Choosing Triple-Pane IGUs
Help me pick triple pane IGU to help combat solar glare, and patio heating
What should I be looking for in the specs of the many different IGU options to help reduce glare without significantly reducing visible transmission?
Background: New construction, NW Montana, main living areas face West towards a body of water. I do have large overhangs (20′ and 22′) to help control solar gain and glare that way. However, the sun reflects off the water which is extremely hard on the eyes and the the overhangs don’t help this at all. The windows and doors are coming from Europe and I can pick whatever glass I want. I have been leaning toward Guardians SNX 70 which is their top-of-the-line triple silver low e-coating with the highest light-to-solar gain ratio I have seen. I want high visible transmission because the majority of the year is not super sunny and beautiful and I want as much daylight in the house as possible. I recently upgraded my current house from Cardinal’s 272 on the west side to 366 and 340. The 340 is noticeably better at controlling glare but it is also noticeably darker. Is there just no way around it? 366 is better at glare than 272 and only marginally darker visibly, so there must be another “spec” that is playing a role.
I attached screenshots of the SNX70 on “ExtraClear” and “UltraClear” glass, as well as SN70/35 on ExtraClear. As you can see the basic numbers of VT, SHGC, and U factor are all similar, but the various reflectance numbers are different. These specs are from Guardian’s CE website and analyzed in NFRC ratings. Saint Gobain has their own line of coatings but they seem pretty much the same.
Secondarily, what measure best translates to exterior heating on the West side? My sister just finished a new house which used Cardinal’s 366 on the west side. They also have a patio on that side and the patio surfaces heat up A LOT more under the windows than they do elsewhere. To the point of rendering their patio dangerously hot on certain days. As you can see there’s a ~10% difference in solar reflectance between regular glass and low iron glass. Seems to me the low iron glass option might heat up the patio even more than regular glass?
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Replies
I'm not aware of stock coatings that would limit glare while not affective visible transmission. Generally speaking, you want VT to be .40 or higher, though that number includes the frame area so it depends to some degree on the window.
A polarizing filter would reduce glare without significantly affecting VT; there might be after-market films you could apply, though they might affect window warranties.
Thinking you’re right, but thought I’d throw it out there!
Generally for reflected glare you want a vertical polarizing filter. These cut 50% of the light, so maybe not something you want but do make a difference.
Otherwise you want lower VT which is the opposite of the goal in your case. Some motorized shades might be the better solution for those couple of hours in the afternoon.
Yeah I think you’re right. Shades are absolutely necessary.
If you haven't came across it yet, Cardinal has a technical guide with some fairly detailed information about their coatings. I haven't seen the same from other manufacturers, but I found the information in it useful and mostly generally applicable. https://www.cardinalcorp.com/technology/reference/technical-glass-guide/
That’s an awesome technical guide they put out. I don’t see any mention of glare, but it’s a handy resource nonetheless.