windows and new energy codes

lori_inthenw_gwAugust 13, 2013

Well, I've had to learn more about windows and glazing lately than I ever really wanted to know! Would like more opinions, though-- esp. from those not trying to sell me anything.

The basics: new construction, energy code requires average U value to be no more than 0.3. We are aiming for low maintenance, so selected fiberglass and wanted black inside and out, so chose Milgard. So far so good. Then it's time to do the weighted average to calculate the U.

We'd like some thermal gain since we live in a cool climate and A/C is not an issue. But the glazing that has better solar heat gain coefficient has worse U values and vice versa. The person we've been working with at the window dealer said we would not be happy with 366 in rooms that also had 270 or 180 because we'd see the difference, and that it looks greenish from the outside. She also advised against the triple panes we had included, because "they'd be reflective from the inside and you see a bunch of triple reflections" plus they're overkill for our climate, which is also not that cold.

Anyone else dealing with this? I can see how it would be best to use the same glazing so as to not draw attention to any differences, but I think the 366 is overkill. Do you have triple pane windows and do they bother you?

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We have German triple paned windows and they don't bother us at all. It is getting dark out right now and I can see outside plus see reflections in the rooms where the lights are on. However, the only place where you see the triple reflection is where the light fixture is reflected, the rest of the reflection is not a triple reflection.

    Bookmark   August 13, 2013 at 8:20PM
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Thanks, dekeoboe-- maybe that is what she's trying to tell me. As to whether that is bothersome, it's pretty subjective! Sounds like it doesn't bother you, though, so good to hear first-hand. I assume you are in a cold climate? We heard that the Europeans were doing better at having solar gain plus good U-values, but didn't go that route. This has been the most pain and least fun of the house process so far! I'll be glad when it's done...

    Bookmark   August 13, 2013 at 8:36PM
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Windows on Washington Ltd

Where is the home located (climate region or specific).

There is a trade off between SHGC and total U-Factor.

The only way to maintain a high SHGC for passive solar and still get a lower (and possible qualified Energy Star 0.30 U-factor) is in triple pane in some cases.

The credit is so slight on windows now that I would focus on what is more proper vs what gets you the credit.

If high SHGC is better but gets you out of the E-Star range, go with your gut. The $200 will be saved via the more proper glass specifications and comfort.

Here is a link that might be useful: Cardinal Glass Stats

    Bookmark   August 13, 2013 at 11:18PM
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Hi Windows on WA (DC or State?) We are in the Puget Sound area-- not too hot, not too cold (just right!) For us, the 0.3 is a code requirement now, not a requirement for a rebate or credit or anything like that.

I've looked at pages and pages of specs on glazing and on windows (not the same numbers of course-- one gives you the relative difference among the types of glazing, but it is the second that gets plugged into the weighted average. We are required to meet the 0.3 U value overall. If it were just me, I'd skip the triple panes in our mild climate, knowing that we are doing many other energy saving things that don't "count" in the calculation. And we've been told the inspectors don't go around and check window by window to see that stickers match the schedule in the permit. Of course, all the risk would be on our end should this be the year they start doing that! We've come up with a compromise, using mostly 270, so we are sacrificing the solar gain potential to gain on the U-side since that is all the code cares about. I guess it's all evolving...

    Bookmark   August 14, 2013 at 8:00PM
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Windows on Washington Ltd

DC for us.

Talk to you code official. You might get a pass.

    Bookmark   August 14, 2013 at 8:32PM
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hi Lori,

If you take a look at the Cardinal website that WoW linked and look down at dual pane IGU's with LoE-180 on surface 2 and I89 on surface 4, in the 3/4" IGU (with argon fill)configuration you will see that combination results in a U.21 and SHGC .62.

These are glass only numbers so you will have to work with Milgard to see if that combination would work for you, but in your environment, and given your preferences, it could be a much better choice than triple or using a low solar heat gain coating.

If you have questions about surface 4 coatings, please take a peek at the thread "good replacement glass" for some comments on them.

Per European windows, they achieve higher SHGC because they use high solar gain coatings on low iron glass a lot more than is used in North America.

They get better U values in two ways, first because they use bulkier, better insulated, sash/frame combinations which some people like, but which some folks in North America feel are bulky.

Second, because Europeans calculate U value differently (not just using metric versus imperial), how they calculate performance will result in improved U value numbers over identical windows calculated using NFRC formula.

Which doesn't mean that Europeans don't make really good windows, because they do, but there is nothing inherently techno-superior that can't be done on this side of the pond if the window companies over here can be convinced that there is a market for them.

    Bookmark   August 14, 2013 at 9:51PM
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Epiarch Designs

I worked very closley with Kolbe on my tri-pane "tuning" of glass. I also worked with Inline (and some other fiberglass Canadian companies) who were great to work with and have great values, but we ultimately decided we wanted wood interiors instead of fiberglass. Now that the house is almost done, I sometimes wish we had all fiberglass! The wood is nice and warming though in our contemporary home. They are not trimmed out, but rather drywall returns.

We went with black exteriors and wood interiors. I selected Kolbe for those 2 options along with great product support and glass selection. Since the home is Energy Star 3.0, I had to hit the u .30 mark as well, and with aluminum clad that is about impossible right now with dual pane windows. The home is also highly efficient, so triple pane was always something I wanted to begin with. Sure, running the numbers, the payoff for dual vs triple for my heating zone 6 was quite high (20 some years) but the comfort is something that you can not put a value too.

I have a solar tuned home (not passive solar) and have about a SHGC value of .49 on my fixed south windows with a u of .17. Large casements are about .37 and .21. That was about the best combination I could get out of the triple panes. Now, my patio door is dual pane at .28 since the cost to up to triple was certainly not worth it in this case. (over 50% of the door cost). I have a dual pane door beside a triple pane window. I can see a VERY faint difference between the 2. Not greenish, but rather a very slightly more "hazy" out of the triples vs the dual. It is very faint, my wife does not really notice it....just "the window needs cleaned"....If I did not have a dual near it, I would not think anything of the triples.

Now back to the comfort. I have a west facing triple pane in the bedroom. Sun is lowering on a summer day, its roughly 98 degrees in the sun outside on the window. (open the window and take a temp reading). I close the window, take the air temp beside the glass and its about 78 degrees with the ac set point at 75. I do a similar test with the dual pane door and its about 85 degrees.

On the flip side, in the winter on my south windows with the SHG of .49, outside air temp is int he 20s, air temp near the glass is in the 60s. They also have not fogged up, even with minimal heat running and super high humidity levels such as when drywall was drying in January.

I did an addition on my parents home 2 years ago, right before I started mine. They used dual pane Eagle windows in their addition with some west facing glass. THe windows are about 30"x70", 2 of them. 5-7 pm in the summer those windows heat up the entire room about 5-10 degrees and since its a large space with poorly designed HVAC, it gets very uncomfortable. My home, prior to AC installed, never got above 77 degrees when it was in the upper 90s outside during the days.

Obviously its a tight, well insulated home (insulation does less for you in cooling vs heating anyway) but the glass and proper shading with overhangs contributes to a lot of that in cooling mode. We have no blinds in the home.

I would stop focusing so much on numbers at this point and consider other benefits you can gain by triple pane. You obviously know the numbers at this point, so I would recommend you focus on something else!

Best of luck

    Bookmark   August 15, 2013 at 2:49PM
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Thanks for your comments and all the details, Lzerarc (I’m a reader of your blog, which I found here some time ago��"I love following the projects of others as they don’t cause me any stress and don’t cost me any $$!)

“I would stop focusing so much on numbers at this point and consider other benefits you can gain by triple pane. You obviously know the numbers at this point, so I would recommend you focus on something else!”

I would like nothing more than to focus on what makes sense for us and our climate, but we are stuck with the numerical analysis and the 0.3 U-value as it is part of the 2009 Energy Code, which is applicable here. Knowing what I know about our location (which I’m intimately familiar with after having owned the property for many years), I would lean on the side of more heat gain in winter and sacrifice a little of the U-value. We don’t see anywhere near the temperatures you do��"no 10 degree days, and no 98 degree days. Forties are common in winter and a day above 80 is a big topic of “heat wave” conversation. More 50s and 60s than anything, which is why I was thinking that triple pane was overkill here. The house will have a fair amount of southern exposure, but the overhangs will shade the windows in summer. West windows don’t get much direct sun.

It is great to see your data, though, and I’m sure there are other readers in similar situations.

We’ve decided to take some time off yesterday and drive to Milgard and look at all the different types of glazing in person. We looked at the 180 vs 270 vs 366. I could see a difference when thy were side-by-side, but not of a magnitude that would bother me if they were on perpendicular planes in the same room. The 366 in triple glazing was noticeably darker, but I think it was more the triple pane than the coating type. I'm willing to live with it on a few of the north windows. We are making that tradeoff to get 180 on the southern exposure where we will appreciate the heat gain in winter. I'm so ready to be done with this decision and move on to the next batch!

Thanks oberon for your input as well. I understand the Europeans are ahead of us in some of the design issues. Knowing what I know now, I might have decided on a different type and manufacturer, but I just could not face the idea of starting over on the whole window plan. I think there is a lot of useful info here for the next person facing this question, and I appreciate the insights from everyone.

    Bookmark   August 17, 2013 at 3:46PM
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