Pella Impervia Window Glass UV Protection
I have 5-yr old Pella Impervia windows. With the recent Arctic-like weather in the mid-west, I left my window coverings open to maximize passive solar heat. I can feel the heat near the windows. Also noticed that my photo-chromatic (Transitions) eyeglasses go full dark near the SE facing windows. They do not go dark in a car due to the type of UV filtering in car glass.
At the link, below, Pella advertises great (but non-specific) UV protection in the Impervia glass. I seem to recall specific info but can’t find it now, i.e., blocks xx% UV-A and/or yy% UV-B.
https://www.pellabranch.com/windows-doors/energy-efficiency/what-is-low-e-glass/
Specs seem to vary for individual windows/doors. The following two paragraphs are examples from my invoice:
Glass: Insulated Low-E Advanced Low-E Insulating Glass Argon Non High Altitude
Performance Information: U-Factor 0.27, SHGC 0.33, VLT 0.62, CPD PEL-N-127-02234-00003, Performance Class CW, PG 45, Calculated Positive DP
Rating 45, Calculated Negative DP Rating 45, Year Rated 08
From 4-glass panel sliding door:
Performance Information: U-Factor 0.29, SHGC 0.27, VLT 0.51, CPD PEL-N-230-00014-00001, Performance Class R, PG 20, Calculated Positive DP
Rating 20, Calculated Negative DP Rating 20, Year Rated 08|11
If I have great UV protection, why are the eyeglasses going to full dark? Will the UV damage oriental carpets on the floor and art on the walls?
Usually, when not so cold, I use Hunter Douglas light filtering Designer Screen shades that supposedly block 95% of light. I am satisfied with them and use when necessary to block sunlight. The nice thing about them is you can still see what’s outside to a limited degree.
Seems like I’m in a spot between energy efficiency and sun damage to valuables. Any thoughts? Thanks.
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Replies
As you already noted, your photochromic glasses go dark near your windows but not in your car.
Windshields in cars are made of laminated glass that blocks up to 99% of UV rays, while the windows in your home are protected from UV using a LowE coating on the glass.
While I couldn't find your specific window or door CPD numbers on the NFRC website, other products within the same CPD categories (PEL-N-127 and PEL-N-230) used Cardinal LoE-270 which blocks about 86% of UV from passing through the glass.
You also need to keep in mind that visible light is also responsible for fading and damage along with UV and you need to protect your light-sensitive belongings from both UV and visible light to prevent problems.
This is an interesting topic that doesn’t get much discussion on GBA. I’ve read so many blogs and Q&A posts here over the years discussing the merits of passive solar, how super-insulated won the war, avoiding east and west facing windows due for risk of overheating, etc.
But never any consideration, at least no mention, of concern of UV and visible light damage to furnishings, artwork and other valuables.
I really hope this question attracts some more responses; I’d like to hear how other long-time contributors handle these concerns. Maybe this should go to Kiley for a future blog post idea?
Thanks everyone,
Aaron