Double-pane in the butt windows

failedseals4Is it just me, or is anyone else sick of seeing failed window seals and the apparent inability of these seals to last more than 20 years? In some cases I am seeing whole developments of houses with windows failing as early as 12 to 15 years due to failure of a particular type of spacer between the two panes of glass.

failed-seal1If the purported energy savings of double pane windows is difficult to defend, it certainly does not pencil out if those windows have to be replaced every 20 years–even if it is only the glass part. Generally speaking, when replacing your windows, they will almost never save you in energy costs, amortized over the number of years the sales person would like you to believe, what the replacement and installation costs of the new windows will be. This of course can vary with energy costs and location and other factors, but generally speaking this is true in relatively moderate climates like Seattle.

failedseals3I think it may be time to rethink the whole notion of double pane glass, sealed units–or units that have special gasses installed in them that increases their efficiency, cost and failure rate.

Surely it costs money and consumes resources to make glass. There are houses a couple of hundred years old with original single pane glass that suffer from the poor condition of wood sashes and exposure—but not from failure of the glass. Glass is pretty dang durable stuff—and it is VERY cheap, being made out of one of the most abundant resources on the planet.

Why not go back to window installations, more like the storm window approach?

failedseal2Several manufacturers’ of windows have, in the past, made (and still do in at least one case—Pella) windows with a removable panel. These windows were quite efficient and easily repaired if damaged. If a kid kicks a soccer ball through a sealed unit window, and only breaks one pane, the entire glass unit must be replaced. If it was a removable panel type window only one glass pane might have to be replaced and thereby having a less serious impact on the kid’s allowance.

The failed seal issue, though, is what really gets me. There are no failed seals in windows with removable panels. These windows could theoretically (sans the occasional soccer ball) last indefinitely and contribute to huge savings in energy and the use of natural resources over the lifetime of the house–or even in reuse beyond the life of the house.

I think it is false economy to think that sealed glass units are saving tremendous amounts of energy over what removable panel windows would save. The more complicated these windows get, with the fancy gases and the triple panes, the more difficult it becomes to justify the costs. It seems that any small amount of supposed savings, that could theoretically be gleaned, could be more than offset by focusing more on whole building air leakage, better use of insulation and slightly smaller windows—not to mention more careful planning of window location. Just not having every window in the house an opening type window would represent a huge savings. They should open where necessary for egress and ventilation. Most houses have many windows that never need to be opened and never get opened—so why are they openable type?.

Another thing that could be done with removable pane windows is that one could have a changeable panel that would allow for reflective coatings in the summer and no coatings in the winter. This would allow for the home to benefit from more solar gain when desired. Windows with reflective coatings can actually increase the heating needs of houses in cold climates by limiting solar gain the same way no coatings increases cooling loads in the summer.

Removable panel windows could also be fitted with insulating blinds that could be used to recoup any supposed reduction in efficiency between the two types. Regardless the arguments, over the long-term life of the house, it seems unlikely there would be any meaningful energy savings by choosing sealed units over removable panel units.

We are fighting over miniscule relative increases in R-value between the double pane windows and the most expensive triple pane windows full of “hot-air” gases. It is better in my opinion to spend money in more productive ways, until someone smarter than me invents High-R Glass–that one can still see through, let’s light in and automatically polarizes itself by season.

It seems that we are making expensive choices to save a few dollars when those same dollars could be spent in ways that could actually provide more long term energy and resources savings.

There will never be a perfect solution as long as we want to get in and out of our boxes, breath in our boxes and have natural light in our boxes. The question becomes one of where to spend our money on offsetting all the compromises.


By Charles Buell, Real Estate Inspections in Seattle

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  1. Interesting article, I just bought a house built in 1980 with double pane aluminum windows, half the windows have at least one failed seal.

    Some of them barely physically seal the outside from the inside judging by the amount of cold air that leaks in and the smell of smoke from a neighbors wood stove somewhere near by, so I got a roll of masking tape and taped around the edges of the window frames in the bedrooms at least.

    Then I got to thinking about replacing the windows vs replacing the energy guzzling electric furnace with a heat pump.. Even before seeing this article about windows, I had decided the 35 year old electric furnace would be first to go as a heat pump would save more than new windows ever could.. With that in mind, is there a cheaper “less efficient” option for windows, one thing I do like about double pane windows is the noise reduction from outside, even then I’m inclined to think that replacing the original windows in the house with their failed seals and leaks would probably never be worth it in the end – I’d never make the money back in saved heating costs..?

    • Charles Buell says

      “Payback” is relative to where you live—how severe your weather conditions are but generally no—they won’t—especially since your windows are already double pane. The air leakage is a bigger concern in my opinion. Look at seeing if you can find some with a removable pane when you replace them.

  2. Charles,
    I can agree with that window failure is a big problem and I see it consistently. There are many reasons for these failures, from poor installation, poor construction of the window, to inferior materials. Primarily, the source of these failures is at the seal. Typically the seals around the glazing units are made of butyl, petrol-chemical product. Overtime, (and yes 15 to 20 years seems to be it’s limit) butyl will dry out, losing it’s flexibility. Once this happens the gasket is susceptible to cracks and fissures. This is is usually coupled with a frame made of dissimilar material such as vinyl which expands and contracts at a different rate than glass. With the glazing unit siliconed to the frame, expansion and contraction of the frame adds stress to the seal, causing it to fail.
    What I can’t agree with is the idea that we throw out the idea of a more efficient window. An efficient window is central to creating a properly performing building envelope. At 15% glazing to floor ratio a U .30 (R-3) window will reduce the effective R-value of a R-50 wall to R-15. Simply, by replacing the windows with a U .15 (R-6.66) would bring the effective R-value of the wall assembly to R-37. It just simply is not true that we are chasing insignificant increases in R-value. It is not possible to separate windows from the rest of building in terms of the overall performance of that building. A more systematic approach should be taken.

    • Charles Buell says

      Mark, well since this is my blog I get to say hooey 🙂 The notion that windows cannot be constructed that can equal sealed pane windows is absurd—we just do not have the political will to do it. The infrastructure invested in going the other direction is too entrenched. It can shift as people wake up and smell the roses and other alternatives are provided—which is starting. We can push u-values and r-values in all kinds of directions but the bottom line is that double pane windows and then triple pane windows with all the fancy reflective coatings and inert gases will never pay for themselves and actually end up consuming more resources when they have to be replaced and/or built. I totally disagree with the concept of “wall effective” r-values. Air leakage is a far bigger factor in this than whether the window is r-2 or r-3. The notion that there is any such thing as an cost effective, readily available, “green” r-6.66 window is science fiction. What I am recommending is and always has been a “systematic approach” to energy efficiency and have been doing so since 1971. There are way more effective ways to accomplish these goals than continually chasing microscopic increases in window r-values.

  3. I appreciate your opinion on spending money in different areas that will provide a more long term energy and resource savings. There are so many different ways to be energy efficient and save money. In the mean time I hope someone does invent a better High R Glass. Thanks for sharing.

  4. Elwyn L Jordan II says

    I bought an house in 1988 in Richmond VA that had beautiful wooden frame single pane windows. The house had ugly aluminum framed storm windows. After two years I removed the storm windows. I could not detect any significant change in the electric bill. After about to years I paid about $1200.00 to have the window putty replaced. I sold that house in 2011 and moved to newer neighborhood, all of the houses there have contractor grade (cheap) double pane windows. Three were replaced by the seller before closing and I have replaced five since for close to $2000. The windows are falling apart. I thind double paned windows are a SCAM. I am faced with a huge expense if I sell this house.

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