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Re: GBlist: window longevity
A few thoughts on the window durability thread:
Terry mentioned the old Andersen windows that had welded-glass-edge
insulated glass units (IGUs). I feel that the industry lost a great deal
when PPG and LOF abandonded that technology. A few years ago I did some
work for a guy who was considering purchasing the last working
welded-glass-edge IGU factory--one in Ohio owned by LOF--and that gave me
some insight into the advantages of that technology.
The basic idea was (is) that instead of relying on organic seals between
two layers of glass and the metal spacer, the edges of the glass are
"welded" together. This seal is much tighter and less prone to failure--as
Terry and others who have worked with 30- or 40-year old Andersen windows
with this type of IGU can attest. They are also much better at containing
the low-conductivity gas fill. The problem with welded-glass-edge IGUs came
about when Andersen decided it wanted to go to a thicker air space to
provide improved energy performance. Cardinal did that quite easily with
their IGUs and took market share away from PPG and LOF. These two companies
invested millions trying to make welded-glass-edge windows work with
thicker spacings. At the end, LOF was using their Energy Advantage low-e
glass and putting carbon dioxide in the IGUs (which is similar to argon in
energy performance but not used with organic seals because it is difficult
The problem was that the thicker the space, the greater the forces on the
IGU edges when large differences in temperature occur across the window.
Unacceptable edge failures occurred when they went to a 1/2" or 5/8"
spacing to match Andersen's requirements. The irony to this long-winded
story is that an ideal solution might have been to go back to a 1/4"
spacing, which worked very well for decades, and put krypton in the space.
With krypton the ideal spacing is much narrower than it is for air or
argon, and the energy performance is far better than the other gases used.
The person I helped write a business plan for ended up getting cold feet,
and as far as I know, the last welded-glass-edge factory was torn down.
This was a real loss both for the window industry, which lost a product
they had been able to really stand behind, and for the building industry,
which lost a product we could depend on.
Alex Wilson, Editor & Publisher
Environmental Building News
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