done one yet this year. Likely he would have to buy complete new certified window units. I have never seen a credit come thru for re-manufacturing your own sashes. DMH-CPA
 
In histoic districts they would like the homes all to appear correct for the era. There are some egress issues in case of fire. But if there is no inspection then all it is is a MONEY GRAB by the city inspection dept/assessor. In the county I live, I live in the rural county. You have to buy a building permit, but no building inspection of structure. Only thing they inpect is the septic tank system, and of course square footage so they can jack up your property taxes. gobble
 
Why don't you just get the vinyl replacement windows that go right in your old frames. They seal up pretty well and would be way faster, easier, and probably cheaper. You want to at least cover the sills before you install and the later you can wrap the frames and be done painting. Easy do it yourself project. Takes about an hour per widow,
 
There used to be a Fed tax credit for improving your house, insulation, storm doors, better windows. Check with a CPA.

Trying to add another layer of glass to an old window may cause a film to build up between the two layers. If you still have windows with weights, good chance you have air leaks too.

Window world advertises on TV their replacement windows are around $200 installed. I know a guy who is pleased with their windows and work. He may have paid a little more $230 I think.

In 91 I replaced all my windows with Anderson Casements. They were way more than $230 and I installed them myself. Unlike double hung, casements have a seal and are air tight. I foamed in my window jams, absolutely no air leaks there either.

I believe investing in the tried and proven, Insulation, good doors and windows is better than investing in an expensive heating source or alternative heating source.
window world.
 
We had all eight windows in our house replaced with double hung by Window World two years ago. Total for the eight installed was $3900.

However, two of those were large three section picture windows.

Couldn't believe how much lighter and quieter it was in the house. Plus I'm sure we have saved some on propane.
 
(quoted from post at 04:33:06 01/19/15) Except for the front rooms, most of my house has double hung wooden sash windows. Has anyone ever heard of replacing the single thickness glass panes with insulated double glass units (often called "thermopanes" after the brand name)? It seems to me that the sashes could easily be rabbeted deeper to accommodate the thicker insulated units, and they could either be held in place with points and glazing putty or stopped in with wooden trim pieces. The main problem I can see is that the increased weight would be out of balance with the sash weights. It would be nice to come up with a way to deal with the increased weight without having to disassemble the windows completely to install bigger sash weights, but that alone wouldn't be enough to make me abandon the idea.

Information, advice, comments?

Thanks,

Stan

All the mullions I have seen are to not thick enough to babbit our for double pane. NOw if you are doing one single pane you could probably do it but for the time and money you could buy a whole window from Lowes or Home Depot.
 
What about an income tax credit?

What was the price of just regular single double hungs? Are they air tight? Worth it?
 
Thanks, George (I'm assuming Geo is for George, although I can't figure out what TH stands for). Your advice all seems good, but I believe you may have misunderstood part of what I am asking about. I wouldn't be adding another layer of glass to the existing window, I would be replacing the existing panes of glass with factory made sealed insulated glass units, commonly called thermopanes. Although any poorly made, poorly installed, or poorly maintained window can let in some cold air, when a good double hung wood sash window is properly installed and maintained, there are only a few places where there can be significant air infiltration. One is at the point where the upper and lower sashes overlap, and the other is where the lower sash rests on the sill. Both of these locations can be made considerably more airtight by the installation of some gasketing type insulation.

The issue of upgrading my windows at all seems relatively pointless right now. It's January 19th, and the daytime high temps today and yesterday have been in the 50's, the nighttime lows in the 40's. It isn't like this all winter, but it's within 10 degrees of this a lot.

Stan
 
Frank MN gave you the same advice I would give.
You can buy an insert that fits into your original frame.
You remove the inner stops, pull the sashes, remove the parting stops and pop the window in.
Then reinstall the inner stops and caulk.
Takes less than an hour once you've done a couple - more like half a hour.
They are all vinyl, tilt in for easy cleaning, insulated glass and only cost about $150 for a typical double hung.
I put 9 of them in one of my rentals and have put about 50 of them in other people's homes.
They love them.
Home Depot sells them. You have to measure and then special order them.
 
Hi Frank;

You're probably right that it would be faster to just replace the complete windows with factory made units. I would have to take each window apart much more carefully to do what I asked about than I would to pop in new windows that would cover up the areas damaged by quick removal. Whether it would be cheaper in dollars is a different matter. Two summers ago, at a different location, I replaced four small (as in 32X32) windows the way you suggested, and they cost me $860. I have ten windows to replace in my house, all of them larger than that---some by a considerable amount. I haven't priced raw insulated glass units in more than twenty years, but I would guess that they cost half the price of complete windows, or less. If so, the savings to me could be in the $2500 range.

Stan
 
That's likely to be what I end up doing, Ultradog. But, see my reply to Frank MN below. After I posted that, I remembered that I installed one more window at that same house. It was a special order unit from Lowe's. It cost $250. The other windows were smaller, but more expensive on a square footage basis because they were from a local glass company rather than a big box store. I got them because they were Milgard brand (locally manufactured, but sold in about 1/2 the U.S. & Canada) which have a lifetime guarantee, even on glass breakage. That seemed worthwhile for a rental house. So, if 5 small windows cost me $1100 in 2012, I would expect 10 larger windows might cost me $4000 to $5000 in 2015. That's enough to at least make it worth my time to look into alternative ways of doing it.

Stan
 
Stan,
Geo is short for George.
TH is Terre Haute, In.
Name and location.
I think that's what Window World does, is make replacement thermo pane windows custom fit to your window. Not 100% but I think they use your old window frames to keep cost down.
 
I read your reply to Frank.
Just so we are on the same page here; you do not remove the inner or outer trim. None of that is touched. You just remove the sashes and slip the insert into the original frame.
 
We got a tax credit on it, don't remember how much without looking it up.

The windows are air tight, and we consider them well worth it.
 
Shoulda mentioned the ones we got block UV rays which should keep furniture by windows from fading.
 
Yes, we're on the same page. That's the way I did it. What I said in my previous response to Frank MN was that I understood that it would take a lot longer to do it the way I was talking about than to just pop in new windows because if I was going to use the same parts again I would have to be more careful about how I took things apart. New double hung vinyl windows cover about 4" of width, so you don't have to be that careful about how you take things apart in the area that's going to be covered. That makes it simple, and simple makes it fast, and time is money, and etc. But if other considerations were equal except that replacing my windows one way would take me two days, and doing it a different way would take me a week but save me $2000, I'd view that as three days' work for $2000, which is more than I usually make.

Stan
 
Rarely does, David. Jobs always look easier and payoffs always look bigger from the front end. But it's pretty late for me to start being a realist now.

Stan
 
Back in 91, Anderson called the windows low E. They blocked heat loss due to radiant heat loss.

I recently did an addition using low E windows. I made a sun room, room on south with 4 windows. Don't get the solar gain I would have with regular windows, but don't lose the heat at night. All most and even trade.
 
Best thing I ever did in my 100 year old farmhouse was install all thermopane windows. Check with your power company they might give a credit.
 
Window World does not have a very good reputation here. In fact its down right bad. The ones I had them quote before I found that out were a complete unit, not just the windows themselves, and no offer was made for just the windows. I had a local guy do mine and he was about a grand cheaper. I think mine are Brenmars or something like that. Lifetime warranty, even if you break one. They will replace it free for as long as you own the home.
 
The problem with that fix is you still have the old and leaky casework around your nice new inserts. A good friend went that rout and reggretted his decision. And also the inserts make your window smaller because the framework around it takes up a couple inches so you end up with less window and more framework .
 
I doubt you will ever see a payback from it, I am reaching that point also. I do believe as much energy is lost through fenestration, air flow, around old windows as the glass conducts. I would want to make sure it is foamed back to the studs. That would be my concern with leaving the weights in there.
 
David;

Explain that to me in more detail, if you would. As I sit typing this, I can look left or right and see some of the windows I'm talking about. All of them appear to be caulked at the trim to wall juncture then painted so that they look like they would be airtight. These particular windows have some different system than sash cords and weights---something that was probably hot stuff in 1950---but let's talk as if they did have cords and weights. Except for the holes where the cords pass over pulleys to the weights inside the frames (if we pretend that these windows used that system) the windows seem separated from whatever space might exist on each side of them. Even if there is no insulation in the space between the side of a window and the nearest stud, what air flow will occur? I understand that a sealed but uninsulated exterior wall will cause a room to lose heat through radiation, but that's a slower process than if there's an actual draft, isn't it?

Anyway, I share your opinion that it's unlikely that we would see payback for costly window replacements in whatever amount of time we are able to stay in this house.

Stan
 
C.R.

See my last reply to David G below, because I'm still unclear about the nature of the leaky casework issue. I'm not trying to argue, I'm trying to understand and learn.

When I replaced double hung wood sash windows with vinyl insulated windows in a rent house a few years ago, I caulked the seams in the wood window casings that would be hidden by the new vinyl windows. Then I caulked around the vinyl windows before I installed the stops, then caulked the joints where the stops met the vinyl. The window trim was caulked at both edges on all four sides, both inside and outside the house. Where would my casework be leaky in that installation?

As for the reduced viewing area because of the width of the vinyl frame, that did occur with the windows I replaced and it was a problem because they were already small. There, it wasn't a bad tradeoff because the new windows looked ten times better than the old ones, and they insulated for both heat and noise. If I were to put new windows in the existing frames in the house I live in, the loss of glass area would be less critical because the windows are much larger.

Stan
 
I only know of one person who used WW. He had them installed in a rental duplex. Very pleased with work and price around $230 each.
 
Yes, I understand that.
But the other options are?
It nice to have new windows - installed with nailing flanges to the sheathing and that sticky tape stuff to seal the flanges (I forgot what it's called) then foam them in to the rough opening. But we all know that involves dealing with siding, interior trim and probably plaster repair. I'm just thinking the most bang for his energy buck is the inserts even though there are disadvantages and compromises there too.
 
I guess every house is put together differently,in this one there were small cracks in between where the wooden parts of the framing came together I suppose after 100 years the wood dried out and shrank up some.also I had a couple of areas where the wood had started to rot. I am fortunate in that my place is a single story,so when I change a window out Im not trying to play Tarzan. the new pre hung windows have a wide nailing flange and there is a tape that goes on to really seal things up tight. I has a spot in my living room where two windows were side by side and the place where they came together allowed a LOT of cold air into the house,and the new windows are tight enough that I no longer have to wrap the windows in plastic in the winter
 

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