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GBlist: R-20 windows and other (possible) wastes



Returning to an old  thread I would agree with Chris Mathis that the
world could probably survive without an R-20 window.
It would probably be useful in the sense that we could forego any
considerations of placement and function in a whole house design but
then we would be that much further removed from knowing where we fit in
the order of things.

All of Chris's concerns seem relevant and I would add my own basic
concern that advancements in insulative properties would not address the
limitations of the basic design i.e.. edge seal and seal failure. Terry
just gave some statistics on failure rates from 1995 on 15 year usage. I
was in a 25 year old house in the northeast recently that had 8 of 30
units fail. An attached 15 year old sunroom will Pella windows had 3 of
15 units fail. 

Generally when units begin to fail the owner will opt for either total
replacement of the glass in all units (this is what seems the most cost
effective approach if there is a fear of all the units failing)or (when
looking at the cost and considering the 'age' of the windows) will often
replace the entire units. Replacement of glass alone can easily run
$10-15,000 which in the worst case scenario is $1000 per year of usage
(not a figure you would want to use in calculating energy savings)

Another aspect of glass usage is the difficulty of recycling (i.e.
separating) glass from sealed units.

Aside from the glass units themselves if you look at most of the basic
designs for setting and sealing the glass into the units you will find
some component that in failing will compromise the life of the glass -
most commonly the setting blocks or exterior seal. Ironically the units
in which the glass is easiest to replace lack a good exterior seal.

My ideal window is one whose real cost justifies its energy savings. A
lot of the market usage of technological innovations seems dedicated
more to attracting consumers than benefiting the environment. Like Terry
said I think I'm going to take another look at air vented designs. 

John Salmen
TERRAIN E.D.S.
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