Dana-
 
We use UV Plexi in our 200 year-old historic house, but we never open the
windows.  We drilled through the plexi and attached it right into the sashes
with screws.  The plexi has been in place for 5 years or more with no
yellowing.  If your windows are on the right type of sashes I suppose that you
can mount the plexi to the sashes and still be able to open the windows.  The
house curator recently acquired a UV meter and checked the levels, and she was
very happy with the readings.  We've had essentially no damage to the furniture
and textiles that are on permanent display throughout the house.  If you want,
I can get the information on the brand that we use.
 
Leslie Johnston
Historic New Orleans Collection
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