Have glazing films improved from those on the market 20 years ago?
GBA Editor
| Posted in Green Products and Materials on
Manufacturers such as Serious Windows use films to separate “air” spaces in the triple and quadruple glazed units. Their commercial warranty on these units is 10 years and their residential warranties are lifetime of original owner. Is there good evidence that the films will stand up for the 20 years which most sealed units are warranted?
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Replies
Jeffrey,
That's the question a lot of us are wondering. According to Southwall Technologies, manufacturer of Heat Mirror glazing, early problems have all been overcome, and the latest versions of the glazing are problem-free.
Time will tell.
All plastics have a limited lifespan, particularly when exposed to UV. Their main advantage in windows is their light weight compared to additional glazing layers. But plastic will never last as long as glass (as long as the kids don't play baseball nearby).
New windows should be designed so that if the spacer or the films fail, the glazing can easily be replaced.
Martin, Robert and Doug -
Thanks for your responses. I realize that glazing can be replaced and that plastic may not last as long as glass, but my question relates to the relative longevity of the sealed units. If most manufacturers are willing to warranty their products for 20 years, I assume that the sealed units will (mostly) last that long. If the films either cause the seals to fail or if the films themselves break down making them less transparent or allowing the air spaces to stop working as they are designed, then the cost savings in energy saved and the energy savings in embedded energy are not true savings. As an architect, recommending energy efficient building envelopes to clients who want to save both energy and money, I am not inclined to recommend sealed units that will require replacement in a few years. If, however, they can last at least as long as their all-glass counterparts and can provide better U-value and air sealing performance, then I'd be inclined to use them on my projects. I have heard that accelerated testing has always caused failure of the films, but I have not seen these test results.
Thoughts?
Another issue to consider is the balance of heat loss vs solar heat gain. The balance, in my estimation, has shifted much too far toward insulative value, ignoring the potential for a net energy gain during the heating season in a cold climate - even in cloudy Vermont.
Passive solar gain - the only truly green heat - requires minimizing the obstruction between Old Sol and our inner landscapes. A high solar heat gain double glazed, lowE, argon-filled window with non-conductive frame and thermal break in the glazing unit often offers the most net gain - and at the lowest cost. But, of course, it also requires integrated design, with proper orientation, open floor plan, sufficient and appropriately-placed thermal mass, and well-designed overhangs for summer shading.
Not only is there little incentive for passive solar design (e.g. federal window tax credits that require low SHGC glazing nationwhide), but it seems that few architects are interested or willing to compromise aesthetic sensibility for straightforward functionality - no matter how green.