Longevity of window films in triple pane IGUs?
https://buildingscience.com/sites/default/files/migrate/pdf/PA_Foam_Shrinks_FHB.pdf
In this FHB article, Lstiburek writes:
“Window film is a poor substitute for the right glazing at the time of the deep-energy retrofit, we used the best windows we could buy: triple- glazed heat mirror windows from Hurd. The third layer of glazing is a film suspend- ed between the two layers of glass. The per- formance was pretty good, but the longevity of the inner layer of film was not so great. After 16 years, I can see fish eyes on the film—not enough to make me want to replace the windows, but enough to keep me from specify- ing window film in the future.”
I understand that companies like Alpen (and maybe others?) have moved towards films for the middle layer in their IGUs.
Can anyone comment on if they have experienced these same fish eyes recently?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Alpen has been offering Heat Mirror, or suspended film IGU's for as long as they have been in existence. It's not that they are moving toward film as the center lite of their IGU's, rather they are now offering products that don't use suspended film for the center panes.
Alpen has always been reasonably successful at avoiding the problems with suspended film technology that plagued pretty much everyone else who has ever offered the product, but apparently they decided some years back to look into offering different options to their customers in addition to their suspended film products.
While energy performance of a single suspended film in a triple pane configuration is no better than a more traditional triple pane, the potential advantage of using either suspended film or thin glass is reduced weight and the option of offering two, three, or even more layers of the film between the two outer lites while maintaining manageable weight and thickness of the IGU.
I don't know of any other window companies who offer suspended film as a primary product, but there might be a few regional or local companies around who do so.
Friends of mine bought a house built in the 1980s that had a lot of high-performance details for that time, including windows with a suspended film in the middle. I'm not sure of the brand but many of the films have cracked, approximately half of all of the many windows. The windows are at or beyond the end of their lifespan anyway; I'm not sure when the films cracked. From what I understand, Heat Mirror had a lot of failures in that era but they were mostly or entirely solved by 2000 or so. All-glass triple glazing is very heavy so I have no problem with Heat Mirror in a contemporary window.