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Cardinal glass i81 coating on double-pane vs. triple-pane

TjHhLpRXCC | Posted in Energy Efficiency and Durability on

We are building a new house and had planned to use triple-pane glass in extruded fiberglass/composite frames. In particular we have one large picture window 96″W x 72″H. Just found out from window provider that they cannot (will not?) do this window as triple-pane due to size….particularly the weight of the glass. He suggested alternative of double-pane using new Cardinal i81 coating which he (and Cardinal website) claims achieves nearly the same thermal efficiency as triple-pane (thermal efficiency was major reason for using triple-panes). Does anyone have an opinion on this alternative?
Thanks in advance!

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  1. Danny Kelly | | #1

    From what I know, Cardinal LowE-181 is for passive solar homes for south facing windows - has a high SHGC. Not sure of your climate zone or what you are trying to accomplish, but does not sound like a good substitute with the little information provided.

  2. HyvL3Cak9C | | #2

    Have you seen "Serious Windows". These utilize a suspended "film" (or films) instead of another pane of glass and would solve the weight problem. You can contact me at [email protected] for more information.

  3. TjHhLpRXCC | | #3

    Tom and Danny -
    Thank you both for your quick responses....

    Danny - I'm not sure but what you mentioned may be the Cardinal LowE-180 glass and not what they're calling their i81 coating (note the "i" at the beginning and not a numeric "1"). I haven't seen anything on the Cardinal website talking about the i81 coating being high-SHGC, etc...their main selling point seems to be heat retention with the i81 coating.

    Tom - we have done a token amount of research on the "film" you mentioned....I believe it's called a "heat mirror" and is actually another Cardinal glass option (I believe Serious Windows gets their IG units from Cardinal) We have seen various reports/reviews where people have indicated this "film" layer has issues with failures and so we're a bit "scared" of putting in IG's with this.

    A few more specifics about our requirements: home location in eastern Nebraska...southern edge of the "northern" climate zone for Energy Star, etc; walk-out ranch on a lakefront lot; probably 75% of the glass is on the back of the house to maximize views of lake; back of house faces almost due north and will therefore be exposed to very cold northern winds; U-values being weighed much heavier than SHGC due to northern exposure of majority of glass.

  4. davidmeiland | | #4

    What type of performance do you need? What specs were you looking at with the triple pane units? Here's the chart from Cardinal's site, and it looks like you can get a good U-factor with either high or low solar gain. Do you have any price quotes yet?

  5. TjHhLpRXCC | | #5

    David -
    We are looking for U-factor of .20, which it appears from the chart we can get using any of the Cardinal glass options with the exception of the LowE-180 if we use the LowE-i81 coating and the Argon gas fill. We are waiting on prices for these glass options from our supplier. Thanks for posting the chart...we had seen this on the Cardinal website and the numbers quoted look good to us and that's why we're looking for opinions from others as to whether there are any known issues with the LowE-i81 coating, it REALLY a viable option vs. triple-pane?

  6. user-954346 | | #6

    Dave, The chart from cardinal is providing "glazing only" numbers not whole window frame installed! So I think you will see that once glass is in a frame the values will decrease in performance to where triple glazed units may be more comfortable especially the 1 and 3/8" thick IGUs from Canada and Europe. Does anyone else know?

  7. gusfhb | | #7

    I don't believe you will ever regret getting better windows

    Find a new window company if this one will not do what you want.

    Try contacting Cardinal and asking who will install their thicker igu's

    Have a frame made up, as I had suggested on a different thread.

    Don't let your vendors make you decisions

    I am installing 160 sq ft of triple pane cardinal with i81 right now, I will let you know how they work out

  8. GBA Editor
    Martin Holladay | | #8

    Instead of one very large fixed window, consider installing two smaller side-by-side fixed windows (ganged windows). You may be able to fill the rough opening with two fixed triple-glazed units instead of one huge double-glazed unit.

    A triple-glazed IGU with double low-e coatings and argon or krypton is obviously going to have a lower U-factor than a double-glazed IGU. That means it will be more comfortable on winter nights. Of course, a double-glazed window may have a higher SHGC; for some south-facing windows, it may be reasonable to choose the glazing with a higher SHGC in spite of its higher U-factor.

  9. wjrobinson | | #9

    There was an interesting post back awhile that said some study showed that even certain rated north facing windows could be net gainers of heat if so desired.

    Link to that discussion ?

    Martin, looks like Dave's main concern is for specs for his north "view" Windows. I run into the same issue here with so many homes built with lake views verses solar siting rules.

  10. GBA Editor
    Martin Holladay | | #10

    It sounds like you are referring to this article: Windows That Perform Better Than Walls.

  11. gusfhb | | #11

    I personally take with a grain of salt any talk of net gain. I love passive solar, but if glass in all directions was a net gainer, we would all live in greenhouses. I also think that real south solar gain is usually overestimated. annualized gains look great on paper, but sitting next to a 45 degree window pane on a cold winter night is the reason why I am doing some of the things I am doing.

    yeah, if this is a view window[IOW not south facing], I am going to call it oversized. Odds are you will get the same view with a window half the size. Again another reference from 'From the Ground Up'
    run some sightlines and you will quickly learn that you can make the windows smaller without really affecting the view.

  12. TjHhLpRXCC | | #12

    Thanks to everyone for your responses...the information is very helpful! At this point we are 99% sure we are going to go with smaller windows installed either as one unit with mullions (we're assuming that's what Martin meant by "ganged") or possibly installed as separate windows with a dual 2x6 vertical support between them (for structural strength). This will allow us to retain the triple-pane glass while minimally impacting the "view" out of the window(s). One advantage of installing them as separate windows is that we should also be able to reduce/simplify the framing requirements for the window headers...

  13. oberon476 | | #13


    Who is the vendor? There may technical reasons why they can't do a triple pane at that size while they can do smaller triples or duals at that size, but weight of a fixed unit is one that I would definitely not consider insurmountable.

    Assuming (total guess) that they would be using an IGU with a glass make up of 3.9mm / 3.1mm / 3.9mm, total weight of the glass would be right about 270lbs - heavy but not a deal breaker. I would push them a bit, but keep in mind that if this isn't a standard offering, then be prepared for sticker shock.

    Serious Window suspended film IG's are not fabricated by Cardinal. While Serious does use at least some Cardinal coated glass, they manufacture their own IGU's.

    Good call on the difference between I81 and LoE-180, the numerical similarities can be confusing.

    While I81 is technically a "softcoat", meaning that it is applied in a sputter application, it is a durable softcoat that is intended to be used for surface 4 applications. I81 doesn't use silver in the coating so it can be exposed without risk of tarnishing like silver-based softcoats, and the top layer of the coating is very scratch resistant as well - therefore durable and surface 4.

    LoE-180 is a single-silver high solar gain softcoat that has to be fabricated to the interior of an IGU or else it is going to deteriorate. And a bit off-topic, the chart posted earlier is not the best indicator of "normal" LoE-180 performance.

    LoE-180 is intended to be a surface 3 coating. Since the technology to sputter 180 on surface 3 and I81 on surface 4 (dual pane) doesn't currently exist, the chart shows 180 on surface 2 and I81 on surface 4 - not optimum for HSG applications - in the dual pane. Triple IGU performance numbers listed, no matter the specific coating, are based on coatings on surface 2, 4, and 6 - which also means that the glass (at least the center pane) in those make-ups has to be heat strengthened to avoid breakage due to thermal stress.

    And at risk of getting even more off subject, while I81 is not intended to be a "stand-alone" coating, using it on either a single pane, or on surface 4 of a dual pane (without a second coating), will result in energy performance numbers comparable to a typical hardcoat.

    In a 3mm single pane application, I81 has a SHGC of .69 and winter U-value of .63. In a 3mm glass surface 4 dual pane application, SHGC of .67 and winter U-value of .36.

    And back on subject, I personally like Martin' suggestion of breaking the big window into two smaller ones (pun intended, sorry), but if you really want the large expanse of uninterrupted glass, I would tell the vendor that if they don't want to manufacture the triple (can't might be the issue), then there must be someone who will. Cardinal can fabricate triple IGU's that size (and larger), but again - potentially EXPENSIVE - so the ball is really in the window manufacturers court. And while there really may be technical reasons why they can't go that big (I can think of a few right off), find out if it is reluctance or truly not possible for them.

    Good luck!


  14. TjHhLpRXCC | | #14

    Thanks for the detailed information. While not even PRETENDING to understand the "why's" behind his numbers, our window supplier said that for a 96Wx72H window they would have to use 1/4" glass and that the glass manufacturer told him it would have to be tempered to reduce the risk of breakage. His calculations put the weight of the IGU at a whopping 486 pounds and he said that for them that would just involve too much risk and liability. He also pointed out that with the 1/4" glass they would not be able to get the proper air spaces for the argon/krypton gas to work efficiently.

    Based on the above and the need to keep things moving forward, we are planning to go the route of a pair of smaller windows to fill the same opening. (There is still a slight chance we may go with the i81 coating on a double-pane but that will depend on the cost and the whole window energy rating calculation....) It's not the end of the world for us to split the one window into separates...we also have an opening in another location of the house that was originally planned as a 132"W x 60"H that we have split into multiples for many of the same reasons/problems with this 96"W window...alas, building projects are a battle of "wants" vs. "cans" vs. "can affords"....

    Thanks again to everyone for their input!

  15. TjHhLpRXCC | | #15

    One additional question for everyone (still not giving up hope for being able to have one big window).....does anyone have any suggestions about manufacturers (frame and/or glass) that they think would be able to produce this 96"Wx72"H (8'x6') window in triple-pane? What about a window that is 132"Wx60"H (11'x5') in triple-pane??

  16. davidmeiland | | #16

    LoE-180 is intended to be a surface 3 coating. Since the technology to sputter 180 on surface 3 and I81 on surface 4 (dual pane) doesn't currently exist, the chart shows 180 on surface 2 and I81 on surface 4 - not optimum for HSG applications - in the dual pane.

    Couple of questions here. The chart shows 270, 272, and 366 in combination with i81 in dual pane IGUs. Does that mean that those three coatings can be put on surface 3, with i81 on 4? Or, does that chart assume that all of the inner coatings would be on surface 2? And... what are the performance differences between 180 on surface 2 vs. surface 3? In another thread (on JLC) I came away with the impression that the differences were minor.

  17. gusfhb | | #17

    3 coatings on triple pane, not double

    Two smaller lites would technically have poorer thermal performance than on larger lite. more edge of glass and frame per square foot.

    I would not normally give anyone a hard time over amount of glass, those who live in glass houses etc, but that is a lot of north facing glass.

    Think about a few things regarding view. Any window below 3 feet from the floor is going to have a nice view of the deck rail[which you probably have on the lake side] not the lake. Any glass higher than your eyeball is likewise not giving you a view of the lake[perhaps mountains. The real money saver is going to be reducing the total glass area, which you can probably do without reducing the view.

  18. TjHhLpRXCC | | #18

    Keith -
    I understand what you're talking about re: the tops and bottoms of the windows and the actual "view" that is gained by raising/lowering them. We have used a modeling tool (called "Sweet Home 3D") in laying out the floor plan of this house and have tried various configs for the windows, etc....the 8'W x 6'H window could be shortened to 8' x 5' but we like the way the taller window opens up the room a lot more even though technically all we're adding to the view is more of the sky. (As an aside...the modeling tool I mentioned is available as a free download from and is very easy to use in laying out rooms, doors, windows, has been a tremendous help to us!)

  19. oberon476 | | #19

    Dave, Looks like I was still typing while you were posting...

    In reply, and first, the calculated weight in my post was based on using 3.9mm (5/32") tempered glass in the opening. I need to revise the weight because while you can use 3.9mm glass at 96", Cardinal does have a 3.9mm glass maximum size of 30 ft² - and since your window would be 48ft², 3.9mm would be too thin to be used at 96x72.

    A 48 ft² window could be fabricated using 4.7mm (3/16") tempered glass rather than 1/4" that the window rep stated (1/4" would actually be 5.7mm or closer to 7/32" - probably splitting hairs at this point), 4.7mm does fit Cardinal spec for that size IG - but it would be pushing 350lbs for glass alone which once again is not insurmountable, but it would cost a fortune and it does sound like the window company is adamant about not wanting to deal with a unit of that size and depth. I am truly sorry for any confusion I caused with my earlier post on the glass thickness issue....apparently I had a total brain cramp at the time.

    At the sizes you are considering for single windows you might have to consider light commercial windows and that could result in using aluminum frames (among other changes), something that you do not want to do in your environment. There are always alternatives, but breaking it up into multiple mulled units really seems like the best idea.

    If you decide on triple pane versus dual pane you would then have the option of coating surface 2 and 5 (and combination of 270, 272, 366, or even 180 in pretty much any combination - but no I81), or you would have the option of coating three surfaces - 2, 4, and 6 once again using either 270, 272, 366 on surfaces 2 and 4, and then I81 on surface 6.

    If you coat surfaces 2 and 4 then the glass (at minimum the center lite) would have to be heat strengthened in order to avoid thermal breakage. The three coatings versus two would improve the U-value, but heat strengthening would also add cost to the unit in addition to the added cost of the third coating.

    David, I only mentioned 180 in my reply because 180 is intended to be used as a surface 3 coating for maximum solar heat gain while still supplying a pretty good U value. Putting 180 on surface 2 and I81 on surface 4 just doesn't make sense in my opinion since you lose SHG advantage and end up with a U value less than you would get using a more appropriate coating on surface 2.

    The other coatings that you mentioned in your post are designed as surface 2 coatings so the addition of I81 on surface 4 would not require back-to-back (surface 3/4) coating. It is not currently possible to coat surface 3 with any LoE and then surface 4 with I81.

    Consider that using 180 as a surface 3 coating results in SHGC of .69 and VT of .80. In the chart listed earlier, using 180 in conjunction with I81 the glass has a SHGC of .59 and VT of .71.

    Taking into account that the I81 plays some part in the lowering of both SHGC and VT, I would suggest that the majority of solar heat gain loss is related to surface 2 versus surface 3 application. Lower solar heat gain using LoE-180 on surface 2 versus surface 3 is noticeable and it is enough that Cardinal does advise that it should be used as a surface 3 coating for maximum solar heat gain . The difference in U-value when deciding between surface 2 and 3 is negligible.


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