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?
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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.
Thanks for that correction about Alpen. I believe Litezone touts multiple layers of suspended films like you mentioned, but there's very little in the way of example builds using them, and some interesting google reviews of the company.
Litezone does offer suspended film technology as well, but they only build IGU's and are not a window company.
They do have a few window companies, something I should have remembered when I replied, that offer their product but you need to look on their website for details.
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.
Andy,
The internet is a terrible dustbin that never gets emptied. You will find horror stories about heat film windows that could lead one to think the technology is inherently bad. The early 80-90's Hurd and Sun-something windows did have numerous failures which generated a lot of bad reviews that still persist on the web. Similar issues involving the Serious windows brand have added to the trail of tears dished up in searches. Much of the horror stuff dates prior to 2000 like Michael says, so check the dates on what you see.
I will note that the only way I can perceive my Alpen film's presence is by wearing polarized sunglasses indoors. You will see a sort of dichroic effect that of course is not visible under normal conditions. I would guess that a quad unit (two films) might be even more dramatic.
As an admitted Alpen fanboy with 41 single film units total (plus three doors with Alpen glass) I am very happy with them all nine years on from original installation. I may be tempting the gods by saying that all are perfect, but I can recommend them as excellent performers both thermally and for air leakage. At 8,000 ft on a ridge we do get some fierce winds. All the windows are fiberglass profiles, which have handled the temperature extremes quite well.
If you are building at an altitude over 5000 feet, be aware that many brands of windows may offer triple glazing, but NOT with argon gas installed for windows above that altitude (or even lower). This limit includes the trip to your location, so check the shipping paths. The hit on performance by only having normal air is significant. Alpen may be the only manufacturer that ships to high altitudes with argon thanks to the argon bladders they use to equalize differences in the IGU/atmosphere during the trip up or down to the final elevation. Not having this feature can result in some fun house mirror effects on sealed units shipped to elevations different from the factory's.
The newest (3-4 yrs) offering from Alpen incorporates very thin glass as the middle layer and by the specs, better performance. I believe the glass is related to the very thin glass used in LCD TVs. I would guess that they do not weigh as much per unit as a three full thickness glass unit might, but Alpen can provide that info. I have heard Alpen is/has expanded into a new factory space, so they must be doing something right.
Greg Novak (aka Oberon) talks about thin glass in this excellent article: https://www.greenbuildingadvisor.com/article/what-to-know-about-tempered-glass.