Wooden (House) Windows--- A Question

[Alan D. Hyde]

I learned how to build houses as a boy the way that many, perhaps most, people have learned: from older more experienced people, by watching and by doing, kind of through an informal apprenticeship.

The kind of houses we built or restored had traditional, for New England, double-hung wood sash windows.

Now, my grandfather put casement windows in the house he built, and I also like casement windows. His house has painted steel casement windows, which are strong and low-maintenance, but which transmit a good deal of heat and cold into the house through conduction. For energy conservation purposes, I think wood windows would be better (less conduction).

So as I design our next house, I'm looking at using casement windows, probably as part of a "Christian window." That's a pair of casements separated by a stone or wood "t" (cross), often with smaller windows above the cross-bar of the "t."

I've been looking around at architecture and house construction books, and haven't seen much on this (mostly, I suppose, because few build their own windows anymore). Here's a photo of the kind of window I'm talking about:

http://www.adanor.co.uk/108-0808_img.jpg

Can anyone suggest any books that cover the design and construction of such windows? In wood or in stone? (I think I may be able to get a deal on some good limestone :D ).

Alan

[ 05-05-2003, 05:02 PM: Message edited by: Alan D. Hyde ]

[Bruce Hooke]

Are you actually planning to build the windows from scratch (i.e., from a pile of wood) or are you planning to install four standard casement windows to create the "Christian Window" (or two casements under two fixed windows or one double casement under a double, fixed window)? Unless you really want to build your own windows, I think a system that uses standard windows would produce a better end result and I don't see any reason why you couldn't get the same look. There's quite a range of windows available stock...

[Alan D. Hyde]

Bruce, from the windows I've seen, the prices are so high that I think I'd prefer to build my own. It's not rocket science (or engineering :D ) and I'd save quite a bit.

Alan

[ 05-05-2003, 05:35 PM: Message edited by: Alan D. Hyde ]

[Ed Harrow]

Alan, before you go too far down the casement route, consider that it's difficult to get ventilation with casements when it's raining (unless, of course, you have a large overhang or awnings).

If you've not looked at it, do examine the book "A Pattern Language". It's well worth your time and trouble. It doesn't discuss building windows, but it will talk about windows and their placement.

Sounds like a fun project. Ed

[Nicholas Carey]

Originally posted by Alan D. Hyde:
So as I design our next house, I'm looking at using casement windows, probably as part of a "Christian window." That's a pair of casements separated by a stone or wood "t" (cross), often with smaller windows above the cross-bar of the "t."

I've been looking around at architecture and house construction books, and haven't seen much on this (mostly, I suppose, because few build their own windows anymore). Here's a photo of the kind of window I'm talking about:Think about ordering windows: You'll get windows that are far more energy efficient than what you could build yourself -- which will more than pay for itself over the life of the house.

What you want is a pair of casement windows with a transom(s) over them. A romp through the window catalogs and a visit with a window specialist ought to find what you're looking for. Plus, a window manufacturer should be able to build to spec as well.

[Chris Coose]

Alan,
I wonder why you are moving from that house.
Need something larger?

[ 05-05-2003, 05:47 PM: Message edited by: Chris Coose ]

[Alan D. Hyde]

Not mine, Chris. Just an example of the window type. That's the front side of Chartwell, Churchill's house in Kent; most photos of Chartwell seem to be taken from the back.

We're in a brick Cape Cod now, fairly capacious for the design (no Gunston Hall, though), but built back in 1941 when closets were much smaller, there weren't as many bathrooms, etc.

Besides, it's always a pleasure (though sometimes a trial, too) to build something. That's why we're on this site, right? :D

Alan

[ 05-05-2003, 06:16 PM: Message edited by: Alan D. Hyde ]

[High C]

Alan, I once owned a house that had about fifty large, modern, wood casement windows. I enjoyed them, with one exception. They have their screens on the inside. I found this somewhat unatractive, so I removed the screens from windows I knew I would never open, about 3/4 of them. And yes, they are very expensive. A lot more than a double hung.

Be sure you don't skimp on the thermal pane glass. You can't just use two panes of glass and hope for the best. The moisture that is trapped inside will fester ang gradually cloud the inside of the windows. Any decent glass place can make up the double paned glass for you to fit into your custom made windows.

[Bruce Hooke]

Having worked on a house where the owner-builder used old sashes from double-hung windows but reworked them as casement windows I can offer some insights into the problems you need to consider.

- If you plan to open the windows then you will probably want screens. If so then the only place to put the screens is on the inside of the window. The fancy mechnical linkage used on commmercial casment windows are therefore very nice because they allow you to open and close the window without removing the screen.

- It is very nice to be able to open the window as little or as much as you want and have it stay there. To do this you again need some sort of mechanism like the one used on modern casements.

- To get the window to seal tightly against a gasket, which is important if you are interested in energy efficiency, you need some sort of catch that pulls the window tightly closed against the gasket. Again, for ease of use you don't want to have to remove the screens to do this.

- For ease of window cleaning, and similar things, you want the screens to be easily removable.

- As mentioned abov, good gasketing is key for efficiency.

If you want to build basically modern casement windows then I would get catalogs from commercial window suppliers. These catalogs provide a lot of detail on the construction of the windows so you can basically use their design. But I'm not sure how you will deal with the mechanisms used to open and close, and lock the windows.

If you don't care about the modern features then you might want to try to track down a carpentry book from 100 years ago, when making casement windows would have been more common. I don't think you will find much currently in print on building casements windows because for anyone who charges a customer for their time it is much cheaper to buy commercial windows. Even the owner builders I've known have either used commercial windows or recycled windows...

BTW - In the house I worked on all of the "modern" features I listed above were skipped - To open or close the windows you removed the screens. A long hook was used to hold the windows open and a short hook to keep it closed so there were basically only two options - open or closed. It was all just part of living in a house on an island, with no running water, solar power for the electricity, and that was built out of mostly recycled materials. It's a great place but it is more work to live there...

[Nicholas Carey]

Originally posted by Bruce Hooke:

- If you plan to open the windows then you will probably want screens. If so then the only place to put the screens is on the inside of the window. The fancy mechnical linkage used on commmercial casment windows are therefore very nice because they allow you to open and close the window without removing the screen.Or you can get inward opening casements, with the screens on the outside.

[Bruce Hooke]

Originally posted by Nicholas Carey:
</font><blockquote>quote:</font><hr />Originally posted by Bruce Hooke:

- If you plan to open the windows then you will probably want screens. If so then the only place to put the screens is on the inside of the window. The fancy mechnical linkage used on commmercial casment windows are therefore very nice because they allow you to open and close the window without removing the screen.Or you can get inward opening casements, with the screens on the outside.</font>[/QUOTE]True, and now that I think about it, I think this is how some of the windows in the house I worked on were set up. The problems with this solution include: the windows take up space in the room, you can't put plants or anything else inside the windows, they don't do anything to keep out rain if they are open at all (in my experience out opening casements can be left open a couple of inches in light to moderate rain), and you still have the problem of compressing the window closed against a gasket and the problem of how to hold it open...

[Oyvind Snibsoer]

Could someone please enlighten a foreigner on what a casement window is? All the windows in these parts are either hinged on the top or on the sides. "Christian" windows, which are quite common on older houses, have separately opening, side hinged windows. Modern windows usually have a more elaborate hinge system where the window swings out horizontally and can then be flipped around completely so that the outside of the window can easily and safely be washed from inside the house. Originally marketed as "housewife windows" up until the early '80s, BTW. These windows can also be left at least partially open in a storm without allowing any rain into the house.

We rarely bother with screens on our windows, BTW, though rural areas certainly have their share of mosquitoes in the summer.

[N. Scheuer]

You rang? (I'm a "Window Man")

First, (for Oyvind) a "Casement" window in America is one which is hinged along one jamb (vertical frame member) with a latch mechanism on the opposite jamb. They often appear in pairs, left and right handed, withing the same opening.

In more recent years Casements almost always have a crank-operated opening mechanism which will hold an "open" sash at any angle against a wind load. Originally Casements were fairly narrow, especially in pairs, and had only a simple "push-out lock handle.

Windows throughout Europe follow diferent conventions, with sliding windows being common in some places, the "H-Window" (rolls over, upside down for cleaning) common in Scandinavia, and combination side-hinged/top-hinged windows common in Deutchland.

The Double-Hung window (both sash able to slide vertically) or Single-Hung (only the bottom sash slides) is more common in America than anywhere at this point. The culmination of this type of window can be seen at Tomas Jefferson's home, Monticello, where he designed Tripple-Hung windows for his dinning room. The two lower sash exceed the height of an average man, and so when they are elevated to the top, they form a pair of walk-through passages out onto a large balcony.

If only the top sash is lowered in the dinning room, guests may dine with a lot of ventillation, but no wind to blow their napkins around.

In an Architectural book describing the various sorts of windows one might choose, I read that, "Sliding windows are to be considered so inferior that I won't waste your time describing them further here". "There is no good reason for choosing sliding windows."

Now for Alan: The old steel casements, like my Father has in his home, are very innefficient, both from the steel sash and frame, and from the single-pane glass. The more modern PVC windows, with their insulating glass, can be very efficient.

In our new addition we have wood, with aluminum exterior covering, insulating glass casement windows made by Pella. They are a very good quality window.

One difficulty with insulating glass is the "reveal" of the joining materials around the perimeter of each pane. If many small lites are desired, the edge materials will require muntin bars to cover them that will appear much too wide. So what is commonly done is to have just a single large pane, with a grill-work of fake muntin bars which snap in-place on the inside ofthe sash. "They all look the same from the street" is the byword of the industry.

The harware for operating modern Casement windows in the USA is generally very high quality.

One aspect of double Casements that I especially like is the scoop effect when one sash is opened to catch a breeze that blows parallel, or almost parallel, to the side of the house. In this respect they are vastly superior to Hung Windows, which only vent well for straight-on breezes.

Have fun, Moby Nick

[N. Scheuer]

BTW: I would consider the windows in the photo Alan included with his initial post to be an exceptional piece of design work. Too many people settle for way less these days.

Moby Nick

[Nicholas Carey]

Some data points on window energy efficiency.

The Efficient Windows Collaborative (http://www.efficientwindows.org/) says that with proper window selection, one could cut annual heating/cooling bills by more than 1/3.

They have a nice page set up where you can compare energy costs for different window types for your location. It takes into account factors such as energy costs, etc. http://www.efficientwindows.org/selection.cfm

They also provide a link to RESFEN (http://windows.lbl.gov/software/resfen/resfen.html), software to model residential energy consumption, based on all sorts of different factors:


Using a computer program such as RESFEN to compare the performance of window and skylight options allows you to customize the calculation by adding heating and cooling costs for your specific climate, house design options, and utility rates. The user defines the house with a series of selections from a menu: location, heating and cooling system type and efficiency, utility rates, floor area, window area, window orientation, interior/exterior shading, etc. A specific window or set of windows for each orientation is selected and specified by their U-factor, SHGC, and air leakage rate. The program then calculates the annual energy use and cost in a matter of seconds. RESFEN provides the annual heating and cooling energy use and cost as well as peak heating and cooling loads. It is designed so that different window types can be placed on different orientations. More information about RESFEN. (http://windows.lbl.gov/software/resfen/resfen.html)Hope this helps.

[Mrleft8]

As a long time builder, I can tell you that both wood, and steel windows are very bad. (Very, very, very, bad!) In this industry, we suggest glass for windows. Glass is very easy to see through, if kept clean. It also allows solar radiation to penetrate a building, to heat it during daylight hours, unlike steel or wood..... Just some thoughts from a pro.... :D

[Bill Perkins]

Alan the mass production of high quality windows is truly one of the advances of modern construction . You can't produce good double pane ( with an inert gas sealed in between ) in your home shop .

As Nicholas said ,I think you'll end up with a unit composed of a pair of casement windows with a pair of awning windows above ,separated by wood ( or stone? ) trim . I suggest you get hold of a catalogue from Marvin Windows .These are high quality and Marvin is good about carrying awning windows of a width that matches every casement window width they carry . This gives you maximum design flexibility and is not the case with all brands .

[Wayne Jeffers]

Alan,

I share your thoughts on this. Production windows today seem very over-priced. If one could obtain good stock, it should not be that difficult to produce good quality windows. With planning, you could set up a production sequence to produce parts for many windows at once, to minimize machine set-up time. It seems to me that one could produce enough windows for a house with a week's work time, at a savings of thousands.

Maybe I'm a Luddite, but I don't think much of double-pane windows. I don't know how much resistance to heat flow is created by the thin space of inert gas between the panes, but it seems negligible. Especially in light of the expense involved.

If I build another house, I will have old-fashioned wood double-hung windows with old-fashioned storm windows. With 2X6 or 2X8 walls, I can get a very substantial air space between the panes. In my experience, this is vastly better than double-pane for avoiding heat-loss and sweating windows. :mad: (I don't think this can be done in a practical manner with casement windows, however.)

Wayne

[Bruce Hooke]

Originally posted by Wayne Jeffers:
Maybe I'm a Luddite, but I don't think much of double-pane windows. I don't know how much resistance to heat flow is created by the thin space of inert gas between the panes, but it seems negligible. Especially in light of the expense involved.

If I build another house, I will have old-fashioned wood double-hung windows with old-fashioned storm windows. With 2X6 or 2X8 walls, I can get a very substantial air space between the panes. In my experience, this is vastly better than double-pane for avoiding heat-loss and sweating windows. :mad: (I don't think this can be done in a practical manner with casement windows, however.)

WayneBased on all the numbers I've seen, both from the manufacturers and from external sources such as books, double-pane windows with inert gas inbetween the panes are hugely more efficient than single pain windows, even where you have a good storm window well outside the inner window. An air space isn't that big a help in terms of providing insulation because the air moves around in that space and carries the heat across the space, whereas inert gas is, as I understand it, is much less efficient at transferring heat so even a small gap so it works much better as an insulator.

[Wayne Jeffers]

Bruce,

Based on my limited knowledge of chemistry, the prominent feature of inert gasses is that they will not react chemically with other gasses. I assume inert gasses are used between double-pane windows so that they are less prone to fogging.

I can't imagine how inert gas would provide less resistance to heat flow than any other gas at the same pressure. If there were a vacuum between the panes, that would provide some measure of increased resistance to heat flow.

In my experience, double pane windows sweat a lot in winter, unless there is a lot of positive air circulation around them. The windows in my house now sweat little or none, even though they have aluminum frames, because I have about a five-inch air space between the windows and the storm windows.

The worst I ever saw was a house I had built in 1975. I let the builder talk me into double-pane glass instead of separate storm windows. These also had aluminum frames. It was a good thing this house had marble sills, because I was able to keep towels on the sills all winter to catch the run-off and keep it from running down the walls. This problem was mostly due to the aluminum frames, but also due to the double-pane window glazing sweating.

The place Michelle lived when we met four years ago had new double-pane windows with vinyl frames, and they were also terrible for being both sweaty and drafty.

Wayne

[Alan D. Hyde]

Probably I should have mentioned that we only heat our house from November 1st to March 1st, unless we have exceptionally unseasonable weather for a day or two. Even on such days, we're most likely to just build a fire or two.

I don't much care for modern sealed-up houses, and have noticed that heating expense rises dramatically once you attempt to heat a house past 59 degrees.

I was in England during 1970-71 and my house, and most other houses, were back then kept at 55-65 degrees (F). It's much more economical to wear a wool sweater than it is to keep a house at 72 or 75, as many do here in the States. A less hot and dry house in winter promotes less respiratory infections, and is generally healthier. (Anyone else here know about "sleeping porches?") Besides, remember how the English girls back then had nice rosy cheeks?

Radiant heat, by the way, stands a few drafts much better than does forced air.

Also, heat and cold are transferred by conduction, by convection and by infiltration. So I think Wayne's comments do have some sound basis in fact.

Alan

P.S. Imagine a flat steel strap, about 3/4" x 16" x 1/8" attached through a hole by a staple to the lower rail of the casement frame and perforated with holes every inch or so at the other. The top of the staple runs parallel to the window stiles, so the strap can pivot on the staple from side to side. Depending on how far you want the window open, you place a selected hole in the strap over the steel peg protruding up from the bottom of the window (sill) frame.

Vinyl screens could be attached by Velcro (TM) to the inside of the window surround.

Scavenged sash windows can be made into tolerably good casement windows without much effort, as was mentioned above. This is what I did on the 10' x 12' playhouse we built for our youngest daughter. So far we have just under $100 in the whole thing--- most of that in tar paper, shingles, and roofing nails for the roof. Much of the rest was saved from an about-to-be-demolished pre-Civil War barn. The foundation is stone and re-used old railroad ties ("sleepers" for our UK contingent :D ).

[Wayne Jeffers]

Originally posted by Alan D. Hyde:
. . . Radiant heat, by the way, stands a few drafts much better than does forced air. . . .
If I were to build another house, I would also be tempted to install an old-fashioned gravity-circulated hot water radiant heating system. (Living out in the country like we do, we occasionally lose power for long periods.) Biggest problem is that I'm not sure I could find anyone these days who understands the design technology well enough to set up a system to work properly without a pump.

Kudos, Alan, for keeping your house cool in winter. I agree on the health benefits. I generally keep my thermostat at 67 during the day and 60 at night. Michelle thinks that is too warm and the children think it's too cool. :rolleyes: To my dismay, I work in a "modern" office building where the wintertime temperature is about 78 to 80 degrees in the winter. :mad:

BTW, RR ties also were called sleepers in this country in the early days of railroads.

Wayne

[N. Scheuer]

(for Wayne J.) Why inert gas?

The reason Argon Gas is injected into the space withing insulating (double pane) glass to replace the natural air is that Argon will not transmit caliries as quickly as natural air will.

A vacumm would work even better, except that the average window glass is not thick enough to withstand the atmospheric pressure pressing in from both sides, were the cavity between panes vacummed out. So the air need to be replaced by an inert gas of equal pressure.

BTW, a lot of window people will counsel against the use of Argon. It will not do as much for window efficiency as low-E glass will. Furthermore, if the window mker cheats you by not really injecting enough gas, or if it leaks out and is replaced by air, who's gonna know? The gas is invisible!

Moby Nick

[Wayne Jeffers]

Thanks, Nick.

I wonder what the differential is for Argon vs. atmospheric air in terms of transmitting calories (heat.) I suspect the difference is small. I note Argon has an atomic number of 18, so it's not appreciably lighter than the atmosphere.

The gap between panes is maybe 1/4 or 3/8 inch. How much difference can that make? In any event, I've never personally found the results satisfactory.

I've suspected that coatings which reduce radiant heat transfer have more effect than attempts to reduce conduction.

Wayne

[Bruce Hooke]

A few miscellaneous thoughts in response:

- Alan, I can see where in your area heating from only Nov. 1 to March 1 would be quite viable. Here in Rhode Island the average night-time temps were running well below zero until early April this year, so that clearly colors my experience to some degree. If I turned off my heat on March 1 I would have a lot of frozen pipes! I would, however, ask how often you use AC because in warm climates that is often at least as important as heat in terms of energy usage relative to home insulation. I don't use AC at all but I'm not sure if I would or not in your area.

- Inert gas does, in fact, make a significant contribution to increasing the insulating value of the window. Based on my understanding of chemistry it has to do with the ability of different gases to 'hold' heat (in the world of solids, this is why most metals feel much hotter and colder than wood even if the real temp of the material is the same). Here is a website with more details although it unfortunately does not go into much detail on the why part of the question:

http://www.advancedbuildings.org/main_t_building_inert_gas_window.htm

- As to the condensation problems, my guess is that the real reason that you had sweating with the double-glazed windows and not with the single-glazed windows (aside from the aluminum frames, which are definitely a problem) is that the house with double-glazed windows was probably much better sealed than the house with single-glazed windows. If a house is very well sealed then you can reach a point where you need to provide some designed ventilation to get rid of excess moisture. Otherwise you run into problems like the ones you encountered. Older homes are leaky enough that the moisture escapes on it's own - often around old, leaky, single-glazed windows. This can get into the whole debate about whether it makes sense to build houses that are very well insulated and sealed, but that's a different question. BTW - In a house with storm windows and single-glazed inner windows there are often condensation problems inside the storm windows because this is not a sealed space.

- Alan, as to your solution to holding the window open, I think I follow roughly what you are talking about. The one piece I can't fit together is how this integrates with the screen - can you use this system with the screen in place without leaving a hole for bugs and can you adjust how much the window is open without removing the screen - and does that matter to you?

Understand that I have no objections to re-using old materials and designs and coming up with neat ways to solve problems that don't call for using fancy new products, but I think anyone going into building a house should do so with their eyes open and with a good understanding of the impacts of their decisions. Also, I've seen owner-builder projects where the project got bogged down by the owner-builder trying to do everything in their own special way and in so doing making the project almost endless. And I've seen such projects become marriage-destroying, life-sapping albatrosses -- so I get nervous when someone sounds like they might be headed down that road.

[Bruce Hooke]

Originally posted by Wayne Jeffers:
Thanks, Nick.

I wonder what the differential is for Argon vs. atmospheric air in terms of transmitting calories (heat.) I suspect the difference is small. I note Argon has an atomic number of 18, so it's not appreciably lighter than the atmosphere.

The gap between panes is maybe 1/4 or 3/8 inch. How much difference can that make? In any event, I've never personally found the results satisfactory.

I've suspected that coatings which reduce radiant heat transfer have more effect than attempts to reduce conduction.

WayneIf I reading this website (http://pump.net/thebasics/physpropgases.htm) correctly, the heat capacity of argon is about 60% of the heat capacity of air. Remember that the process by which the heat is being moved in this case is roughly as follows:

1. The glass is warmer or colder than the gas right next to it, so the gas molecules that are touching the glass are warmed up or cooled off by the glass.

2. The gas molecules either in turn warm up or cool off the other molecules next to them until the other pane is reached, or they move around until they are touching the other pane (I'm pretty certain that the latter is the much bigger factor).

3. Finally, the gas molecules touching the other pane in turn heat up or cool off that pane, completing the heat transfer.

Assuming I am correct in step 2 that the circulation of the gas is the much bigger factor, the addition of extra space between the panes does not have a big impact, because the heat gradient within the gas between the panes will already cause the gas to move around a good bit, thus transferring the heat from one pane to the other. The added time it takes for the gas to move between panes spaced 1/2" apart versus 5" apart is, I think, pretty insignificant.

[John Gearing]

Bruce,
I grew up in Connecticut in a house that was built in 1850. Wood sash windows, but without the counterweights. Always very drafty in the winter. We used to go around with Dad helping him seal the windows with that caulking cord material. That helped some. After about 20 years he invested in storm windows, and we had exactly the problem you are describing. In the winter, moisture would get caught in the space between the window and the storm window and condense on the interior surface of the storm window, usually as ice. When it melted it would run down onto the sill. Eventually this raised havoc with the wooden sill. SWMBO has modern sealed double-pane windows in her house, both fixed windows and opening windows (casement), and as far as I can tell from 3 winters' experience, they work fine. No doubt, however, that the more glass you have the more heat loss from the building. Once upon a time I worked in a bookstore that had huge plate glass windows, single pane, and in the winter you felt constantly because so much heat was being lost through those windows that it chilled you as well.

[Wayne Jeffers]

Bruce,

I found an Andersen Windows web site that said that Argon conducted 30% less heat than atmospheric air. If the gap were more than a fraction of an inch, I could more readily accept that this would make a meaningful difference.

The air between the windows will have a slight temperature gradient from the warm side to the cool side. Presumably with the Argon this gradient will be 30 percent steeper. It's the same principle as if you heated one end of two similar bars of different metals, one of which conducts heat better than the other. The bar that conducts heat better will be warmer on the far end than the one which conducts heat less. But either far end will be warmer the shorter the length of the bar (space between panes.) It is true that convection and associated heat transfer may increase with the increase in distance between panes, but I suspect convection will not offset the benefits of the increased space.

For walls, styrofoam has about twice the R-value (resistance to heat conduction) per inch as fiberglass bats, just like Argon is better than air. But if I have ten times the thickness of fiberglass (5 inches vs. 1/2 inch), the fiberglass is more effective. In a fluid medium, such as air, the value of the increased distance may be offset in part by convection, but only in part.

I think my current house with the single pane glass is more airtight than the house I had such sweating problems with in the late 70's. I remember, too, that I had problems with the double-pane glass in several panels becoming unsealed and the window fogging up. An expensive replacement, at that time. And the double-pane sliding glass patio door was a nightmare!

I have only one window where I have a bit of a wintertime condensation problem between the window and the storm window. It's the one where the inner window doesn't seal so well as it should. The outside air is so dry in wintertime that imperfect sealing around the storm window doesn't seem to cause sweating between the panes.

Maybe they've improved double-pane glass a lot in the last 30 years, but based upon my experience it's a risk I would not take again for the expense involved. Your mileage may vary. smile.gif

John,

Clearly you can't put tight storm windows on an old house with leaky inner windows, else you get the sweating problem you mention. There's little to impede the flow of moisture to the space between the windows. With tight inner windows, separate storm windows will not cause a problem.

The tighter windows need to be on the living side of the house (where the moisture originates) to avoid these problems. It is for this same reason that the vapor barrier on insulation in your walls must go on the living side, else you get sweating in the walls.

Wayne

[Bruce Hooke]

Wayne,

I'm working on memory here, but I believe that, in most gases, convection accounts for over 95% of the heat transfer. I don't think that convection increases much with increasing distance between the windows, I just think that increasing distance doesn't help much because of the relative insignificance of conduction.

You've hit it right on that the storm window needs to be leakier than the inner window to prevent condensation problems. Unfortunately, a house with leaky inside windows is exactly where you'd like to have tight storm windows...

I, of course, can't speak to the specific situation of your earlier house that had double-glazed windows with condensation problems because I don't have anywhere near enough information. There could be all sorts of explanations, such as hidden reasons why that house produced more moisture. I wonder if the metal frames weren't cooling off the adjacent inside glass and thus causing more condensation on the glass -- I think that's quite likely. Certainly, if you had double-pane windows that had metal frames with no insulating gaps in them, and had problems with the glass losing it seal, then it sounds like the windows in question were pretty low-quality.

I spent a few years in the remodeling industry and we installed a lot of windows. The only time I remember installing single-glazed windows was in garages and other unheated spaces. If any of our customers had encountered condensation problems in any of the double-glazed (or single-glazed) windows we installed then I'm sure we would have heard about it, and I don't remember any such compliants. So, I think your experience is the exception not the rule, but given your experience I don't blame you for being wary...

- Bruce

[Ron Williamson]

Often,sweating is due to the heat source.If you have electric baseboard heat or some source that doesn't use room air for combustion(like a woodstove or an old style furnace)and inadequate ventilation(or you keep the room temp too low),your windows will sweat.This is the reason that heat recovery ventilators are a building code requirement here.
I have problems spending very many thousand dollars on vinyl windows that are disposable after about 15 years.The plastic and weatherstrip and thermal units all seem the crap out.

Pella used to make(and might still)windows that had two panes,with the outside storm pane ventilated and removeable.We just worked at a place with this type.After twenty years,a coat of paint made them like new.
R

[N. Scheuer]

Window Pane Factoid:

The optimum separation between panes of insulating glass is about 9/16" to 5/8".

The next step toward insulating value, yeilding a quantum leap in thermal performance, is to use triple panes. The same performance can also be realized if the middle pane is merely a thin sheet of transparent Mylar Film. This type of window requires special machinery to stretch the Mylar, so samall shops simply use three panes of glass, and two sets of seperator bars. Even easier to use is a product from Tremco called "Swiggle strip". It is a licorice-like strip of mastic with a corrugated metal buttress material incorporated inside the mastic.

Moby Nick

[Wayne Jeffers]

Nick,

I have no particular opinion on triple-pane glass, but I remember on an Andersen Windows web site I found yesterday seeing a reference that spoke unkindly about triple-pane, i.e., big increase in weight and little increase in thermal performance. http://www.renewalbyandersen.com/window_basics/glass.asp

I'm naturally skeptical due to my unfavorable, though limited, experience with double-pane glass without separate storm windows. In a few moments Googling this morning, I'm tempted to conclude that 1) there is a lot of snake-oil in the window business, and 2) thermal benefits come far more from low-emissions coatings than from double-pane/gas-fill technology.

On a couple of sites, I found mention that argon gas is used to enhance the benefits of low-e coatings and that without low-e coatings, the increase in thermal performance from argon filling is pretty small. http://www.tlwindows.com/GlazingSelection.html http://www.advancedbuildings.org/main_t_building_inert_gas_window.htm

Several sites explained that the benefit of argon derives from the fact that argon is heavier than air, therefore it is more viscous, therefore it yields less or slower convection, thereby slowing the heat transfer due to convection. For example: http://www.simonton.com/architect/glass/lowe/

Apart from leaks around windows, heat can be lost/gained by convection, conduction, and radiation. In a plain double-pane window, I suspect that convection accounts for the least heat loss of the three. I have a hard time believing that the difference in viscosity between argon and air is so great as to reduce convection to a measurable degree.

I note on the Andersen site from the link above, they give the R-value of single pane glass as 0.9 and the R-vale of plain double-pane glass as about 2. I interpret this 2 to be two times the single pane value (2 X 0.9) or 1.8, leaving about R 0.2 for the air space between. Based on their statement that argon transmits only 70% of the heat compared to air, I would estimate that the gap between the panes would be about half again more resistant to heat flow compared to air, or R value 0.2 X 1.5 = R-value 0.3. This provides a net gain of about R-value 0.1 for the argon gas. Since Andersen claims that their low-e coated, argon-filled, double-pane units have R-values between 3 and 4, I assume the remaining gain in R-value gain (of between 0.9 and 1.9) comes from the low-emissions coatings.

This analysis comes only from about 20 minutes browsing the claims of major window manufacturers. I make no claims of window design/engineering expertise on my part.

I have no doubt that plain double-pane windows are marginally more effective at reducing heat transfer compared to a single-pane window without a separate storm window. Last I checked, single-pane glazing was dirt cheap and double-pane glazing was very expensive. Until I see far more convincing evidence than I've found to this point, for my money the cost-benefit analysis points solidly to quality single-pane windows with separate storm windows (and low-emissions coating) if I'm in the market for windows again.

(Another slow day at work. Does it show?) ;)

Wayne

[Oyvind Snibsoer]

In this frigid corner of the world, 3-pane glass is now the rule in new houses.

I actually have some personal experience with the lesser heat capacity of Argon. Back in my student days, I was involved in some rather hairy SCUBA wreck diving to only a little less than 60 meters/200 ft. Diving in drysuits in November, with a bottom time of 20 minutes and decompression time of around 35-50 minutes, you'd be pretty cold by the time you surfaced.

Of course, some bright guys from the physics department suggested we press out as much air as possible when we got to the first decompression stop, and then fill our suits with Argon. It worked extremely well, you could actually feel how the area on your chest around the suit inflation valve felt warmer as the Argon entered the suit.

Another thing; I believe the gas in double- or triple pane glass is heated before sealing. The pressure drop when the gas cools further enhances the insulating properties of the glass, there being less molecules to transfer the heat gradient between the panes. An added bonus for the manufacturer is that this would require less gas to be used.

[N. Scheuer]

Wayne:

I can't give much in the way of hard engineering figures for Argon gas in windows, but I am sure that triple-pane glazing is far better than Argon between two panes.

I just remember from my window days that triple-pane windows with low-E coating could easily be justified, as far as energy efficiency, for use on the north side of a building in winter.

One thing to keep in mind in regard to low-E coating is that there are two ways it is commonly used, "northern" and "southern", depending whether it is summer heat and air conditioning that requires optimization, or winter cold, and heat loss.

First of all, low-E coatings reflect long-wave radiation (heat) and transmitt almost all of the short-wave radiation (light). So in a southern climate you want the coating (typically ony one surface of the four in question) on side-3 (counting from inside, outward), or on the inside before it is able to heat up the air or gas in the cavity between panes. In a northern climate you want to reflect interior heat from surface-2, or the outside surface of the interior pane, before that heat can be lost by contact with the outer pane, which can be very cold to the touch.

Since glass is usually made into insulating glass panels in fairly small, discreet markets, an individual vendor will commonly make all of their glass the same. I'm more acquainted with the northern aspect of insulating glass windows.

You can tell which surface has the low-E coating by holding a cigarette lighter flame near one of the panes and looking at the four reflections (one for each surface of the two panes). The coated surface will have a bluish color, while the other three flame reflections will be orange, like the flame itself.

And yes, ther is a lot of Mumbo-Jumbo in the window business. As for a particular manufacturer's marketing claims, they are most likely a result of laboratory testing (done a lot of that) on complete windos assemblies, frams, sash, hardware, and glass. The window frame and sash will skew the values one might get measuring only at the center of a window pane. The worst part of any window, from an energy standpoint, is the perimeter of the insulating glass panels, where aluminum tubes are used to separate the two glass panes.

Have Fun, Moby Nick

[N. Scheuer]

Correction to paragraph four, above:

-----or on the inside of the exterior pane, so that heat from outside (imagine a hot asphalt parking lot beside the building) can be reflected before it is able - - - -

Sorry, Moby Nick